Loading rate effect

In this chapter, we will review the effects of shock-wave deform.ation on material response after the completion of the shock cycle. The techniques and design parameters necessary to implement successful shock-recovery experiments in metallic and brittle solids will be discussed. The influence of shock parameters, including peak pressure and pulse duration, loading-rate effects, and the Bauschinger effect (in some shock-loaded materials) on postshock structure/property material behavior will be detailed. 

Boukhili, B., Hubert, P. and Gauvin, R. (1991). Loading rate effect as a function of the span-to-depth ratio in three-point bend testing of unidirectional pultruded composites. Composites 22, 39-45. 

Fig. 5.7 Macroscopic damage modes that occur during the tensile and flexural creep of fiber-reinforced ceramics. It is assumed that matrix or fiber damage is avoided during initial application of the creep load (see discussion of loading rate effects in the next section). Periodic fiber fracture can occur if the creep rate of the matrix exceeds that of the fibers. Periodic matrix fracture is common when the matrix has a higher creep resistance than the fibers. In this figure, it is assumed that initial microstructural damage is avoided during application of the creep load.

Exploratory tests with a higher loading rate of 5mm/min (maximum allowed by ISO 15024) were conducted on two SO.5/0.5 and one S2/2 specimen in order to check for indications of loading rate effects. In Fig. 6, the dashed lines show the apparent delamination resistance curves of specimens tested at a loading speed of 5mm/min, the full lines the resistance curves of the specimens tested at 2mm/min. The S2/2 specimens are represented by filled circles,... 

Jaj Jajam, K. C., Tippur, H. V. Quasi-static and dynamic fi-acture behavior of particulate polymer composites A study of nano- vs. micro-size filler and loading-rate effects. Compos. Part B -... 

K. C. Jajam, Fracture Behavior of Particulate Polymer Composites (PPCs) andlnterpen-etrating Polymer Networks (IPNs) Study of Filler Size, Filler Stiffness and Loading Rate Effects, PhD Thesis, Auburn University (2013). 

To conclude the above information on spinel, an SCG assessment and strength-probability-time prediction for long-term rehability assessment were based on the loading-rate effect of fracture-strength measurements. The parameter characterizing the slow crack-growth sensitivity suggests that FG materials are less affected. The maximum stress for a lifetime of 40 years (failure probability of 1 %) was... 

Fig. 15. Effect of vapor loading rate on gasoline working capacity...

The ramp of pressure to about 3 GPa observed in shock-loaded fused quartz has been used very effectively in acceleration-pulse loading studies of viscoelastic responses of polymers by Schuler and co-workers. The loading rates obtained at various thicknesses of fused quartz have been accurately characterized and data are summarized in Fig. 3.6. At higher peak pressures there are no precise standard materials to produce ramp loadings, but materials such as the ceramic pyroceram have been effectively employed. (See the description of the piezoelectric polymer in Chap. 5.)... 

Avoiding structural failure can depend in part on the ability to predict performance of materials. When required designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied upon previously. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. This information is supported by stress-strain behavior data collected in actual materials evaluations. 

The computational methods have replaced the oversimplified models of material behavior formerly relied on. However, for new and very complex product structures that are being designed to significantly reduce the volume of materials used and in turn the product cost, computer analysis is conducted on prototypes already fabricated and undergoing testing. This computer approach can result in early and comprehensive analysis of the effects of conditions such as temperature, loading rate, environment, and material... 

Static and dynamic property The uses of these foams or porous solids are used in a variety of applications such as energy absorbers in addition to buoyant products. Properties of these materials such as a compressive constitutive law or equation of state is needed in the calculation of the dynamic response of the material to suddenly applied loads. Static testing to provide such data is appealing because of its simplicity, however, the importance of rate effects cannot be determined by this one method alone. Therefore, additional but numerically limited elevated strain-rate tests must be run for this purpose. 

Interest in the use of syntactic foam as a shock attenuator led to studies of its static and dynamic mechanical properties. Particularly important is the influence of loading rate on stiffness and crushing strength, since oversensitivity of either of these parameters can complicate the prediction of the effectiveness of a foam system as an energy absorber. 

B. S. Griffits, K. Ritz, N. Ebblewhite, and G. Dobson. Soil microbial community structure Effects of substrate loading rates. Soil Biol. Biochem. 37 145 (1999). 

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