PSI - Issue 14

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

834

5

transmitted strain by the working principle of the strain gauge. Using Eq. (1) – (3), the specimen strain rate, strain, and stress are determined. Before the testing of the final composite specimen, the SHPB set-up was calibrated for its accuracy in accordance with the scheme suggested in the literature by Naik et al. (2008). 3.2. Effect of moisture on stress-strain behavior of UHMWPE-SR composite The strain rate effect on the stress-strain behavior of dry and wet conditioned UHMWPE-SR composite specimens through the thickness direction is shown in Fig. 2. The stress-strain behavior of dry UHMWPE-SR composite specimen for strain rates variation in the range of 2105 s -1 to 4220 s -1 is depicted in Fig. 2 (a). With increasing strain rates the stress-strain curve rises in terms of both the slope of the curve and the peak stress attained by the specimen. This is corroborated in the known literature by Asija et al. (2017). At low striker bar velocity, the strain rate developed in a dry UHMWPE-SR composite specimen is low, owing to lower incident energy. For every one of the estimations of strain rate below 4000/s, the specimen after the test were recovered intact, with insignificant macroscopic failure. Subsequent higher loading uncovered a sharp rising stress curve, until the point that the peak stress is accomplished for a given incident energy. It may be noted for all the stress curves that after attaining a peak of stress the curve follows a path tangent to strain axis, until the completion of stress wave as depicted in Fig. 2 (a). This type of material behavior is well suited for trapping of an object moving at high velocities, like a projectile. The peak strain recorded for UHMWPE-SR composite is 0.28. The strain rate of 4050/s, served as the extreme breaking point of the rate of loading at which composite specimen was recovered without macroscopic damage. For compressive loading rates over 4050/s strain rate, the composite specimen experiences perceptible damage. The plainly visible harm is noted as delamination of the specimen. Nonetheless, it might be noticed that the composite attained a peak stress of 457 MPa when the specimen was broken into two pieces because of delamination. Any further increment in incident energy brings about further damage. The significance of damage is delineated as numerous delamination destinations alongside cracked strands. The same isn't the situation until the point of limiting strain rate. At limiting strain rate one piece of the composite is delaminated into two pieces. A thin layer of filaments hauled out of lamina was seen under this extreme loading condition. Subsequently, there was no compelling reason to additionally enhance the rate of loading.

(a)

(b)

2105 2832 3540 4050 4220

2110 2336 2553 3160 3730

100 150 200 250

0 100 200 300 400 500

Stress (MPa)

0 50

Stress (MPa)

0

0.1

0.2

0.3

0

0.1

0.2

0.3

Strain

Strain

Fig. 2: Stress versus strain plot for UHMWPE-SR composite (a) dry and (b) wet. Fig. 2 (b) reveals the effect of moisture ingestion on the stress-strain behavior of UHMWPE-SR composite. For identical loading rates, a significant difference in stress-strain behavior of dry and wet UHMWPE-SR composite is noted in Fig. 2. Though the initial loading curve for wet composite follows the trend of rising stress with a growing rate of loading, the peak stress attained by the wet UHMWPE-SR specimen is nowhere comparable to dry composite specimen. The wet composite specimen never revealed significant constant stress growth of strain as a function of strain rate. Also, the peak stress and strain attained by wet composite are much lower compared to dry composite. The peak stress and strain attained by the wet UHMWPE-SR composite are 210 MPa and 0.23, respectively. It’s