Multiaxial tension

On the other hand, San Miguel and Duran (Ref 125) showed that the mechanical properties of polyurethane solid proplnt were degraded significantly by gamma irradiation dosages greater than 106 R. The tests used to determine the effects were by swelling, torsion, uniaxial tension and multiaxial tension... 

In order to describe the viscoelastic behavior of a system subjected to multiaxial tensions, it is convenient to separate the shear (deviatoric) effects from the purely dilatational components. This is due to the fact that in... 

CONSTITUTIVE EQUATIONS IN DIFFERENTIAL FORM FOR MULTIAXIAL TENSION STATES... 

Multiaxial tension Applies stretch on two axes perpendicular to each other. Gupta etaL (2008)... 

ASTM D5617 Standard Test Method for Multiaxial Tension Test for Geosynthelics DIN 61551 Geosynthetics Determination of Burst Strength This test is more commonly used to test geomembranes, but permeable materials such as GTXs may also be tested in conjunction with an impermeable material. The procedures of different standards vary a lot. A common volume-controlled test would be preferable (Table 7.13 and Fig. 7.18). 

Figure 16 illustrates several test specimens which have been used (46) in the multiaxial characterization of solid propellants. The arrows indicate the direction of load application. The strip tension or strip biaxial test has been used extensively in failure studies. It can be seen that the propellant is constrained by the long bonded edge so that lateral contraction is prevented and tension is produced in two axes simultaneously. The sample is free to contract normal to these axes. The ratio of the two principal tensile stresses may be varied from 0 to 0.5 by varying the bonded length of incompressible materials. 

Uniaxial tensile criteria can lead to gross inaccuracies when applied to situations where combined stresses lead to failure in multiaxial stress fields. Often one assumes that combined stresses have no influence and that the maximum principal stress governs the failure behavior. An improved approach applied to biaxial tension conditions relies upon a pragmatic biaxial correction factor which is applied to uniaxial data,... 

In a recent attempt to bring an engineering approach to multiaxial failure in solid propellants, Siron and Duerr (92) tested two composite double-base formulations under nine distinct states of stress. The tests included triaxial poker chip, biaxial strip, uniaxial extension, shear, diametral compression, uniaxial compression, and pressurized uniaxial extension at several temperatures and strain rates. The data were reduced in terms of an empirically defined constraint parameter which ranged from —1.0 (hydrostatic compression) to +1.0 (hydrostatic tension). The parameter () is defined in terms of principal stresses and indicates the tensile or compressive nature of the stress field at any point in a structure —i.e.,... 

A polymer is more likely to fail by brittle fracture under uniaxial tension than under uniaxial compression. Lesser and Kody [164] showed that the yielding of epoxy-amine networks subjected to multiaxial stress states can be described with the modified van Mises criterion. It was found to be possible to measure a compressive yield stress (Gcy) for all of their networks, while the networks with the smallest Mc values failed by brittle fracture and did not provide measured values for the tensile yield stress (Gty) [23,164-166]. Crawford and Lesser [165] showed that Gcy and Gty at a given temperature and strain rate were related by Equation 11.43. 

Further work will be focusing on lifetime prediction methods for gas turbine materials (superalloys) and experiments on fracture mechanics in superalloys as well as finite element calculations of multiaxial loaded tubes and validation of multiaxial tests (tension, torsion, internal pressure). 

After the optimal set of maferial paramefers was found, the same parameters were then used to simulate the small pimch test. This validation simulation was performed to check the capability of the HM to predict a multiaxial deformation history. It is well known that many constitutive models can predict uniaxial deformation histories relatively well, but that it is significantly more difficult to accurately predict multiaxial deformation states. It has been shown, for example, that the /2-plasticity model can accurately predict monotonic imiaxial tension or compression data for UTTMWPE, buf is very poor at predicting cyclic or multiaxial deformation states (Bergstrom, Rimnac, and Kurtz 2003). 

Professor S. Suresh of Brown University visited GAPD In December 1989, to present recent developments in cyclic fatigue, cyclic compression fatigue pre-cracking, and mixed-mode fracture testing of ceramics. Professor Suresh will be contracted to perform mixed-mode I III fracture toughness tests of notched cyclic compression pre-cracked tension-torsion specimens, and multiaxial strength tests on unnotched tension-torsion specimen. 

Fig. 10.4 Shear creep compliance curves for pure torsion and torsion with superimposed tension or compression for PMMA. Change in creep compliance with multiaxial load test illustrates interaction nonlinearity (Lu and Knauss, (1999) reprinted with kind permission from Springer Science and Business Media).

Many other important impact design parameters such as yield stress, energy to yield, initial modulus, and deformation at break can be measured with high-speed tension tests (38). In spite of the capability of high-rate tension tests to provide stress at strain rates that simulate actual service, the tests have not been popular because the delivered stress is uniaxial. Normally, the real-life impact stress is multiaxial. 

Steel Under Earthquake Excitations Reinforcing steel in external reinforced crmcrete jackets for the retrofit and strengthening of existing reinforced concrete or steel members comes mainly in the form of bars. Usually, the stress-strain behavior under tension-compression is cmcial to assess the longitudinal bars contribution. The stress-strain behavior under tension is of interest for the transverse reinforcement (stirmps). Steel dowels and stud shear connectors may involve shear (or tensile) behavior of steel- or bond-related issues. External steel plates may be considered under multiaxial loading (i.e., in cases of shear strengthening in order to estimate their yield stress). Bond-related issues may concern bar-concrete interfaces, bar-resin-concrete interfaces (NSM applications), or plate-resin-concrete interfaces under cyclic loading. 

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