Method of single-axis cyclic test of material

FIELD: test equipment.

SUBSTANCE: invention refers to material test methods. Essence of the invention: a sample is first strained to the maximum set deformation, held in this deformation for a given time, compressed to the initial unloaded state, left in it for a given time, with further cyclic deformation with delays in each deformation stage of compression and tension, where at each tension cycle the set deformation is less than at the previous cycle, and the set deformation at each unloading cycle is larger than in the previous cycle.

EFFECT: more information on material properties from a sample test, new information represented by equilibrium stress-strain curve, dissipation loss, material softening after each tension/compression cycle, and relaxation curves together with material structure recovery curves for various deformations.

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The invention relates to methods for testing of materials.

Known a method in which the cyclic stretching with increasing deformation of the sample, first along one axis, then along the second axis (see Dargazany R., Itskov M. A network evolution model for the anisotropic Mullins effect in carbon black filled rubbers // International Journal of Solids and Structures. Elsevier, 2009. V. 46. P. 2967-2977. - http://www.elsever.com/locate/ijsolstr)

A method is known in which the cyclic uniaxial stretching with increasing deformation, and at each level of deformation of the sample cycloneda many times (see J. Diani, M. Brieu, P. Gilormini Observation and modeling of the anisotropic visco-hyperelastick behavior of a rubberlike material // International Journal of Solids and Structures. Elsevier, 2006. V. 43. P. 3044-3056. - http://www.elsever.com/locate/ijsolstr)

The known method, where the sample cycloneda by complex cycle: with decreasing amplitude of the deformation in comparison with the previous loading with increasing amplitude of discharge (see Netzker Husnu S. D., M. Kaliske An andochronic plasticity formulation for filled rubber // International Journal of Solids and Structures. Elsevier, 2010. V. 47. P. 2371-2379. - http://www.elsever.com/locate/ijsolstr)

The above methods have a common drawback, namely, the failure information when testing a single sample.

The closest in technical essence and the achieved technical result of the proposed solution is a method of cyclic tests described in [Rickaby S. R., Scott N. H. A cyclic stress softening model for the Mullins effect // Intrnational Journal of Solids and Structures. Elsevier, 2013. V. 50. P. 111-120. - www.elsever.com/locate/ijsolstr] when the sample is repeatedly stretched to a predetermined deformation, and then compressed to the initial position at a constant speed.

In Fig.3 prototype presented cyclically loaded and unloaded rubber sample, which is pre-stretched from P0to P1to the point P1where the deformation λ=λmaxwhich is reached at time t. Stress relaxation occurs at time t1, then unloading from P1to P0to the initial load P0when the voltage becomes zero and the time t2. Then stretch again before deformation λ=λmax. Then again remove the load of the second cycle of deformation to the initial load P0that occurs at time t2*. This process of reducing the previous voltage when the same deformation continues and unloading during the second cycle (the process of softening of the material during subsequent cycles under the same strain). Reduce stress and possibly with further cycles of loading-unloading, i.e., t1*-t1and t2-t1* may be unequal.

The disadvantage of the prototype method is the small amount of information obtained about the properties of a material are determined by the maximum stress� in each cycle of elongation, time stretching to a predetermined deformation in each cycle and the time compression to achieve zero load. Is determined by the degree of softening of the material during each cycle of stretching and permanent deformation upon unloading in every cycle tension-compression.

The task of the invention is to obtain more information about the properties of the material when tested one sample, obtaining new data. This prevents the spread of data received due to manufacturing errors and capture various samples and save material and time trials.

The problem is solved by the features specified in the 1st paragraph of the claims, in common with the prototype, such as the method of uniaxial cyclic test material comprising uniaxial cyclic tension-compression with a constant given speed, to a predetermined deformation, and distinctive essential features, such as the first sample is stretched to a predetermined maximum strain, maintained at the specified time warp, shrink to its original condition, to withstand the specified time, then cyclically deformed with a dwell time at each step of deformation in tension and compression, the deformation in each cycle of stretch is set smaller than in the previous cycle, and the deformation at each cycle of discharge�. more than in the previous cycle. According to claim 2 of the formula of the invention, the sample at each cycle dilate at different rates of deformation. Distinctive features of the proposed method - stop and exposure time at each stage of deformation (this allows you to remove the temporal characteristic of the material) and the construction of the equilibrium curve; also the tension on each cycle at different speeds.

