CN108548719B - Method for testing interlayer normal strength of composite material - Google Patents
Method for testing interlayer normal strength of composite material Download PDFInfo
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- CN108548719B CN108548719B CN201810186065.8A CN201810186065A CN108548719B CN 108548719 B CN108548719 B CN 108548719B CN 201810186065 A CN201810186065 A CN 201810186065A CN 108548719 B CN108548719 B CN 108548719B
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- 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
Abstract
The invention discloses a method for testing the interlayer normal strength of a composite material, and belongs to the technical field of composite material and material performance testing. According to the method, a test piece is a square flat plate block, a polytetrafluoroethylene film which does not cover a test area is inserted between an upper layer and a lower layer of a preset test interface in the paving process, and then the polytetrafluoroethylene film is cured and molded; and testing the interlayer strength of the composite material by using a testing device. The invention relates to a method for testing the normal tensile strength between layers of a composite material, which breaks through the limitation of the previous method on the interlayer performance of a test piece to be tested. The size of the corresponding polytetrafluoroethylene film hollow area can be designed according to the interlayer performance of the composite material to be tested, so that the normal damage load between layers in the test is controlled, the interlayer damage of the composite material is guaranteed to be prior to the adhesive damage between the metal block and the test piece, and the damage mode is further guaranteed.
Description
Technical Field
The invention belongs to the technical field of composite materials and material performance testing, and relates to a method for testing the interlayer normal strength of a composite material and a method for designing and manufacturing a test piece of the composite material.
Background
The composite material has the characteristics of light weight, high strength and the like, and is widely applied to the fields of sports, aviation, aerospace and the like. The advanced composite material is specially used for a main bearing structure or a secondary bearing structure, has rigidity and strength performance equivalent to or superior to those of aluminum alloy, and mainly refers to a reinforced composite material with high strength and modulus, such as boron fiber, carbon fiber, aramid fiber and the like at present. Although the performance of the composite material is equivalent to or stronger than that of metal, the interlaminar performance of the composite material is very low, and the interlaminar bearing only by the interlaminar interface is an area which is easy to damage, so that the interlaminar strength of the composite material must be measured for evaluating the quality and the performance of the composite material.
At present, no method for testing the interlayer normal strength of the carbon fiber composite material exists, although GB/T4944 can measure the interlayer tensile strength of the glass fiber laminate, the bonding strength of a test piece and a metal binder is required to be higher than the interlayer tensile strength of the test piece, and the interlayer performance of the advanced composite material is often higher than the bonding strength of the binder, so that the failure mode of the test piece is contrary to the expectation, and the measured performance is inaccurate.
Disclosure of Invention
The invention aims to provide a testing method capable of accurately testing the interlayer normal strength of all advanced composite materials. The invention provides a method for testing the interlayer normal strength of a composite material, which comprises the following two steps:
in the first step, films and test pieces were prepared.
The test piece is a square flat plate block, a polytetrafluoroethylene film which does not cover a test area is inserted between an upper layer and a lower layer of a preset test interface in the paving process (the polytetrafluoroethylene film can be properly adjusted in size according to requirements, and if the interlayer performance of the composite material to be tested is high, the test area can be properly reduced), and then the polytetrafluoroethylene film is cured and molded.
And secondly, testing the interlayer strength of the composite material by using a testing device.
The test device comprises two metal blocks with through holes and two load transmission joints, wherein the end faces of the metal blocks are respectively bonded with the upper layer and the lower layer of the test piece, one ends of the two load transmission joints are respectively connected with the testing machine, and the other ends of the two load transmission joints are respectively connected with the two metal blocks through the through holes in the metal blocks.
And applying unidirectional tensile load to the load-transmitting joints at the two sides until the test piece is subjected to interlaminar failure, and recording the failure load P (the unit is N). Calculating the interlaminar normal tensile strength sigma of the composite materialn：
Wherein, the inner and outer diameters R of the upper ring of the film1、R2And the width w of the spokes on the film is in mm, sigmanIn Mpa.
The test piece and the film have the same shape and size.
The invention has the advantages that:
(1) the invention relates to a method for testing the normal tensile strength between layers of a composite material, which breaks through the limitation of the previous method on the interlayer performance of a test piece to be tested.
