WO2005054823A1 - Method and apparatus for determining the young's modulus of thin adhesive layers - Google Patents

Method and apparatus for determining the young's modulus of thin adhesive layers Download PDF

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Publication number
WO2005054823A1
WO2005054823A1 PCT/EP2004/053268 EP2004053268W WO2005054823A1 WO 2005054823 A1 WO2005054823 A1 WO 2005054823A1 EP 2004053268 W EP2004053268 W EP 2004053268W WO 2005054823 A1 WO2005054823 A1 WO 2005054823A1
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WO
WIPO (PCT)
Prior art keywords
adhesive
joining
modulus
joining elements
young
Prior art date
Application number
PCT/EP2004/053268
Other languages
French (fr)
Inventor
Jürgen Becher
Klaus Busl
Renate Yvonne Kreuzer
Georges Romanos
Gerhard Zill
Original Assignee
Henkel Loctite Deutschland Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE2003156865 external-priority patent/DE10356865A1/en
Application filed by Henkel Loctite Deutschland Gmbh filed Critical Henkel Loctite Deutschland Gmbh
Publication of WO2005054823A1 publication Critical patent/WO2005054823A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N19/00—Investigating materials by mechanical methods
    • G01N19/04—Measuring adhesive force between materials, e.g. of sealing tape, of coating
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0017—Tensile
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0075—Strain-stress relations or elastic constants
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0092—Visco-elasticity, solidification, curing, cross-linking degree, vulcanisation or strength properties of semi-solid materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
    • G01N2203/0262—Shape of the specimen
    • G01N2203/0278—Thin specimens
    • G01N2203/0282—Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
    • G01N2203/0298—Manufacturing or preparing specimens
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/04—Chucks, fixtures, jaws, holders or anvils
    • G01N2203/0423—Chucks, fixtures, jaws, holders or anvils using screws
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/04—Chucks, fixtures, jaws, holders or anvils
    • G01N2203/0429—Chucks, fixtures, jaws, holders or anvils using adhesive bond; Gluing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/44—Resins; Plastics; Rubber; Leather
    • G01N33/442—Resins; Plastics

