PSI - Issue 14

Hemant Chouhan et al. / Procedia Structural Integrity 14 (2019) 830–838 Author name / Structural Integrity Procedia 00 (2018) 000–000

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worthy to note here that, as per NIJ standards the compressive high rate experimentation was done within one hour of removal of a specimen from the potable water bath at 21  C; yet depending on the time lapsed before the compressive loading of specimen, a variation in stress-strain behaviour of the specimen was also noted. Hence, it may not always be feasible to get an identical trend of stress-strain curve for the wet composite specimen. Based on SHPB experimentation, the compressive high strain rate behavior of UHMWPE-SR based composites might be partitioned into three classifications. The main classification has a place with the study bringing about the flawless specimen without significant damage on impact. The second classification includes just a single strain rate which brings about peak stress at the main event of a naturally visible damage as delamination. The third class includes experimentation performed above the strain rate recorded in the second classification bringing about the higher specimen destruction beyond recognition. Consequently, the third classification is of very little utilization. As the composite specimen will damage well before attaining these higher stresses, revealed by these higher strain rates of loading. It may also be noted that the damage was depicted primarily in the form of delamination for both the dry and wet composite. However, it was only the highest rates of loading wherein the dry composite underwent delamination, on the contrary, the wet composite experienced delamination at all the rates of loading, except the lowest strain rate. 4. Phenomenological modeling of compressive high strain rate test results Three-dimensional representation of high strain rate test results can serve as a visual aid in interpreting the mechanical behaviour of materials complex behavior. Fig. 3 depicts the 3D plots of dry and wet UHMWPE-SR composite. It can be easily understood that the stress of an elastic material will depend only on the strain, therefore a 3D representation of this behavior will resemble a surface  = f(  ). Likewise, the rate dependent material behavior can be represented as  = f( ̇ ). On similar lines, an elastic-perfectly viscoplastic solid (Bingham-Norton Model) or elasto-viscoplastic hardening material will be represented as  = f(  , ̇ ).

Fig. 3. Three-dimensional representation of SHPB test results of UHMWPE-SR composite (a) dry and (b) wet specimen.

The initial studies of material behaviour were attempted with the power-law model, which has been commonly used to describe the composites behavior under high strain rate loading.  =A  m (4) Here, A and m are strain rate dependent nonlinear parameters and both are typically determined experimentally. A and m are further represented in the form of the power law in the literature by Ravikumar et al. (2013). This form of the mathematical model is well suited for a composite system undergoing brittle fracture or the one not undergoing significant strain growth at constant stress. Yet it’s worth noting that the initial loading of any solid material system will always be elastic in nature. Hence, an initial loading curve should follow Eq. (4), with different