Presentation is loading. Please wait.

Presentation is loading. Please wait.

Experimental methods for material measurements at high strain-rate Lorenzo Peroni, Massimiliano Avalle Dipartimento di Meccanica, Politecnico di Torino.

Similar presentations


Presentation on theme: "Experimental methods for material measurements at high strain-rate Lorenzo Peroni, Massimiliano Avalle Dipartimento di Meccanica, Politecnico di Torino."— Presentation transcript:

1 Experimental methods for material measurements at high strain-rate Lorenzo Peroni, Massimiliano Avalle Dipartimento di Meccanica, Politecnico di Torino Workshop on Materials for Collimators and Beam Absorbers

2 L. Peroni, M. Avalle – Politecnico di Torino 2 Contents Introduction Material behaviors, characterization Experimental methods Mechanical testing equipment Conclusions

3 L. Peroni, M. Avalle – Politecnico di Torino 3 Dynamic effects on material behavior Variation in yield strength Variation in failure strength (ultimate tensile strength) Variation in elongation at failure Different work- hardening behaviour Stress-strain characteristic and the effect of strain-rate on the mechanical behaviour of a material For many materials, strain-rate has negligible effect on the elastic modulus   Quasi-static mechanical characteristic Dynamic mechanical characteristic  s d  s s  r d  r s  r d  r s E E

4 L. Peroni, M. Avalle – Politecnico di Torino 4 Strain-rate effect: some experimental results  Different classes of polymers tested: PP, PA6, TEEE, PS, PC, EVA… PP, mechanical characteristics a f c d e b

5 L. Peroni, M. Avalle – Politecnico di Torino 5 Multiaxial behavior (plastics, foams…) Therefore, the plastic collapse condition cannot be characterized from the result of a single (uniaxial) test, having a given ratio of hydrostatic/deviatoric stress components, but it is necessary to perform several tests with different combinations of deviatoric and hydrostatic stress components As it is well known plastics and cellular materials yield is not independent on the hydrostatic component of stress  hyd Von Mises Tresca

6 L. Peroni, M. Avalle – Politecnico di Torino 6 Testing methods

7 L. Peroni, M. Avalle – Politecnico di Torino 7 Uniaxial tension test

8 L. Peroni, M. Avalle – Politecnico di Torino 8 Shear: torsion test Torsion loading test rig (shown with an aluminum foam sample mounted on it)

9 L. Peroni, M. Avalle – Politecnico di Torino 9 Shear: 4-point asymmetrical tests  xz x z Used for the mechanical characterization of ceramics, and ceramics composites (CfC’s) according to ASTM C1469 standard Foamglas

10 L. Peroni, M. Avalle – Politecnico di Torino 10 Shear strength of joinings Cu/CfC joint shear test Offset single-lap *CFC/Cu/CuCrZr and W/Cu/CuCrZr joints for ITER Shear/compression Torsion Double-notch (ASTM C1292) SiC joined by: Silicon Glass

11 L. Peroni, M. Avalle – Politecnico di Torino 11 Test chamber Fluid p Axial rod Hydrostatic tests  A =  R = p  A   R (= p) Fluid p AA Axial rod Radial rod

12 L. Peroni, M. Avalle – Politecnico di Torino 12 Hydrostatic and hydro-compression test Hydrostatic (compression) Hydro-compression

13 L. Peroni, M. Avalle – Politecnico di Torino 13 Fatigue loading Stress-life and strain-life approach Rotating bending (metals), plane bending (polymers, composites) high-cycle fatigue Tension/compression low-cycle/high-cycle fatigue (evaluation of the hysteresis of the material)

14 L. Peroni, M. Avalle – Politecnico di Torino 14 Composites  For orthotropic materials like most composites, tests at different loading angles are required to obtain the different moduli (in-plane E 11, E 22, G 12 ) and Poisson’s coefficient ( 12 )  For unbalanced layered composites, bending tests are also required  Impact tests are also performed to measure dynamic properties energy absorption capability GFRP sample with rosette to measure strain in different directions

15 L. Peroni, M. Avalle – Politecnico di Torino 15 The Split Hopkinson Pressure Bar (SHPB) Operating principle  The projectile hits the incident bar generating a compressive wave train  The wave train propagates at the speed of sound in the bars material and reaches the specimen, then: ► It is partly reflected ► Partly crosses the specimen and goes through the transmission bar  The reflected and transmitted waves are measured  By reconstruction based on the two signal the dynamic mechanical characteristic is obtained Proiectile Transmission bar Incident bar Specimen

16 L. Peroni, M. Avalle – Politecnico di Torino 16 The Split Hopkinson Pressure Bar (SHPB)  Split Hopkinson Pressure Bar (SHPB, compression test)  Split Hopkinson Tensile Bar (SHTB, tensile test) Tensile specimen Steel sheet Bulk adhesive Compression specimen Bulk adhesive Aluminum foam

17 L. Peroni, M. Avalle – Politecnico di Torino 17 Determination of the stress-strain characteristic  Time history measurement of: Average stress (specimen) Strain-rate (specimen) Strain (specimen)  Signals synchronization  Evaluation of the stress-strain characteristic

18 L. Peroni, M. Avalle – Politecnico di Torino 18 Dynamic tensile equipment: FasTENS To cover the speed range from 1 to 10 m/s, in tensile loading, in between the hydraulic systems and the SHPB, a special fast tensile equipment, pneumatically actuated, has been developed (FasTENS).

19 L. Peroni, M. Avalle – Politecnico di Torino 19 Dynamic compression: ComPULSE  Pneumatically actuated  Maximum speed up to 15 m/s  Maximum available energy 3 kJ  Load measurement with piezoelectric load cells, maximum load 220 kN  Stroke measurement with laser transducer (Keyence)  Suitable also for tensile, bending, and other tests using special fixtures

20 L. Peroni, M. Avalle – Politecnico di Torino 20 Low/high temperature testing  A climatic chamber coupled with the ComPULSE equipment, was developed for dynamical tests down to - –40°C (will be further improved to be pushed down to -80°C) and up to 100°C  The sample (or component) can be conditioned but also tested at various controlled temperatures

21 L. Peroni, M. Avalle – Politecnico di Torino 21 Concluding remarks The spectrum of mechanical tests available is very large, to cover many possibility of loading, even far beyond established standard The mechanical characterization of materials is one of the first steps in the design of high performance structures Custom testing solutions are routinely developed, and will be likely to be developed for innovative and advanced materials In most cases a single type of test is not sufficient to describe in details the properties and behaviour of an advanced material or composite

22 Experimental methods for material measurements at high strain-rate Lorenzo Peroni, Massimiliano Avalle Dipartimento di Meccanica, Politecnico di Torino Workshop on Materials for Collimators and Beam Absorbers Thank you for your attention!


Download ppt "Experimental methods for material measurements at high strain-rate Lorenzo Peroni, Massimiliano Avalle Dipartimento di Meccanica, Politecnico di Torino."

Similar presentations


Ads by Google