Definitions

  • the invention relates to a method and an apparatus for determining the Young's modulus of thin adhesive layers.
  • the standards DIN5328, ASTM D 2095-96, DIN EN26922 and ASTM D 897-01 for the tensile strength of adhesive joints are concerned with the determination of the strength of the bond.
  • the adhesive joints have thicknesses of more than 0.2 millimetres, as is customary with epoxy adhesives. They are therefore not suitable for determining the Young's modulus of thinner layers.
  • the measuring methods operate using ultrasound, laser acoustics, in-situ SEM methods or dynamic-mechanical analyses and are in principle suitable for determining the Young's modulus of adhesive layers.
  • the test methods are however very expensive and the modulus values determined with physical test methods (e.g. ultrasound) differ from those determined using mechanical methods (tensile strength). Disclosure of Invention
  • the object of the invention is therefore to create a simple method and an apparatus suitable for it with which the Young's modulus of thin adhesive layers and sealant layers can be determined.
  • a precondition for this method is the production of adhesive joints and sealant layers with a defined layer thickness, and the object of the invention is therefore also a method and an apparatus for producing adhesive joints with a preset small layer thickness.
  • the invention is suitable in particular for measuring the Young's modulus of adhesive layers of anaerobic adhesives because these layers can be extremely thin and may even have no measurable thickness, the joining elements then physically touching in part-areas.
  • the connecting layers of silicone-based adhesives are also less than 0.2 mm thick.
  • Displacement sensors are preferably provided which are used both to set the gap between both parts of the testpiece and to record the extension, i.e. the change in gap width during the tensile test. These are preferably incremental displacement sensors. They operate in such a way that the divisions etched into a glass scale are read using an LED. The accuracy is approximately to within 0.2 micrometers. The zero point of the displacement sensors is ascertained by firstly pressing the two joining elements against each other without adhesive and choosing the reading obtained as the zero point.
  • Micrometers are preferably arranged on one of the joining elements, and the width of the gap between the joining elements is set to the approximate value by means of fitted micrometers before the application of the adhesive. The width of the gap is then adjusted after the application of the adhesive by means of the fitted micrometers, taking account of the distance values recorded by the displacement sensors.
  • testpiece After the adhesive has been applied and the gap width between the two joining elements set, the testpiece is preferably fixed by means of a fixing apparatus which clamps the two joining elements together until the adhesive has set.
  • FIG. 3 the right half of the arrangement of Figure 1 in vertical section with lines of force drawn in;
  • Fig. 4 the testpiece with the pusher casing, the fitted micrometers and the displacement sensors seen slanted from above;
  • Fig. 5 the arrangement of Fig. 4 seen slanted from below;
  • Fig. 6 the positioning device;
  • Fig. 7 the positioning device in the tensile testing machine and with the testpiece, the upper and the lower joining elements of the testpiece being separated;
  • Fig. 8 the fixing apparatus; and
  • Fig. 9 the force transducer in a side view.
  • the testpiece 10 is composed of a first, upper joining element 12 and a second, lower joining element 14 which are arranged in a pusher casing 16
  • the upper joining element 12 is a circular plate with a central opening 18 and a downward-pointing collar 20 surrounding the central opening.
  • the lower joining element 14 is likewise a circular plate with approximately the same external diameter as the upper joining element 12. It also has an upward-pointing circular rib 22 and a cavity 24 inside the rib 22.
  • the upper joining element 12 and the lower joining element 14 are axially symmetrical, and the collar 20 of the upper joining element 12 is aligned with the rib 22 of the lower joining element 14.
  • the facing end surfaces of the collar 20 and of the rib 22 represent the first and the second joining surfaces 26, 28, between which the adhesive is applied in a preset layer thickness, as will be explained below.
  • Both joining elements 12, 14 are held movable in axial direction in the pusher casing 16
  • the pusher casing 16 is a cylindrical sleeve 30 with a disk-shaped plate 31 on the top edge of the sleeve 30.
  • the disk-shaped plate 31 has a central opening, the upper joining element 12 resting on the top of the plate 31 and the central opening en- ' compassing the collar 20 of the upper joining element 12.
  • the cylindrical sleeve 30 surrounds the lower joining element 14 at a distance so that it does not rest against the inside of the pusher casing.
  • the disk-shaped plate 31 is positioned approximately centrally on the sleeve 30 and thus projects both outwards and inwards.
  • the thickness of that part of the disk-shaped plate 31 lying inside the sleeve 30 is approximately doubled directly on the sleeve wall and it narrows towards the central opening at an angle of approximately 37 degrees.
  • On the inner edge of the central opening the thickness of the plate is somewhat less than the height of the collar 20 of the upper joining element 12. In the tensile test, to be described below, this area of the pusher casing 16 transmits the force to the upper joining element 12 with the result that this increase in the plate thickness is useful for preventing as far as possible a deformation of the pusher casing 16
  • the upper joining element 12 is secured to the pusher casing 16 by means of screws 34. Moreover, there are mounted in the upper joining element 12, distributed around the periphery outside the collar 20, three fitted micrometers 36, the measuring pins of which lead inside the sleeve 30 through the plate 31 and press against the top of the lower joining element 14. Approximately in the middle between two fitted micrometers 36 and approximately on the same peripheral line as them is arranged in each case a displacement sensor 40 the measuring sensors 38 of which also lead inside the sleeve 30 through the plate 31 and record in axial direction the distance between the upper joining element 12 and the lower joining element 14 (Fig. 1).
  • the joining of the upper joining element 12 to the lower joining element 14 of the testpiece 10 is carried out by means of a positioning device 50 which is shown in Figure 6
  • the positioning device 50 has a base plate 52 and a top plate 54 both of which are shaped like an equilateral triangle with rounded corners.
  • Linear guides 56 are arranged in the corners.
  • Each of the linear guides 56 consists of a guide column 60 which is mounted in the base plate 52 and a guide sleeve 62 which is mounted in the top plate 54, and also of a ball bearing cage 64 which is arranged between the two.
  • a handwheel 66 Provided at the top end of one of the linear guides 55 is a handwheel 66, with which the top plate 54 can be moved visa-vis the base plate 52.
  • the linear guides 55 ensure that the top plate 54 is always aligned parallel to the base plate 52 during its upward or downward movement.
  • a circular, stepped opening 68 into which the pusher casing 16, together with the upper joining element 12 screwed fast to it, can be inserted.
  • the pusher casing 16 is secured in the opening 68 by means of cheese-head screws 70.
  • a cylindrical force transducer 72 Arranged on the base plate 52 in axial alignment thereto is a cylindrical force transducer 72 which carries the the lower joining element 14 of the testpiece 10 in axial alignment to the upper joining element 12 secured in the pusher casing 16 As shown in Figure 9, the force transducer 72 has a flat, circular projection 71 on its underside. This projection 71 fits with play into a corresponding recess 74 in the base plate 52.
  • a flat ball end 75 Provided on the top of the force transducer 72 is a flat ball end 75 on which the lower joining element 14 together with its indent 25 sits, again in axial alignment.
  • the lower joining element 14 is supported by the ball end 75 at only one point in the middle of the indent 25 and is therefore kept tillable by several degrees on the force transducer 72.
  • a pressure column 76 which ensures a preset mininxm distance between the base plate 52 and the top plate 54 and acts on the top plate 54 by means of a pressure spring 77 arranged in it before the top plate 54 is displaced downward to this mininxm distance.
  • the arrangement is affected such that the pressure springs 76 are somewhat compressed if the upper joining element 12 and the lower joining element 14 touch each other. The joining elements 12, 14 therefore lie on top of each other in the elastic area of the pressure springs 77.
