US2677271A - Apparatus for testing materials having plastic flow characteristics - Google Patents

Description

Ma 4 1954 R. B. FARIS, JR. ETAL y APPARATUS FOR TESTING MATERIALS HAVING 2677271 PLASTIC FLOW CHARACTERISTICS Filed May 6, 1950 E I 5 v o. D I 2 g 5 2 Q f g '1 3 N 5 v a I%;

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INVENTORS P015597 5. FA /?/5 J2, MEL V/N M F/NK, HARE/SON M Sa VE, HARLEY E HAADMAN MFM 47'TOP/YEX5 Patented May 4, 1954 APPARATUS. FOR TESTING MATERIALSv HAVING PLASTIC FLOW CHARACTER- ISTICS Robert B. Faris, Jr.,.Solon, Harley F. Hardman, WicklifleyHarrison M. Stine, East Cleveland, and Melvin- M. Fink, Parma, Ohio, assignors to The Standard. (ZIilv Company, Cleveland, Ohio,

a corporation of .Ohio

Application May 6, 1950, Serial No. 160,546

3 Claims.

In testin strength of' materials by: force applied at an intermediatepoint to a: test piece or bar resting on two spacedknife edge supports-,.the apparatus now commonly in use is of the; impact form and the shock-loading form; In the impact type of apparatus, a high force is applied instantaneously, and'the energy required to break the sample is determined; or this instantaneous force isincreased and successively applied until the test piece is broken. In the shock-loading type, weights are. applied; being added in succession until the load breaks the sample. In both of these, the characteristic is that there is not a constant rate of application of pressure, nor a constant-rat test of deforms ability. Materials for some usages, and some kinds of materials could be more satisfactorily tested if the deformation undergone were at-a constant rate. In thepresent invention, a constant drive rate is applied to the test sample, and it becomes possible to determine deformability under high constant rate of deformation applition, as well as to determine breakage behavior or" materials generally; Other objects and advantages will appear from thefollowin description.

To the accomplishment of the foregoing and related ends, saidinvention then comprises the features hereinafter fully described and particularly pointed out in the'claims, the following description and the annexeddrawingsettingforth in detail certain illustrative embodiments of the invention, these being indicative, however; of" but a few of the various ways in which the-princip1e of the invention may be employed.

In said annexed drawing, the sole figure is a side elevational, partly schematic showing of apparatus in accordance with the invention.

The sample or piece to be-tested is supported on knife-edge-type spaced supports, and an opposed intermediate edge is forced against the piece at a constant high rate of speed; As illustrated in the drawing, the testpiece I is supported on edges '2, 3, and an opposed edge 4- at an intermediate point is forced-against th test piece by high speedconstant rate-means. In the illustration, this is shown as a hydraulic cylinder 5 and piston 6 supplied with" a pressure fluid, for instance oil, from a reservoir 7 by-a constantdrive pump 8. The supply line 9'to the cylinder proceeds through a selector valve Ill, which when turned one way ports the flow oi'oil through the pipe II to the cylinderbeneaththe-piston and at the same time ports an exhaust through pipe I 2 and pipe I 3 f i'omthe-otherend of the cylinder back to the reservoir; and, vice versa, when: the selector valve is turned the other way, it ports the flow of oil through pipe I2 to the cylinder abovelthe pistonv and at the same time ports oil back from beneath the piston through pipe I I and pipe I3 to the reservoir. Additionally, a relief valve I5 is provided in the pip 9, this being of the well known type which, set to a predetermined pressure, will allow return of oil from the cylinder through pipe I! back to the reservoir. Thus, with the selector valve I0 set tofeed pressure fluid into the cylinder below the piston, the piston is raised to the top, while fluid thereabove is exhausted back to the reservoir 1, and then when the piston is in its uppermost position, the mounting pressure will" exceed the set-point for the relief'valve I5, which then diverts the surplus fluid' back to the reservoirthrough pipe I'I, maintaining the piston in-position.

