Loading rate sensitivity of liquid nitrogen conditioned glass fiber reinforced polymeric composites: An emphasis on tensile and thermal responses

Abstract

Glass fiber reinforced polymeric (GFRP) composites are being accepted as potential materials for ultra‐low temperature applications. The current investigation is to evaluate effect of liquid nitrogen (LN2) conditioning (for different intervals of time) on the loading rate sensitivity of tensile response of GFRP composites. In order to assess this, tensile tests of the unconditioned and conditioned specimens were carried out at different crosshead speeds viz. 1, 10, 100, 500, and 1000 mm/min. At 1 mm/min crosshead speed, an improvement of 3.33% and 7.3% ultimate tensile strength (UTS) value was observed in case of 0.25 and 1 h conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Similarly, the specimens tested at 1000 mm/min show an improvement of 11.39% and 12.02% UTS for 0.25 and 1 h LN2 conditioned GFRP composites, respectively, as compared to unconditioned GFRP composites. Effect of LN2 conditioning on crosshead speed sensitivity of modulus and strain at break are also reported. The in‐service temperature of the GFRP composite was measured using temperature modulated differential scanning calorimetry. Furthermore, dynamic mechanical thermal analyzer was used in the temperature range (40–200 °C) to correlate the mechanical and thermomechanical response of the GFRP composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45856.

Effects of fiber surface grafting by functionalized carbon nanotubes on the interfacial durability during cryogenic testing and conditioning of CFRP composites

“…This deterioration in interfacial bonding can be attributed to the composite's thermal shock due to sudden exposure from RT to LN temperature (À196 C), which led to high internal stresses. 61 For 1 h aging, stronger bonding was seen at the interface from Figure 11(c), supporting the SBS test observations. So, the composite was observed regaining its interfacial strength, which can be spotted through the diffused interfacial gap in Figure 11(c) compared to the widely spaced fiber and matrix in Figure 11(b).…”

“…The modified composites' ability to maintain their ILSS could be due to a modified interface enriched with nanofillers, which improves the mechanical interlocking and acts as a shielding layer to lower the F I G U R E 6 Short beam shear (SBS) stress-strain behavior for neat and modified CE composites at different bath concentrations (0.0, 0.3, 0.5 and 1 g/L) after conditioning in LN for (a) 0.25 h, (b) 0.5 h, (c) 1 h, (d) 6 h, (e) 12 h; and (f) superimposed inter-laminar shear strength (ILSS) values for all bath concentrations and time durations [Color figure can be viewed at wileyonlinelibrary.com] stress concentration. 64 On further soaking in LN for 6 hr, an increment in ILSS was noticed for neat CE and all the three modified CE composites compared to ILSS conditioning for 0.25 h. 61 In the CE and 0.3-FCNT-CE composites, this increment in ILSS when aged for 6 h was noticeable concerning the shear strength at RT, that is, 9.34% and 2.07%, respectively. Subsequently, the indication of improvement in shear strength further increased with the increment of conditioning time of 0.25 h to 6 h. It may result in the cryogenic hardening of the epoxy matrix.…”

“…During this thermal transition, the polymeric chains that got frozen at CT, after the sudden exposure to RT, become embrittled due to the generation of high residual stresses. 61 This micro residual stress pinches the formation of cracks in the matrix and the fiber/matrix interface. Subsequently, it leads to delamination, 62 a critical failure mode at the fiber/matrix interface, failing the composite.…”

Improvement of the liquid oxygen compatibility of epoxy via the addition of surface‐modified boehmite

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