Mechanical quasi-static-loading

Thus, from the known density pb the measured wave speeds Cl and Cs, the elastic constants E and v can be determined. It is noted that the values are given at a high frequency associated with the ultrasound pulse used. The use of these properties at quasi-static loading conditions requires postexamination in order to evaluate whether the aerogel has frequency-or rate-dependent mechanical behavior. 

The methodology of integrative simulation is already established for quasi-static loading conditions [3]. The approach for an integrative crash-simulation is the same in general, but differs from the quasi-static case in the mechanical testing needed for material data determination as well as in the implementation of the local anisotropies into FEA. The approach as a whole is presented in fig. 2 and will be described in the following. 

Flinn et al. [30] describes an experimental impact technique in which <100)-oriented LiF single crystals ( 8 ppm Mg) are loaded in a controlled manner and the multiplication of screw dislocations is measured. The peak shear stress in this relatively soft material is 0.01 GPa. For shear impulses exceeding approximately 40 dyne s/cm, dislocation multiplication is adequately described by the multiple-cross-glide mechanism [(7.24)] with m = l/bL = (2-4) X 10 m, in reasonable agreement with quasi-static measurement [2]. 

Testing Conditions and Analysis. The fracture behavior was investigated at room temperature at nominal piston velocities, from 10-4 m/s to 10 m/s. For test speeds higher than 10-1 m/s, the damped test procedure described in reference 15 was used. Quasi-static stress conditions therefore prevailed in the specimen, even at high loading rates. This fact allowed the analysis of fracture-mechanics parameters to be performed using a static approach. 

For certain products long time dynamic (creep, fatigue, impact, etc.) mechanical load performances in different environments are required. Dynamic loading in the present context is taken to include deformation rates above those achieved on the standard laboratory-testing machine (commonly designated as static or quasi-static just reviewed). These slower tests may encounter minimal time-dependent effects, such as creep and stress-relaxation, and therefore are in a sense dynamic. Thus the terms static and dynamic can be overlapping. 

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