The lower end of the piston rod 20 has secured toit, asby a nut 2|, an elliptical flat band spring 22, and opposite to the end of the piston, the edge member 4 is similarly secured to the band, as by anut 23. The nuts 2! and 23 engage the respective portions of elements 20 and 4 which pass through holes in thespring band. Interposed between the end of the piston and the edge memher 4 is a coil spring or booster spring 25, which normally holds the edge member and piston end and elliptical sprin in predetermined relationship, but which on application of pressure to the piston allows a slight compression of the elliptical band 22; To indicate the force or stress ap plied, the elliptical spring 22 is provided with strain gauges 21-, 28, these being of any suitable or known commercial form whose resistance varies with the suriacedeformation of the object to which they are attached, e. g. he aldwi Locomotive Company strain gauge. They are in electric circuits with a dual Wheatstone bridge and voltage amplifiers which operate suitable indicating-means. Conveniently this may be an oscillograph to givea-permanent record of the test. Engaging a collar is on the piston rod 20, and movable therewith is the end of a flat spring 3|, whose other end is anchored at a fixed point, such as post 32 by a nut 33; This spring also carries strain gauges 34 above and below, and these are'in circuit with the dual Wheatstone bridge and amplifiers and dual indicator or oscillograph. This arrangement measures the amount of motion of the movable edge member.

.Thecharacteristics of the instrumentation are such as to give: instantaneous and continuous stress stra-m. relationships. Thus, the application of dimensional data allows a calculation of moduli of elasticity and rupture as well as ultimate deformability.

The electrical circuits shown-in the apparatus diagram consist of two entirely independent electrical channels, each starting with a Wheatstone bridge containing strain gauges and ending in a recording pen of an oscillograph. In the top circuit, two 1,000 ohm resistance wire strain gauges 34 are placed in two arms of the Wheatstone bridge in such a manner that any influence which afiects both gauges alike produces no unbalance of the bridge, while opposite influences, such as compression of one and tension of the other, produce twice the unbalance which would be caused if a single gauge were used. The use of these gauges as sensing elements is such that the quantity being measured always influences the two gauges oppositely while changes such as temperature affect both gauges alike and cause no output. Variable resistors 35 and 36 are coarse and fine bridge balancing controls, while the switch 31 allows the operator to choose one of the three unity-ratio arms 38 such that the bridge will have maximum sensitivity. (Maximum sensitivity occurs when all four arms of a bridge have equal resistance.) Switch 40 and resistor 39 allow the introduction of a small, reproducible unbalance into the bridge for calibrating purposes. The battery 41 supplies a direct current voltage to the bridge, and this supply voltage is regulated in steps by switch 42 and continuously over the range between steps by the variable resistor 43. Switch 44 permits the galvanometer 4'! to be switched into one or the other bridge circuits to aid in balancing or to disconnect the galvanometer entirely. Switch 45 and resistor 46 provide a shunt for the galvanometer so that its sensitivity may be reduced. The output of the bridge is fed to a direct current amplifier 48,-the output .of which is fed to ink-pen oscillograph channel 49 of a dual channel oscillograph D. The sensitivity and calibration of this entire circuit is con trolled by the supply voltage and the amplifier gain. In practice, the system is calibrated statically by using a known input to the gauges and recording the deflection of the oscillograph pen. At the same time, the deflection caused by operating switch 40 is recorded. At any subsequent time the system can be re-calibrated by adjusting the supply voltage and amplifier gain so that the previously recorded deflection of the os cillograph pen is obtained when switch 40 is operated.

The lower circuit operates in exactly the same manner as the upper with the exception of the way in which the strain gauges are used. In this case, it was not possible to obtain two opposite forms of the quantity to be measured, so only one arm of the bridge contains an active gauge. However, a dummy gauge is used for the other arm. A dummy gauge is one which is subjected to as many extraneous influences affecting the active gauge as is possible (such as temperature, humidity, etc.) so that these influences will still tend to cancel in the bridge circuit.