(2) According to the method for testing the interlayer normal tensile strength of the composite material, the polytetrafluoroethylene film is inserted into the test interlayer to manufacture the test piece, the metal blocks are adhered to the upper surface and the lower surface of the test piece, and the load transmission joint is used for loading, so that the test piece is subjected to interlayer normal tensile damage, and the interlayer normal tensile strength is measured.
(3) The test piece designed in the invention has originality and has the advantages that the size of the corresponding polytetrafluoroethylene film hollowed-out area can be designed according to the interlayer performance of the composite material to be tested, so that the normal damage load between layers in the test is controlled, the interlayer damage of the composite material is guaranteed to be prior to the adhesive damage between the metal block and the test piece, and the damage mode is further guaranteed.
(4) The invention is suitable for testing the interlayer normal tensile strength of all composite materials.
Drawings
FIG. 1 is a diagram showing a process for preparing a test piece according to the present invention.
FIG. 2 is a schematic diagram of the critical dimensions of a PTFE membrane.
FIG. 3 is an assembly drawing of a test piece and a test apparatus according to the present invention.
In the figure:
1. layering the upper part of the composite material; 2. Layering the lower part of the composite material; 3. A polytetrafluoroethylene film; 4. A test piece;
5. a test zone; 6. A thin film hollowed-out area; 7. A metal block; 8. And a load transmission joint.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The invention provides a method for testing the interlayer normal strength of a composite material, which comprises the following steps:
in the first step, a film is prepared.
The membrane is made of 100mm x 100mm square polytetrafluoroethylene material. The thickness of the film is thin enough under the premise of process allowance, so that the completeness of the film can be ensured in the preparation process, the interface strength of two sides of the hollow area can be ensured not to be weakened, and the thickness is usually about 20% of the theoretical thickness of a single layer of the measured composite material. The film contains an annular hollow area corresponding to the composite material test area. As shown in fig. 1 and 2, the hollowInner and outer diameters R of the empty zone1、R2And the spoke width w needs to be adjusted according to the situation, so that the bonding peel strength sigma of the composite material and the metalMNStrength σ of the adhesive itselfcohAnd the interlayer normal phase strength estimated value sigma of the composite material to be measuredn estimationIn this regard, it is also influenced by the manufacturing process conditions and is necessary to ensure that the test is broken at the predetermined test interface. The method specifically comprises the following steps:
wherein sigman estimationThe transverse tensile strength of the unidirectional ply of the same material can be used for estimation; strength σ of the adhesive itself in generalcohIs larger than the bonding peel strength sigma of the composite material and the metalMNIf the binder used is relatively weak, i.e. σcoh≤σMNThen, will be σ in the formulaMNSubstitution as sigmacoh。
And secondly, preparing a test piece.
The test piece is a square plate block body with the thickness of 100mm multiplied by 100mm, as shown in figure 1, in the paving process, a polytetrafluoroethylene film 3 which does not cover a test area is inserted between a composite material upper layer 1 and a composite material lower layer 2 of a preset test interface, and then the polytetrafluoroethylene film is solidified and molded to form the test piece 4.
And thirdly, preparing a testing device and testing.
As shown in fig. 3, the test device includes two metal blocks 7 with through holes and two load transmission joints 8, and the end surfaces of the two metal blocks 7 are respectively bonded to the upper and lower surfaces of the test piece 4. One end of each of the two load transmission joints 8 is connected with the testing machine, and the other end of each of the two load transmission joints is connected with the two metal blocks 7 through holes in the metal blocks 7. And applying unidirectional tensile load to the two side load transmission joints 8 at the speed of 2mm/min until the test piece 4 is subjected to interlaminar failure, and recording the failure load P (unit is N). After the test is finished, the adhesive on the surface of the metal block 7 is removed, and the testing device can be repeatedly used under the condition of ensuring the adhesive quality.
Fourthly, the interlayer normal direction pulling of the composite materialTensile Strength σnAnd (3) calculating:
wherein, the inner and outer diameters R of the upper ring of the film1、R2In units of mm, σnIn Mpa.
