Search

The dynamic behaviour of different materials has been widely studied using the split Hopkinson pressure bar (SHPB) testing. The striker bar's velocity (SV) and the incident bar's impact surface are well known to have a significant impact on producing a clear signal in the compressive SHPB studies. Several times, the shape of the incident strain signal differs from an ideal state, and the reason is difficult to find. In this paper, a parametric investigation of such understudied instances is carried out utilising Abaqus software for finite element analysis (FEA). The numerically obtained incident strain pulse for a perfectly aligned SHPB setup with different SV was validated experimentally on compressive SHPB apparatus. The numerical output was found to have good agreement with experimental results. Further, plots of incident strain were evaluated numerically for Sv (10, 15, 20, 25 and 30 in m/s) which was used for polynomial fitting using MATLAB's curve fitting tool. A similar method was adopted for symmetrically plane non-parallel impact surface on the incident bar. The angles chosen for FEA calculations were 5°, 10°, 15° and 20°. Filleted impact surface with radius (r) 1.5, 3, 4.5 and 6 mm was also studied. The study of the variation of impact surface shape was done at a striker velocity of 25 m/s. It was observed from this study that when striker velocity increases, the absolute magnitude of incident strain at peak increases while rise time remained constant. In turn, when the symmetrically non-parallel plane surface angle and fillet radius grow, the absolute value of incident strain at peak almost stays the same but the rising time lengthens. This study can help understand the nature and discrepancy of the incident strain signal obtained in the compressive SHPB setup and find its root cause. [ABSTRACT FROM AUTHOR]

In this article, the effect of pristine and carboxyl functionalized carbon nanotube (CNT and FCNT) reinforcement on the durability of glass fiber-reinforced epoxy (GE) composite has been assessed under repeated hydrothermal cycling (HC) and compared with that of control GE composites. Each HC constitutes of 24 h conditioning in a water bath maintained at 15 °C followed by further 24 h water aging at 50 °C. Control GE, 0.1 wt % pristine CNT-embedded GE (CNT-GE) and 0.1 wt % FCNT-embedded GE (FCNT-GE) were exposed to 20, 40, and 60 number of HC in order to assess their durability. Initially, for a lower number of HC, FCNT-GE composite was found to have the best water resistance followed by CNT-GE and GE composites, whereas after 40 and 60 number of HC, the trend got modified. Flexural testing was conducted to evaluate the durability of these composites upon 20, 40, and 60 number of HC. Also, the degree of recovery in the flexural properties of the composites after 60 number of HC was evaluated by conducting desorption process. The cyclic changes in water bath temperature caused interfacial debonding at the CNT/matrix interface resulting in accelerated water absorption and reduced flexural performance. The water absorption by the composites had deleterious effect on their glass transition temperature (Tg) and matrices chemical bonding. The variation in the failure modes in these composites, before cycling and after 60 number of HC, was compared using SEM analysis. [ABSTRACT FROM AUTHOR]

A compressive split Hopkinson pressure bar (SHPB) apparatus is utilised for the high strain-rate investigation of symmetrical epoxy-based carbon/glass (CGE) and carbon/Kevlar (CKE) hybrid composite samples along the through-thickness direction. The stacking sequence used for the hybrid composites was [C5/G5]S and [C5/K5]S. Compared to the density of neat epoxy-based carbon (CE) composite, the density of CGE composite was about 14% higher, whereas the density of CKE composite was about 8% lower. An initial striker velocity of about 25 m/s was used for all experiments. The mean reference strain rate observed for CGE and CKE hybrid composites was 2293 and 2333 s−1, respectively, with a negligible difference in mean compressive strength. The mean strain to failure of [C5/K5]S was almost 17% higher than [C5/G5]S, and proper stress equilibrium was observed. This article presents the significant outcomes of SHPB testing, including mechanical response and failure analysis of the hybrid composite samples. [ABSTRACT FROM AUTHOR]

This article deals with the influence of titanium dioxide (TiO2) and graphene nanoplatelet (GnP) on epoxy's tribological, compressive, surface hardness and thermal response. Initially, the TiO2 and GnP particle morphology was analyzed. A ball-on-disc testing apparatus was used to evaluate the wear and frictional behavior of the nanocomposites. The worn-out surface micrographs of tested nanocomposite samples were analyzed using a scanning electron microscope (SEM). The compressive response of the nanocomposite samples was analyzed at in-situ temperatures of 30, 75 and 120°C. The hardness of the nanocomposite sample's surface was also examined, along with the influence of nanofiller addition on samples' glass transition temperature (Tg). The elemental-colored mapping was used to verify the proper dispersion of the nanofiller in the epoxy. It was observed that the inclusion of 2 phr (per hundred resin) by weight of TiO2 along with 2 phr GnP showed a decrement of 65.17% in wear volume and an increase of 17.37% peak compressive stress value at 30°C compared to neat epoxy. An increment in the Tg was also observed with the inclusion of nanofillers in epoxy. Significant outcomes of the study conducted on the nanocomposite samples are discussed in this article. [ABSTRACT FROM AUTHOR]