  • the method for measuring the Young's modulus proceeds in two parts. In a first part, the upper joining element 12 and the lower joining element 14 of the testpiece 10 are joined together by means of the positioning device 50 with an adhesive of adjustable layer thickness. After the adhesive has set, the Young's modulus of this adhesive layer is then measured in a second part of the method.
  • Step 1 The lower joining element 14 of the testpiece 10 is positioned on the ball end 75 of the force transducer 72 which is secured axially and centrally on the base plate 52, and the upper joining element 12 is mounted in the top plate 54 by means of the pusher casing 16
  • Step 2 The top plate 54 is lowered by means of the handwheel 66 until it rests on the pressure springs 77 of the pressure columns 76 In this position the two joining elements 12 and 14 do not yet touch each other.
  • Step 3 The positioning device 50 is inserted into a tensile testing machine 80, a part of which is shown in Figure 7.
  • a tripod 82 engages at three points, distributed around the pusher casing 16, on the top plate 54. At its upper end it has an adapter 84 which is secured to the cross arm (not shown) of the tensile testing machine 80.
  • the top plate 54 is subjected via the tripod 82 to a preset force of 100 Newtons, this force being transmitted to the pusher casing 16 and the upper joining element 12 which is finally pressed with this force onto the lower joining element 14. Because it is housed tiltable on the ball end 75 of the force transducer 72 the lower joining element 14 necessarily aligns itself parallel to the upper joining element 12.
  • Step 4 In this position the fitted micrometers 36 and the displacement sensors 40 are set to zero, i.e. this position is defined as the zero point and the measuring scales are set accordingly.
  • Step 5 Relieving of the tensile testing machine 80 and separation of the upper joining element 12 from the lower joining element 14 by several millimeters by raising the top plate 54 by means of the handwheel 66 It is also possible to screw the tripod 82 to the cross arm of the tensile testing machine 80 and to the top plate 54 and to raise the top plate 54 by means of the tensile testing machine 80.
  • Step 6 Pre-setting the fitted micrometers 36 to the desired value of the layer thickness of the adhesive.
  • Step 7 Lowering of the top plate 54 until the fitted micrometers 36 rest on the lower joining element 14 and loading with the preset force of e.g. 100 Newtons.
  • Step 8 Monitoring the set layer thickness, i.e. the distance between the upper and the lower joining elements 12, 14 by means of the displacement sensors 40 and where necessary adjustment by means of the fitted micrometers 36
  • Step 9 Relieving of the tensile testing machine 80 and raising the top plate 54 and thereby separating the upper joining element 12 from the lower part 14.
  • Step 10 Removal of the lower joining element 14 from the force transducer 72, application of a sufficient quantity of adhesive to the joining surface 28 of the lower joining element 14 and replacing of the lower joining element 14 onto the force transducer 72.
  • an anti-twist device 58 it is ensured that the lower joining element 14, after the application of the adhesive, is replaced in the same rotation position vis-a-vis the upper joining element 12 from which it was previously removed, in order that the layer thickness set in step 8 is retained.
  • the anti-twist device 58 is a clamp which is secured to the lower edge of the sleeve 30 and engages in an indent 59 on the lower edge of the lower joining element 14.
  • Step 11 Lowering of the top plate 54 by means of the handwheel 66 or the tensile testing machine 80 until the fitted micrometers 36 touch the lower joining elements 14, and loading of the tensile testing machine 80.
  • the two joining elements 12, 14 are pressed against each other with the same force as was also applied in steps 3, 7 and 8, this force being chosen such that the adhesive or the sealant is distributed evenly over the joining surfaces 26, 28 in this present step 11.
  • Step 12 Fixing of the upper joining element 12 and the lower joining element 14 in this position by means of a fixing apparatus 86 which clamps the two joining elements 12, 14 against each other.
  • Step 13 Removal of the testpiece 10 together with the pusher casing 16, the testpiece 10 being fixed in its position by means of the fixing apparatus 86
  • the testpiece is removed from the positioning device 50 such that during the setting of the adhesive the positioning device 50 and the tensile testing machine 80 can be used elsewhere.
  • the adhesive can take several days to set completely.
  • the fixing device 86 (Fig. 8) is composed of a cylindrical spacer 88 which has an axial bore 90. Through the axial bore there passes a threaded rod 92, the lower end of which is screwed into a connection plate 94 whilst the end projecting from the other side of the spacer carries a helical pressure spring 96 which is clamped by means of a nut 98 against the top of the spacer.
  • the connection plate 94 is put through the opening 18 of the upper joining element 12 and screwed into the cavity 24, located inside the annular rib 22, of the lower joining element 14, then the spacer 88 is placed on the threaded rod 92, the spacer 88 resting on the top of the upper joining element 12.
  • the helical pressure spring 96 and a plain washer are pushed on, and the nut 98 is screwed onto the threaded rod and tightened, as a result of which the helical pressure spring 96 is clamped against the top of the spacer 88 and thereby the lower joining element 14 against the upper joining element 12.
  • the fixing apparatus 86 is installed whilst the testpiece 10 is still clamped in the tensile testing machine 80 by means of the tripod 82 so that the upper joining element 12, after the desired thickness of the adhesive layer has been set, is continuously clamped against the lower joining element 14.
  • the layer thickness can be continuously monitored by means of the displacement sensors 40.
  • the Young's modulus is then measured in the second part of the method.
  • the fixing apparatus 86 is removed and the testpiece 10, together with the pusher casing 16, in which the fitted micrometers 36 and the displacement sensors 40 are mounted, is inserted into the tensile testing machine 80, after placing a solid plate underneath.
  • the positioning device 50 is not used here.
  • a force transducer Secured to the cross bar, not shown, of the tensile testing machine 80, is a force transducer, also not shown, to which a pusher 100 is in turn attached.
  • the pusher 100 By lowering the cross bar, the pusher 100 is moved through the opening 18 of the upper joining element 12 into the cavity 24 in the annular rib 22 of the lower joining element 14, a small compression piece having previously been inserted into the cavity 24 to protect the lower joining element 14 against damage.
  • the head of the pusher 100 is rounded to ensure that only a uniaxial force component is exerted on the lower joining element 14. Then the pusher 100 is acted on by means of the tensile testing machine 80, the force recorded by the force transducer and the displacement, detected by the displacement sensors 40, of the lower joining element 14 vis-a-vis the upper joining element 12 being recorded in relation to one another.
  • the pusher casing 16 now serves to expel the lower joining element 14, and the cylindrical sleeve 30 therefore extends up under the bottom of the lower joining element 14 (Fig. 5).
  • the cross bar in the tensile testing machine 80 is lowered at a speed of 0.5 millimetres per minute.
  • the plotted readings of the force transducer attached to the cross bar and of the displacement sensors 40 produce a stress-strain diagram.
  • the initial pitch of the plotted curves gives the Young's modulus of the adhesive at the set layer thickness, the curve plotted by the displacement sensors 40 to largely agree. If the plotted curves differ by more than 5% the test is rejected.
  • the Young's modulus of the adhesive is determined by drawing a straight line to the initial part of the stress-strain curve.
  • the strain increment which corresponds to a stress increment, is taken from this line and inserted into equation 3.
  • the Poisson's ratio v can be calculated with the results of the shear modulus determination. [058] If a Poisson's ratio between 0.3 and 0.45 is assumed, the multiplication factor can vary between 0.74 and 0.26 Due to the hindered transverse contraction it is clear that the measured value is approximately three times the value of the Young's modulus of a solids testpiece.
  • testpiece 10 testpiece 12 upper joining element 14 lower joining element 16 pusher casing 18 opening 20 collar 22 ribs 24 cavity 25 indent first joining surface second joining surface sleeve plate fillet screws fitted micrometers measuring sensors displacement sensors positioning device base plate top plate linear guides anti-twist device indent guide column guide sleeve ball bearing cage hand wheel opening cheese-head screws projection force transducer recess ball end pressure column pressure spring tensile testing machine tripod adapter fixing appratus spacer bore threaded rod connection plate 96 helical pressure spring 98 nut 100 pusher