The above set of essential features allows to obtain the following technical result - obtaining more information about the properties of the material when tested per sample, as well as obtaining new information - the construction of the equilibrium curve stretching, dissipative losses, the softening of the material after each cycle tension-compression and relaxation curves and recovery curves of the structure of the material under different strain.

The invention is illustrated in the example and pattern. The method is carried out in the following sequence, namely by the initial deformation of the sample to a predetermined maximum deformation of the test sample, the exposure time when this strain for the process of stress relaxation, unloading of the sample at the same rate to its original status, exposure time to restore the internal structure of the material, the secondary stretching treatment�CA to the same maximum strain and exposure time for stress relaxation, compression of the sample before deformation corresponding to non-zero voltage and exposure time when this strain in the third cycle tension-compression tensile strain is set smaller than the maximum deformation at the 2nd cycle, the dwell time and unloading to the deformation, greater than it was in the second cycle, and again the exposure time to restore the structure of the material.

Further Cycling occurs before deformation, each time smaller than in the previous cycle, unloading to the deformation, greater than the previous cycle. At each given level of deformation of the specimen is subjected to exposure time. The number of cycles is not installed - the more, the more the points to construct the equilibrium curve is obtained.

The drawing shows a graph of the Cycling test, and indicate the equilibrium point of the curve. Under equilibrium curve means the curve is very slow stretching of the sample when it has all viscoelastic processes and associated stress relaxation is absent. Thus, when the deformation of the elastomeric composite of long polymer molecules slide along the surface of the carbon filler in the tension of the material. When the load is removed, the molecules return to their original state, but the process is much slower than in tension depends on the adhesion on�kernich fibers with the surface of the carbon and the mobility of molecules i.e., the temperature of the sample. This explains the presence of viscoelasticity in rubbers filled with carbon black.

The value of the viscoelasticity depends on the polymer and the degree of filling it with carbon. The unfilled elastomer viscoelasticity is missing, the higher the content, the viscoelasticity above.

To construct the equilibrium points of the curve you need to take the point of the restored structure of the material after its exposure time when unloading at each cycle and the end point of the stress relaxation after exposure time when the tensile specimen. The first point of the equilibrium curve on the x-axis is taken in the place of its intersection with the graph of discharge on the first cycle of tests.

This graph also shows the hysteresis material (dissipative) losses in tension-compression at each cycle of deformation of the compression.

In the drawing the graphs of cyclic loading where you can see the softening of the material during each cycle of deformation - the torque curve at each subsequent cycle is below the previous loading.

All charts are constructed on the computer using the data file is tested, in which there are columns with the current time, applied force, displacement.

To explore the properties of the material at different speeds on each cycle of loading is applied in different RMS�spine deformation.

An example for a cyclic test material on the proposed programme:

1. Elongation up to 100%, and wait 20 min. Speed 100%/min.

2. Return to the start position and wait 20 min. Speed 100%/min.

3. Elongation up to 100% and wait 10 min. Speed 100%/min.

4. Unloading of up to 15% and wait 10 min. Speed of 50%/min.

5. Elongation to 90% and wait 10 min. Speed of 50%/min.

6. Unloading to 22% and wait 10 min. the Speed of 20%/min.

7. Elongation of 80% and wait 10 min. the Speed of 20%/min.

8. Unloading up to 35% and wait 10 min. the Speed of 5%/min.

9. Elongation up to 70% and wait 10 min. the Speed of 5%/min.

10. Return to the starting position. The speed of 5%/min.

Thus, according to the invention is obtained the equilibrium curve stretching, dissipative losses, the softening of the material after each cycle tension-compression and relaxation curves and recovery curves of the structure of the material under different strain, and determine the dependence of the mechanical behavior of the material from warp speed.

1. Method uniaxial cyclic test material comprising uniaxial cyclic tension-compression at a given speed to a predetermined deformation, characterized in that the first sample is stretched to a predetermined maximum strain, maintained at the specified time warp, shrink to its original unloaded state, stand ass�TES the time then cyclically deformed with a dwell time at each step of deformation in tension and compression, the deformation in each cycle of stretch is set smaller than in the previous cycle, and the deformation at each unloading cycle is set higher than in the previous cycle.

2. A method according to claim 1, characterized in that the sample at each cycle dilate at different rates of deformation.



 

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