Strain measurements, fatigue analysis

The foregoing analysis of the skin-doubler specimen shows that it is essential to know the stiffness characteristics of the adhesive. Since good design practice places bond lines in shear, it was decided that the shear modulus is the primary stiffness parameter. Furthermore, it is recognized that more than the initial portion of the shear stress-strain curve was required. It was clear that the total curve was not linear. It was anticipated that the nonlinearity portion would bear heavily on creep and fatigue performance. Accordingly, the primary requirements for the strain measuring device were set as follows ... 

The analysis of the processes leading to the degradation of solids and various materials is of interest in many different aspects. These include the analysis of the properties of materials, the nature and character of the stressed state, and the means by which loads are applied. The latter include testing using constant strain rates, creep analysis, measurements of stability with loads applied over extended periods of time, resistance to impact, cyclic fatigue, and many others. Numerous standard test methods were developed for various materials under different conditions. The influence of the specific conditions, such as temperature, humidity, and the presence of surface-active substances also represents the subject of essential studies. Depending on the particular combination of all these factors, a particular type of material degradation can be observed. 

The SN-curve is a line in the Oamp-N-plane (N is a measure of number of cycles to failure, S is a general symbol referring to stress, strain, load, displacement etc. In this case, S denotes aamp). When constant-amplitude fatigue data are available for the material, an SN-curve can be found using regression analysis of the test data. Usually, it is appropriate to... 

The outputs from finite element analysis will tell the chemist many of the important predictive characteristics of the part. The effects of load (stress, strain, and deflection) are measured. Material selection based on strength and part dimensions and tolerances are determined and easily adjusted. The effects of heat (heat transfer and thermal stresses) are determined as well as material selection based on conduction and insulation. Special applications such as bending and vibration characteristics, crashworthiness, fatigue, and noise can be determined. The design requirements, such as expected loads, load cycle cost, mass targets, and budget targets, can be predicted and met with proper application of the FEA tool. 

Polybutadienes with vinyl contents of 10 7 and 72.4% have been selected for further fatigue-to-failure analysis. Fatigue life measurements have been performed on a large number of specimens by means of the Fatigue-to-Failure Tester (Monsanto). Carbon-black-filled compounds with 50 phr N330 carbon black were cured with conventional curing system at 145°C. Curative levels have been chosen to obtain vulcaniza-tes at several levels of 300% modulus. Fatigue tests were performed on un-notched specimens at room temperature and at several deformation amplitudes. Data discussed here were obtained at 136% strain amplitude. 

Work by Schapery, Saxena, Wilhams, and others details the analysis of cracks in creeping, strain rate dependent materials, and provides a predictive basis for the apparently brittle nature of FCP in UHMWPE [43-48]. Particularly usefid are the models developed by Schapery and Wilhams, which directly link the intrinsic, constitutive viscoelastic relaxation behavior of the material to the advance of a stable crack tip [46,48]. The power of these models is the predictive nature of the mechanics in relating ECP dynamics to the material s viscoelastic behavior that is eashy measured in a simple one-dimensional creep test The elementary consequences of the models result in the static mode fatigue crack propagation behavior that is observed in UHMWPE, and thus potentially provide a first-principles explanation of the fatigue and fracture behavior by the material. 

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