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Abstract

To determine the Young's modulus of adhesive layers or sealant layers less than 1 mm, preferably less than 0.2 mm thick, the following steps are carried out: application of the adhesive to at least one of two joining elements; arranging the two joining elements with a joining gap of a preset width of less than 1 mm; allowing the adhesive to set; exerting of a force on both joining elements in the direction of a separation of the two joining elements; plotting the change in the gap width as a function of the size of the force acting on the joining elements. The Young's modulus of the adhesive is calculated according to the formula: Eadhesive = ( σz / ϵz ) ·[( 1 + ν ) · ( 1 - 2ν ) / ( 1 - ν )], where σz / ϵz = Ehindered is the Young's modulus measured according to the invention. To produce an adhesive layer or sealant layer of a defined layer thickness in the joining gap the following steps are carried out: pressing the two joining elements against each other before the application of the adhesive and setting the displacement sensors to zero; and setting the gap width before the application of the adhesive or sealant in accordance with the values displayed by the displacement sensors. The gap width is set by means of fitted micrometers, the width of the gap between the joining elements being set to the approximate value by means of the fitted micrometers before the application of the adhesive, and the width of the gap after the application of the adhesive being adjusted by means of the fitted micrometers and taking account of the display of the displacement sensors.

Description

Description Method and apparatus for determining the Young's modulus of thin adhesive layers Technical Field [001] The invention relates to a method and an apparatus for determining the Young's modulus of thin adhesive layers.
[002] Modern design methods contain mathematical model calculations (finite element method [FEM]). Numerical methods reduce the number of required tests, shorten the development time and make design changes easier. While the mechanical behaviour of metals is well known and incorporated in most FE software packages, application- specific tests must be carried out for non-linear materials such as adhesives and liquid seals in order to obtain the required values. These are Young's modulus and the shear modulus which are linked by Poisson's ratio. Background Art
[003] Methods for measuring the shear modulus are known. As the direct measurement of the Poisson's ratio is extremely difficult in the case of thin layers, it is advisable to determine the Young's modulus. This is usually determined using dog-bone-like solid bodies. The measurement values obtained with such bodies however are informative only for thick adhesive layers. The properties of thin adhesive layers and sealant layers between two substrates can differ markedly from these.
[004] The standards DIN5328, ASTM D 2095-96, DIN EN26922 and ASTM D 897-01 for the tensile strength of adhesive joints are concerned with the determination of the strength of the bond. The adhesive joints have thicknesses of more than 0.2 millimetres, as is customary with epoxy adhesives. They are therefore not suitable for determining the Young's modulus of thinner layers.
[005] Various methods for determining the Young's modulus are known from the literature:
[006] Sonne, H.M. "Bestimtmng des Elastizitatsmoduls im Zugversuch" [Determination of Young's Modulus in Tensile Tests] Werkstoffprufung 1999, p. 219-230
[007] Schneider, D., Schultrich, B. "Mechanische Charakterisierung von harten and su- perharten Schichten durch Messung des E-Moduls mit Laserakustik" [Mechanical Characterization of Hard and Super-hard Layers by Measuring the Young's Modulus with Laser Acoustics] Werkstoffprufung 1998, p. 183-193
[008] Hohberg, R. "E-modul-Prufinethodik" [Young's Modulus Testing Methods] MP Materialprufung, Vol. 43 (2001) 10 [009] Aegerter, J., Blocbing, H., Sonne, H.M. "Influence of the Testing Speed on the Yield/Proof Strength" MP Materialprufung, Vol. 43 (2001) 10
[010] Ledworuski, S, Ell, M., Kϋhn, H.-J. "Den Elastizitatsmodul sicher bestirrmen" [Reliably Determining the Young's Modulus] MP Materialprufung, Vol. 42 (2000) 4
[011] Buc , A. "Relations between the Elastic Moduli of Pure Metals" MP Materialprufung, Vol. 43 (2001) 11-12
[012] Wetzig, K. "In situ REM-Methoden in der Werkstoffforschung nutzen" [Using In- Situ SEM Methods in Material Research] MP Materialprufung, Vol. 39 (1997) 5
[013] The measuring methods operate using ultrasound, laser acoustics, in-situ SEM methods or dynamic-mechanical analyses and are in principle suitable for determining the Young's modulus of adhesive layers. The test methods are however very expensive and the modulus values determined with physical test methods (e.g. ultrasound) differ from those determined using mechanical methods (tensile strength). Disclosure of Invention
[014] The object of the invention is therefore to create a simple method and an apparatus suitable for it with which the Young's modulus of thin adhesive layers and sealant layers can be determined.
[015] A precondition for this method is the production of adhesive joints and sealant layers with a defined layer thickness, and the object of the invention is therefore also a method and an apparatus for producing adhesive joints with a preset small layer thickness.
[016] This object is achieved according to the invention by a method according to claims 1 and 4 and an apparatus according to claim 6
[017] The invention is suitable in particular for measuring the Young's modulus of adhesive layers of anaerobic adhesives because these layers can be extremely thin and may even have no measurable thickness, the joining elements then physically touching in part-areas. The connecting layers of silicone-based adhesives are also less than 0.2 mm thick.
[018] Displacement sensors are preferably provided which are used both to set the gap between both parts of the testpiece and to record the extension, i.e. the change in gap width during the tensile test. These are preferably incremental displacement sensors. They operate in such a way that the divisions etched into a glass scale are read using an LED. The accuracy is approximately to within 0.2 micrometers. The zero point of the displacement sensors is ascertained by firstly pressing the two joining elements against each other without adhesive and choosing the reading obtained as the zero point.