In making a test, the pump 8 is started, this forcing a constant rate of flow of oil in the line 9. The selector valve Ill being set to divert the fluid through pipe I l, the piston is raised. Then, the test piece T is positioned on the support edges 2, 3. Such piece may be of dimensions suitable for the character of the material tested,and by adhering to dimensions standardized for each general kind of material, comparative results are obtained. The piston 6 having reached the top of the cylinder, the building pressure opens the relief valve l5 and the excess fluid re-circulates through pipe I! back to the reservoir 1. By now turning the selector valve ID to feed the pressure fluid through pipe [2 to the top of the cylinder the piston 6 is forced down, and at the same time the fluid from below the piston is exhausted through pipes H and I3 back to the reservoir 1. As the knife edge 4 strikes the test piece, the springs 25 and 22 slightly compress, and the strain gauges 21, 28 indicate the force applied, and the strain gauges 34 indicate the distance travelled by the piston. Rates of deformation appropriate to the materials will of course be employed, the rate being determined by the speed of the pump drive. In each instance, the displacement of the sample, and of the hydraulic piston, is proportional to the flexing of the flat spring 31. This flexing is then translated into change of resistance of the two attached strain gauges, and from there, by the instrumentation to the oscillograph deflections. The force applied to the sample is measured by the change in resistance of the strain gauges attached to the elliptical spring loop. The working range is determined by the characteristics of the intermediate spring 25. Springs of suitable moduli may be substituted for any desired working range of deformability. As the test occurs in such a short fraction of a second, temperature control housing is unnecessary. Some materials may be first adjusted to temperature desired and then be placed in the testing apparatus. For instance, some materials may be preliminarily refrigerated. Others may be tested at ordinary temperature.

An essentially straight line relationship exists between thickness of the sample and deformation. Deformability results can thus be reported as per cent of sample thickness.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We therefore particularly point out and distinctly claim as our invention:

1. In testing apparatus having spaced supporting edges to support a piece to be tested and a movable opposed edge member to apply force at a point intermediate said spaced edges and an element movable through a range equal to the movement of the piece tested and electric translating and viewing means; the combination of a constant drive pump, a reservoir supplying the pump with fluid, a piston and piston rod operated by fluid from said pump, an elliptical spring forming the sole means hold-ing said movable opposed edge member to the end of said piston rod, a collar on the piston rod to move therewith, a flat spring having one end engaging in said collar, 2. fixed anchorage to hold the other end of said flat spring, strain gauge resistances on said elliptical spring, strain gauge resistances on said flat spring, circuits including the respective resistances, and a pair of indicating means one operated by the circuit from the elliptical spring and the other operated by the circuit from the .flat spring.

2. In testing apparatus having spaced supporting edges to support a piece to be tested and a movable opposed edge member to apply force at a point intermediate said spaced edges and an element movable through a range equal to the movement of the piece tested, and electric translater and viewing means; the combination of constant speed force applying means having a rod, an elliptical spring forming the sole means holding said movable opposed edge member to an end of said rod, a collar on said rod to move therewith, a flat spring having one end engaging said collar, a fixed anchorage to hold the other end of said flat spring, distortion-affected resistances on said elliptical spring, distortionaffected resistances on said flat spring, circuits including the respective resistances, and a pair of indicating means one operated by the circuit from the elliptical spring and the other operated by the circuit from the flat spring.

3. In testing apparatus having spaced supporting edges to support a piece to be tested and a movable opposed edge member to apply force at a point intermediate said spaced edges and an element movable through a range equal to the movement of the piece tested and electric translating viewing means; the combination of a constant speed force applying means having a rod, an elliptical spring forming the sole means holding said movable opposed edge member to the end of said rod, a flat spring having one end anchored and the other movable with the constant speed force applying rod, an electric circuit controlled by said elliptical spring translating its movement into terms of force, an electric circuit controlled by said flat spring translating its movement into space-traversing terms, and a pair of indicators each controlled by one of said circuits.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,827,805 Watts Oct. 20-, 1931 2,081,598 Peters et a1. May 25, 1937 2,346,981 Manjoine et a1. Apr. 18, 1944 2,386,989 Summers Oct. 16, 1945 2,423,867 Zener et al. July 15, 1947 2,426,390 De Forest Aug. 26, 1947 2,487,681 Weisselberg Nov. 8, 1949 2,504,985 Kallas et al Apr. 25, 1950 FOREIGN PATENTS Number Country Date 121,013 Great Britain Dec. 5, 1918 587,096 Great Britain Apr. 14, 1947 OTHER REFERENCES Oil and Gas Journal, vol. 42 #4, June 3, 1943, p. 43.

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