The interlaminar shear strength (ILSS) of the fiber-reinforced polymer (FRP) composites is critical in structural applications. At the same time, glass transition temperature Tg determines the degree of crosslinking, which depends majorly on post-curing temperature and time. In this study, the post-curing parameters (time and temperature) are initially varied to analyze their effect on the ILSS and Tg values of the Kevlar/epoxy (KE) laminated composite samples. For optimizing post-curing parameters, the temperatures selected were 70, 140, 210, and 280°C and time designated was 3, 6, and 9 hours. It was found that the KE sample post-cured at 140°C for 6 hours retained its aesthetic properties and gave an optimized result without any sign of over-curing. Further, graphene nanoplatelet (GnP) was added to KE composites (KE-GnP) in 0.25, 0.5 and 1.0 wt % of epoxy. ILSS characterization of KE-GnP was done at 25°C and in-situ elevated-temperature environments of 70, 100, and 140°C. Tg values were also evaluated. A polynomial surface was generated using the curve fitting toolbox of MATLAB from the ILSS data points obtained. Energy-dispersive X‑ray (EDX) spectroscopy was used to observe GnP dispersion uniformity in the matrix. Significant outcomes of the investigation are discussed in this paper. [ABSTRACT FROM AUTHOR]

Carbon fibre-reinforced polymer (CFRP) composites have evolved as one of the most reliable materials for critical structural applications. Electrophoretic deposition (EPD) is one among the most opted routes to carry out the surface modification of carbon fibre (CF). Methyl violet (MV) is used in the cathodic EPD technique to maintain stability of suspension and to impart positive charge to the nanofillers thereby facilitating the cathodic EPD. In the current research work, the authors have deposited graphene carboxyl (G–COOH) on CF surface via cathodic EPD route, and an attempt was made to analyse the impact of MV on the mechanical behaviour of the modified CFRP composite by carrying out flexural and short beam shear tests. The G–COOH/CFRP composite in which MV was removed with acetone washing has shown an improvement of 21.93% and 10.89% in interlaminar shear strength (ILSS) and flexural strength (FS), respectively, in comparison to neat CFRP composite. However, G–COOH/CFRP composite in which the MV was not washed has shown a decrement of 20.82% and 3.21% in ILSS and FS in comparison to neat CFRP composite, respectively. High-resolution transmission electron microscope was used to observe the morphology of graphene carboxyl, and scanning electron microscope was used to carry out fractography analysis to comprehend the failure mechanism and dominant failure mode. Fourier transform infrared spectroscopy analysis was carried out to understand the effect of methyl violet on the epoxy/nanofiller interface chemistry. [ABSTRACT FROM AUTHOR]

Advanced fiber-reinforced polymer composites are stronger, durable and lighter than their metallic counterparts. Inter-ply hybrid polymer composites are formed by more than one type of fiber plies reinforced in the same matrix. The durability and integrity of the altered stacking sequence and hybrid ratio of such composites at low temperature conditions have not been widely explored. In this research work, flexural behavior of cryogenic conditioned glass and/or carbon fibers-based hybrid composites has been studied. Substituting two glass fiber plies with those of carbon on the top side of glass/epoxy (GE) composite, denoted as (C2G3), achieved the maximum flexural strength of 491.94 MPa (27.82% higher than unconditioned neat GE composite) after 8 h of conditioning, and the highest flexural modulus of 33.52 GPa was attained by C1G3C1 composite. A detailed analysis of the effect of conditioning duration and stacking sequence of the hybrids on the flexural properties was done and the underlying mechanisms were discussed. Post-failure analysis of composites using a scanning electron microscope was done to understand the fractographic behavior of the samples. Finally, elemental analysis was used to measure nitrogen incorporation within the matrix as a function of conditioning duration. [ABSTRACT FROM AUTHOR]

The economical nanoclay/polymer nanocomposite with laudable thermal and barrier properties motivates scientists for its potential exploration in widespread engineering applications. The present investigation has been focused on the mechanical durability study of these nanocomposites at above ambient temperature environment. In-situ flexural testing was performed on epoxy based nanocomposites with 0, 0.5, 1 and 3 wt% nanoclay content at various temperatures (30, 50, 70 and 90 °C). Addition of only 0.5 wt% nanoclay in epoxy resulted in 17 and 26% improvement in flexural strength and modulus respectively (which is maximum among all the materials), when tested at room temperature, due to highest degree of exfoliation of nanoclay as confirmed from XRD analysis. At higher testing temperatures, all the materials exhibited a decreasing trend in their mechanical properties and a positive reinforcement effect was evident even up to the close vicinity of glass transition temperature. These findings were further verified by dynamic mechanical thermal analysis in a wide range of temperature varying continuously from 40 to 200 °C. The degree of dispersion and possible deformation and failure mechanisms were identified by scanning electron microscope. [ABSTRACT FROM AUTHOR]