[019] Micrometers are preferably arranged on one of the joining elements, and the width of the gap between the joining elements is set to the approximate value by means of fitted micrometers before the application of the adhesive. The width of the gap is then adjusted after the application of the adhesive by means of the fitted micrometers, taking account of the distance values recorded by the displacement sensors.
[020] After the adhesive has been applied and the gap width between the two joining elements set, the testpiece is preferably fixed by means of a fixing apparatus which clamps the two joining elements together until the adhesive has set.
[021] The transverse strain ratio required for finite element calculation can be ascertained from the results of the shear and tensile tests. It mist be borne in mind that in the method according to the invention the procedure of the tensile test is that a triaxial stressed state forms with a simultaneous uniaxial deformed state, i.e. the transverse strain of the adhesive layer subjected to normal stress is hindered (ε = ε = 0). x y According to the generalized Hooke's law, the following is under these conditions obtained for the Young's modulus of the adhesive [022] E adhesive = ( σ z/ ε z) - [( l + v ) . ( l - 2v ) / ( l - v )],
[023] where σ / ε = E is the hindered Young's modulus measured with the help of z z hindered the method according to the invention. [024] The Poisson's ratio v can be calculated, with the help of the existing relationship between Young's modulus and shear modulus G = E / [2 ( 1 + v )], with the results of the shear modulus determination. Brief Description of the Drawings [025] An embodiment of the invention will be explained below using the drawing. There are shown in: Fig. 1 the two-part testpiece and the pusher casing, in vertical section; Fig. 2 the two-part testpiece and the pusher casing, in a three- dimensional section view; Fig. 3 the right half of the arrangement of Figure 1 in vertical section with lines of force drawn in; Fig. 4 the testpiece with the pusher casing, the fitted micrometers and the displacement sensors seen slanted from above; Fig. 5 the arrangement of Fig. 4 seen slanted from below; Fig. 6 the positioning device; Fig. 7 the positioning device in the tensile testing machine and with the testpiece, the upper and the lower joining elements of the testpiece being separated; Fig. 8 the fixing apparatus; and Fig. 9 the force transducer in a side view. Mode for the Invention [026] As shown in Figures 1 and 2, the testpiece 10 is composed of a first, upper joining element 12 and a second, lower joining element 14 which are arranged in a pusher casing 16 The upper joining element 12 is a circular plate with a central opening 18 and a downward-pointing collar 20 surrounding the central opening. The lower joining element 14 is likewise a circular plate with approximately the same external diameter as the upper joining element 12. It also has an upward-pointing circular rib 22 and a cavity 24 inside the rib 22. The upper joining element 12 and the lower joining element 14 are axially symmetrical, and the collar 20 of the upper joining element 12 is aligned with the rib 22 of the lower joining element 14. The facing end surfaces of the collar 20 and of the rib 22 represent the first and the second joining surfaces 26, 28, between which the adhesive is applied in a preset layer thickness, as will be explained below. Both joining elements 12, 14 are held movable in axial direction in the pusher casing 16 The pusher casing 16 is a cylindrical sleeve 30 with a disk-shaped plate 31 on the top edge of the sleeve 30. The disk-shaped plate 31 has a central opening, the upper joining element 12 resting on the top of the plate 31 and the central opening en- ' compassing the collar 20 of the upper joining element 12. The cylindrical sleeve 30 surrounds the lower joining element 14 at a distance so that it does not rest against the inside of the pusher casing. The disk-shaped plate 31 is positioned approximately centrally on the sleeve 30 and thus projects both outwards and inwards. The thickness of that part of the disk-shaped plate 31 lying inside the sleeve 30 is approximately doubled directly on the sleeve wall and it narrows towards the central opening at an angle of approximately 37 degrees. On the inner edge of the central opening the thickness of the plate is somewhat less than the height of the collar 20 of the upper joining element 12. In the tensile test, to be described below, this area of the pusher casing 16 transmits the force to the upper joining element 12 with the result that this increase in the plate thickness is useful for preventing as far as possible a deformation of the pusher casing 16
[027] In Figure 3 the lines of force are drawn in and it can be seen that the lines run essentially parallel to the joining surfaces 26, 28 and that the pressure inside the joining surfaces 26, 28 is essentially uniform. In order to achieve this uniformity, the point at which the collar 20 is placed on the plate of the upper joining element 12 is provided with a fillet 32 with a semicircular profile which extends into the plate of the upper joining element 12. As can also be seen in Figures 1 and 2, the joining surface 28 of the lower joining element 14 is somewhat wider than the first joining surface 26 of the upper joining element 12.
[028] As can be seen in Figures 4 and 5, the upper joining element 12 is secured to the pusher casing 16 by means of screws 34. Moreover, there are mounted in the upper joining element 12, distributed around the periphery outside the collar 20, three fitted micrometers 36, the measuring pins of which lead inside the sleeve 30 through the plate 31 and press against the top of the lower joining element 14. Approximately in the middle between two fitted micrometers 36 and approximately on the same peripheral line as them is arranged in each case a displacement sensor 40 the measuring sensors 38 of which also lead inside the sleeve 30 through the plate 31 and record in axial direction the distance between the upper joining element 12 and the lower joining element 14 (Fig. 1).
[029] The joining of the upper joining element 12 to the lower joining element 14 of the testpiece 10 is carried out by means of a positioning device 50 which is shown in Figure 6 The positioning device 50 has a base plate 52 and a top plate 54 both of which are shaped like an equilateral triangle with rounded corners. Linear guides 56, each aligned normal relative to the plate surfaces, are arranged in the corners. Each of the linear guides 56 consists of a guide column 60 which is mounted in the base plate 52 and a guide sleeve 62 which is mounted in the top plate 54, and also of a ball bearing cage 64 which is arranged between the two. Provided at the top end of one of the linear guides 55 is a handwheel 66, with which the top plate 54 can be moved visa-vis the base plate 52. The linear guides 55 ensure that the top plate 54 is always aligned parallel to the base plate 52 during its upward or downward movement.