Claims (1)
1. A method for testing the normal strength between layers of a composite material comprises the following two steps,
firstly, preparing a film and a test piece;
the shape and the size of the test piece and the film are the same, the test piece is a composite material to be tested, a polytetrafluoroethylene film which does not cover a test area is inserted between an upper layer and a lower layer of the composite material to be tested, and then the polytetrafluoroethylene film is cured and molded;
secondly, testing the interlayer strength of the composite material by using a testing device;
the testing device comprises two metal blocks with through holes and two load transmission joints, the end faces of the metal blocks are respectively bonded with the surfaces of an upper layer and a lower layer of the test piece, one ends of the two load transmission joints are respectively connected with the testing machine, and the other ends of the two load transmission joints are respectively connected with the two metal blocks through the through holes in the metal blocks; applying unidirectional tensile load to the two side load transmission joints until the test piece is damaged between layers, recording the damage load P with the unit of N, and calculating the normal tensile strength sigma between layers of the composite materialn；
The prepared test piece is a square flat plate block, a polytetrafluoroethylene film (3) which does not cover a test area is inserted between a composite material upper layer (1) and a composite material lower layer (2) of a preset test interface in the paving process, and then the test piece (4) is prepared by curing and molding;
the method is characterized in that:
the film is made of 100mm square polytetrafluoroethylene material, the thickness of the film is 20% of the theoretical thickness of the single layer of the tested composite material, the film contains an annular hollow area corresponding to the test area of the composite material, and the inner part and the outer part of the hollow area on the filmDiameter R1、R2Adjusted according to the situation, the adhesive peel strength sigma of the composite material and the metalMNStrength σ of the adhesive itselfcohAnd the interlayer normal phase strength estimated value sigma of the composite material to be measuredn estimationIn relation to the above, the method for ensuring the test to be damaged in the predetermined test interface specifically comprises the following steps:
wherein sigman estimationEstimating the transverse tensile strength of the unidirectional ply of the same material; strength σ of the adhesive itself in generalcohIs larger than the bonding peel strength sigma of the composite material and the metalMNWhen is σcoh≤σMNWhen it is, then the formula is expressed as sigmaMNSubstitution as sigmacoh；
The interlaminar normal tensile strength sigma of the composite materialn：
Wherein, the inner and outer diameters R of the annular hollow-out area on the film1、R2And the width w of the spokes on the film is in mm, sigmanIn MPa.
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| CN108548719B true CN108548719B (en) | 2021-03-30 |
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| CN109406270B (en) * | 2018-10-08 | 2021-05-07 | 上海海洋大学 | Heterogeneous multidirectional EVA foam tensile strength test method for ocean buoy floating body |
| CN110907609A (en) * | 2019-12-24 | 2020-03-24 | 中国航空工业集团公司西安飞机设计研究所 | Performance verification method of composite material |
| CN111272650A (en) * | 2020-03-02 | 2020-06-12 | 广西师范大学 | Joint for testing failure criterion of composite material bonding structure |
| CN115290597B (en) * | 2022-10-08 | 2023-03-17 | 首都师范大学 | Terahertz technology-based method and system for detecting coating adhesion-free defect |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN201355343Y (en) * | 2008-12-24 | 2009-12-02 | 中国航空工业第一集团公司北京航空制造工程研究所 | Tensile specimen for testing bonding strength of coating |
| CN104316403A (en) * | 2014-10-21 | 2015-01-28 | 英业达科技有限公司 | Extension test method |
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| CN202256126U (en) * | 2011-09-23 | 2012-05-30 | 潍坊汇胜绝缘技术有限公司 | A clamp for testing interlayer engagement intensity of cardboards |
| CN102680330B (en) * | 2012-05-11 | 2014-03-19 | 中国航空工业集团公司西安飞机设计研究所 | Composite interlaminar shear performance testing method |
| CN105486632A (en) * | 2015-12-28 | 2016-04-13 | 银邦金属复合材料股份有限公司 | Measuring method for bonding strength of metallic composite, sample and sample manufacturing method |
| CN105758791B (en) * | 2016-03-01 | 2019-03-29 | 银邦金属复合材料股份有限公司 | Device and method, sample and the sample production method of metallic composite interface bond strength measurement |
| CN206772698U (en) * | 2017-05-16 | 2017-12-19 | 西安锐思博创应用材料科技有限公司 | A kind of composite interlayer testing device for shear strength |
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| CN201355343Y (en) * | 2008-12-24 | 2009-12-02 | 中国航空工业第一集团公司北京航空制造工程研究所 | Tensile specimen for testing bonding strength of coating |
| CN104316403A (en) * | 2014-10-21 | 2015-01-28 | 英业达科技有限公司 | Extension test method |
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