Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Nanoindentation creep of tin and aluminium: A comparative study between constant load and constant strain rate methods

Abstract: Creep properties of polycrystalline Tin (Sn) and single crystal Aluminium (Al) were studied by two nanoindentation methods, i.e., constant load (CL) test and constant strain rate (CSR) test. The indentation strain rate and stress were calculated as the analogies drawn from uniaxial creep analysis. The stress exponent was expressed as the slope of the strain rate–stress curves plotted in the double logarithm scale. Between the two testing methods, the CSR test was clearly shown to be able to detect the creep of Sn in the power-law region, where the grain size had little effect on the creep rate. However, it was found that steady-state creep could not be achieved in the CL test. This has imposed ambiguities in applying the creep analysis developed from conventional creep scheme. The creep displacement from CL test was found unrepeatable for multiple measurements. CL test also has a smaller accessible stress range than that from a CSR test. The gradual variation of the stress exponents, especially for the small grain Sn sample, during holding process in the CL test could be due to the participation of the other rate controlling mechanisms which were closely related to the non-steady-state creep behaviour.

The rheology of highly concentrated PBLG solutions

Abstract: We have characterized the rheology of two concentrated, liquid crystalline solutions of poly(γ benzyl–L–glutamate) of molecular weight 238 000 in m–cresol. Comparing these results to previous work on less concentrated, liquid crystalline solutions separates the effects of concentration from the direct influence of defect texture on liquid crystal polymer rheology. This work also defines the limitations of current polydomain models and suggests improvements. The solution at C=37wt% PBLG behaves similarly to moderately concentrated nematic solutions (12wt%

Creep and creep fracture in hot-pressed alumina

Abstract: The creep and creep fracture behavior of two hot-pressed aluminas are presented, for both flexural and tensile testing. Steady-state power-law creep is observed with a stress exponent of about 2 for each material. Three distinct fracture regimes are found. At high stress in flexure, fracture occurs by slow crack growth with a high stress dependence of the failure time. At intermediate stresses, in both flexure and tension, creep fracture occurs by multiple microcracking after modest strains. Failure times exhibit a modest stress dependence (stress exponent of 2.5 in tension and 3 in flexure), with a constant failure strain equal to 0.09. The failure times are considerably longer in flexure than in tension, because of the constraint imposed on crack growth by the bending geometry. We conclude that flexure cannot be used for creep lifetime assessment, even in simple, single-phase materials such as Al2O3. At low stresses, in tension, failure also exhibits a modest stress dependence but with a much higher failure strain. The material shows the onset of super-plastic behavior.