[030] Provided in the middle of the top plate 54 is a circular, stepped opening 68 into which the pusher casing 16, together with the upper joining element 12 screwed fast to it, can be inserted. As shown in Figure 7, the pusher casing 16 is secured in the opening 68 by means of cheese-head screws 70.
[031] Arranged on the base plate 52 in axial alignment thereto is a cylindrical force transducer 72 which carries the the lower joining element 14 of the testpiece 10 in axial alignment to the upper joining element 12 secured in the pusher casing 16 As shown in Figure 9, the force transducer 72 has a flat, circular projection 71 on its underside. This projection 71 fits with play into a corresponding recess 74 in the base plate 52. Provided on the top of the force transducer 72 is a flat ball end 75 on which the lower joining element 14 together with its indent 25 sits, again in axial alignment. The lower joining element 14 is supported by the ball end 75 at only one point in the middle of the indent 25 and is therefore kept tillable by several degrees on the force transducer 72.
[032] Also arranged on each of the linear guides 55 is a pressure column 76 which ensures a preset mininxm distance between the base plate 52 and the top plate 54 and acts on the top plate 54 by means of a pressure spring 77 arranged in it before the top plate 54 is displaced downward to this mininxm distance. In the process, the arrangement is affected such that the pressure springs 76 are somewhat compressed if the upper joining element 12 and the lower joining element 14 touch each other. The joining elements 12, 14 therefore lie on top of each other in the elastic area of the pressure springs 77.
[033] The method for measuring the Young's modulus proceeds in two parts. In a first part, the upper joining element 12 and the lower joining element 14 of the testpiece 10 are joined together by means of the positioning device 50 with an adhesive of adjustable layer thickness. After the adhesive has set, the Young's modulus of this adhesive layer is then measured in a second part of the method.
[034] The first part of the method proceeds as follows:
[035] Step 1 : The lower joining element 14 of the testpiece 10 is positioned on the ball end 75 of the force transducer 72 which is secured axially and centrally on the base plate 52, and the upper joining element 12 is mounted in the top plate 54 by means of the pusher casing 16
[036] Step 2: The top plate 54 is lowered by means of the handwheel 66 until it rests on the pressure springs 77 of the pressure columns 76 In this position the two joining elements 12 and 14 do not yet touch each other.
[037] Step 3: The positioning device 50 is inserted into a tensile testing machine 80, a part of which is shown in Figure 7. A tripod 82 engages at three points, distributed around the pusher casing 16, on the top plate 54. At its upper end it has an adapter 84 which is secured to the cross arm (not shown) of the tensile testing machine 80. The top plate 54 is subjected via the tripod 82 to a preset force of 100 Newtons, this force being transmitted to the pusher casing 16 and the upper joining element 12 which is finally pressed with this force onto the lower joining element 14. Because it is housed tiltable on the ball end 75 of the force transducer 72 the lower joining element 14 necessarily aligns itself parallel to the upper joining element 12. There is still no adhesive between the upper joining element 12 and the lower joining element 14. [038] Step 4: In this position the fitted micrometers 36 and the displacement sensors 40 are set to zero, i.e. this position is defined as the zero point and the measuring scales are set accordingly. [039] Step 5: Relieving of the tensile testing machine 80 and separation of the upper joining element 12 from the lower joining element 14 by several millimeters by raising the top plate 54 by means of the handwheel 66 It is also possible to screw the tripod 82 to the cross arm of the tensile testing machine 80 and to the top plate 54 and to raise the top plate 54 by means of the tensile testing machine 80. [040] Step 6: Pre-setting the fitted micrometers 36 to the desired value of the layer thickness of the adhesive. [041] Step 7: Lowering of the top plate 54 until the fitted micrometers 36 rest on the lower joining element 14 and loading with the preset force of e.g. 100 Newtons. [042] Step 8: Monitoring the set layer thickness, i.e. the distance between the upper and the lower joining elements 12, 14 by means of the displacement sensors 40 and where necessary adjustment by means of the fitted micrometers 36
[043] Step 9: Relieving of the tensile testing machine 80 and raising the top plate 54 and thereby separating the upper joining element 12 from the lower part 14.
[044] Step 10: Removal of the lower joining element 14 from the force transducer 72, application of a sufficient quantity of adhesive to the joining surface 28 of the lower joining element 14 and replacing of the lower joining element 14 onto the force transducer 72. By using an anti-twist device 58 it is ensured that the lower joining element 14, after the application of the adhesive, is replaced in the same rotation position vis-a-vis the upper joining element 12 from which it was previously removed, in order that the layer thickness set in step 8 is retained. The anti-twist device 58 is a clamp which is secured to the lower edge of the sleeve 30 and engages in an indent 59 on the lower edge of the lower joining element 14.
[045] Step 11 : Lowering of the top plate 54 by means of the handwheel 66 or the tensile testing machine 80 until the fitted micrometers 36 touch the lower joining elements 14, and loading of the tensile testing machine 80. The two joining elements 12, 14 are pressed against each other with the same force as was also applied in steps 3, 7 and 8, this force being chosen such that the adhesive or the sealant is distributed evenly over the joining surfaces 26, 28 in this present step 11. [046] Step 12: Fixing of the upper joining element 12 and the lower joining element 14 in this position by means of a fixing apparatus 86 which clamps the two joining elements 12, 14 against each other.
[047] Step 13: Removal of the testpiece 10 together with the pusher casing 16, the testpiece 10 being fixed in its position by means of the fixing apparatus 86
[048] In the last step, the testpiece is removed from the positioning device 50 such that during the setting of the adhesive the positioning device 50 and the tensile testing machine 80 can be used elsewhere. The adhesive can take several days to set completely.
[049] The fixing device 86 (Fig. 8) is composed of a cylindrical spacer 88 which has an axial bore 90. Through the axial bore there passes a threaded rod 92, the lower end of which is screwed into a connection plate 94 whilst the end projecting from the other side of the spacer carries a helical pressure spring 96 which is clamped by means of a nut 98 against the top of the spacer. The connection plate 94 is put through the opening 18 of the upper joining element 12 and screwed into the cavity 24, located inside the annular rib 22, of the lower joining element 14, then the spacer 88 is placed on the threaded rod 92, the spacer 88 resting on the top of the upper joining element 12. Then the helical pressure spring 96 and a plain washer are pushed on, and the nut 98 is screwed onto the threaded rod and tightened, as a result of which the helical pressure spring 96 is clamped against the top of the spacer 88 and thereby the lower joining element 14 against the upper joining element 12. The fixing apparatus 86 is installed whilst the testpiece 10 is still clamped in the tensile testing machine 80 by means of the tripod 82 so that the upper joining element 12, after the desired thickness of the adhesive layer has been set, is continuously clamped against the lower joining element 14. The layer thickness can be continuously monitored by means of the displacement sensors 40.
[050] After the adhesive has set, the Young's modulus is then measured in the second part of the method. For this purpose, the fixing apparatus 86 is removed and the testpiece 10, together with the pusher casing 16, in which the fitted micrometers 36 and the displacement sensors 40 are mounted, is inserted into the tensile testing machine 80, after placing a solid plate underneath. The positioning device 50 is not used here. Secured to the cross bar, not shown, of the tensile testing machine 80, is a force transducer, also not shown, to which a pusher 100 is in turn attached. By lowering the cross bar, the pusher 100 is moved through the opening 18 of the upper joining element 12 into the cavity 24 in the annular rib 22 of the lower joining element 14, a small compression piece having previously been inserted into the cavity 24 to protect the lower joining element 14 against damage. The head of the pusher 100 is rounded to ensure that only a uniaxial force component is exerted on the lower joining element 14. Then the pusher 100 is acted on by means of the tensile testing machine 80, the force recorded by the force transducer and the displacement, detected by the displacement sensors 40, of the lower joining element 14 vis-a-vis the upper joining element 12 being recorded in relation to one another. The pusher casing 16 now serves to expel the lower joining element 14, and the cylindrical sleeve 30 therefore extends up under the bottom of the lower joining element 14 (Fig. 5). The cross bar in the tensile testing machine 80 is lowered at a speed of 0.5 millimetres per minute. [051] The plotted readings of the force transducer attached to the cross bar and of the displacement sensors 40 produce a stress-strain diagram. The initial pitch of the plotted curves gives the Young's modulus of the adhesive at the set layer thickness, the curve plotted by the displacement sensors 40 to largely agree. If the plotted curves differ by more than 5% the test is rejected. In the case of an axially loaded testpiece, the stress is defined by the following forrmla: σ = F / A (l) where σ is the tensile stress [MPa] F is the force applied [N] 2 A is the joining surface [mm ]. The tensile strain in the adhesive is: ε = Δl / l (2) o where ε is the tensile strain Δl is the deformation 1 is the thickness of the adhesive layer (run), o The Young's modulus is defined as the inclination of the linear initial part of the stress- strain curve. E = Δσ / Δε (3)
[052] The Young's modulus of the adhesive is determined by drawing a straight line to the initial part of the stress-strain curve. The strain increment, which corresponds to a stress increment, is taken from this line and inserted into equation 3.
[053] The Poisson' s ratio required for the finite element calculation can be ascertained from the results of the shear and tensile tests. It is to be borne in mind that in the tensile test carried out within the framework of the invention a triaxial stressed state is produced with a simultaneous uniaxial deformation state, i.e. the transverse strain of the adhesive layer subjected to normal stress is prevented. The generalized Hooke's law for isotropic substances states: ε =(l/E)-[σ -v(σ +σ)];(4) εX = (l/E)-[σX- (σχ y+σz)];(5) y=(l/E)-[σy- (σX+σZ)];(6) z z x y
[054] The fact that no transverse contraction takes place means: εχ = 0;(7) εX = 0;(8) y [055] Inserted into equations 4 and 5, this gives: σ = v (σ + σ ); (9) σ = v (σ + σ ); (10) σ = σ = [v /(l - v)] • σ ; (11) y x z x y z
[056] With this expression, equation (6) can be written as: ε =(σ/E).(l + v)-(l~2v)/(l-v);(12) z z or solved according to Young's modulus: E = ( σ / ε ) • ( 1 + v ) • ( 1 - 2 ) / ( 1 - v) ; (13) z z where ( σ / ε ) is the hindered Young's modulus measured with the help of this z z method. With the help of the existing relationship between Young's modulus and shear modulus G = E[2(l+v)](14) [057] the Poisson's ratio v can be calculated with the results of the shear modulus determination. [058] If a Poisson's ratio between 0.3 and 0.45 is assumed, the multiplication factor can vary between 0.74 and 0.26 Due to the hindered transverse contraction it is clear that the measured value is approximately three times the value of the Young's modulus of a solids testpiece. [059] List of reference numbers 10 testpiece 12 upper joining element 14 lower joining element 16 pusher casing 18 opening 20 collar 22 ribs 24 cavity 25 indent first joining surface second joining surface sleeve plate fillet screws fitted micrometers measuring sensors displacement sensors positioning device base plate top plate linear guides anti-twist device indent guide column guide sleeve ball bearing cage hand wheel opening cheese-head screws projection force transducer recess ball end pressure column pressure spring tensile testing machine tripod adapter fixing appratus spacer bore threaded rod connection plate 96 helical pressure spring 98 nut 100 pusher

Claims

Claims
[001] A method for determining the Young's modulus of adhesive layers or sealant layers less than 1 m, preferably less than 0.2 mm thick, the method comprising the following steps: preparation of a testpiece composed of two joining elements, the two joining elements (12, 14) having facing, parallel joining surfaces (26, 28); application of the adhesive to at least one of the joining surfaces (26, 28) arranging the two joining elements (12, 14) such that the joining surfaces (26, 28) form a gap of a preset width of less than 1 mm, preferably less than 0.2 mm, which is filled with the adhesive; allowing the adhesive to set; exertion of a force on the two joining elements (12, 14) which is directed normally relative to the joining surfaces (26, 28) and acts in the direction of a separation of the two joining elements (12, 14); plotting the change in the gap width as a function of the size of the force acting on the joining elements (12, 14). [002] The method according to claim 1, including the step: determining the Young's modulus of the adhesive according to the formula E = ( σ / ε ) -[( l + v ) - ( l - 2v ) / ( l - v )], adhesive z z where σ / ε = E is the Young's modulus measured with the method z z hindered according to claim 1.
[003] The method according to claim 2, including the step: calculating the Poisson's ratio v from the relationship between Young's modulus and shear modulus, which is reproduced by the equation G = E / [ 2 - ( l + v )].
[004] A method for the production of an adhesive layer or sealant layer of a defined layer thickness in a gap which is delimited by joining surfaces (26, 28) of two joining elements (12, 14), in particular for carrying out the method according to one of claims 1 to 3, comprising the following steps: recording the change in the gap width by means of displacement sensors (40) as a function of the size of the force acting on the joining elements (12, 14), and setting the displacement sensors (40) to zero; pressing the two joining elements (12, 14) against each other before the application of the adhesive, the obtained display of the displacement sensors (40) being chosen as the zero point; and setting the gap width before the application of the adhesive or sealant in accordance with the values displayed by the displacement sensors (40).
[005] The method according to claim 4, wherein the gap width being set by means of fitted micrometers (36); the width of the gap between the joining elements (12, 14) being set to the approximate value by means of the fitted micrometers (36) before the application of the adhesive; and the width of the gap being adjusted by means of the fitted micrometers (36) after the application of the adhesive and taking account of the display of the displacement sensors (40).
[006] An apparatus for use with the method according to one of claims 1 to 5, with a testpiece (10) which has an upper joining element (12), and a lower joining element (14), and with a pusher casing (16) on one end of which the upper joining element (12) rests and the lower joining element (14) being able to be inserted with play at the other end of the pusher casing (16).
[007] The apparatus according to claim 6, displacement sensors (40) being mounted on the first joining element (12), by means of which a change in the distance between the joining surfaces (26, 28) of the two joining elements (12, 14) can be recorded.
[008] The apparatus according to claim 7, characterized in that fitted micrometers (36) are attached to the first joining element (12), by means of which the distance between the joining surfaces (26, 28) can be set.
[009] The apparatus according to one of claims 6 to 8, with a fixing apparatus (86) which clamps the two joining elements (12, 14) against each other.
PCT/EP2004/053268 2003-12-03 2004-12-03 Method and apparatus for determining the young's modulus of thin adhesive layers WO2005054823A1 (en)

Applications Claiming Priority (4)

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DE10356865.4 2003-12-03
DE2003156865 DE10356865A1 (en) 2003-12-03 2003-12-03 Method for determining Young's modulus of anaerobic adhesive layer, involves exerting force on joining elements of testpiece, along direction which is perpendicular to surfaces of joining elements
US53092303P 2003-12-22 2003-12-22
US60/530,923 2003-12-22

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CN102980507A (en) * 2012-12-17 2013-03-20 吉林大学 Measuring method for length of metal wire to be measured in young modulus measurement instrument
CN104299483A (en) * 2014-09-29 2015-01-21 安徽农业大学 Bridge type Young modulus combined instrument

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CN102980507A (en) * 2012-12-17 2013-03-20 吉林大学 Measuring method for length of metal wire to be measured in young modulus measurement instrument
CN102980507B (en) * 2012-12-17 2015-12-23 吉林大学 The measuring method of wire length to be measured in modulus measurer
CN104299483A (en) * 2014-09-29 2015-01-21 安徽农业大学 Bridge type Young modulus combined instrument

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