Mechanical properties and thermomechanical behaviour of poly (ethylene-co-vinyl acetate) based shape memory polymer composites

Shape memory polymers (SMPs) are an emerging class of intelligent material that can program in to a temporary shape and recover to its original by exposing to a particular external stimulus. Poly (ethyleneco-vinyl acetate) (EVA) is one of the commercial polymers, which has been used to produce SMPs activated by heat. However, its low mechanical properties, low recovery stress and flexible behaviour restrict the potential applications under robust conditions. Herein, we developed a series of EVA based shape memory polymer composites (SMPCs) with glass fibre, carbon fibre and multi-walled carbon nanotube reinforcements. The effects of different reinforcements on tensile strength have been investigated. Moreover, the dynamic mechanical analysis has been carried out to characterize the glass transition temperature. The shape memory performance of the neat SMP and SMPCs were examined by measuring the angle recovery of 90° bended strips. Subsequently, the shape fixity and recovery ratios of the samples were calculated. This paper presents the manufacturing methods and performance of the fibre and particle reinforced EVA based SMPCs. The inclusion of reinforcements have enhanced the applicability of EVA based SMPCs in wider range of engineering application. In this paper the applicability of such SMPCs for machine elements are deliberated. Accordingly, a conceptual design of a SMPC made mechanical coupler is presented

Effect of the foam embellishments on the pedestrian safety of the vehicle front protection systems

Pedestrian safety related compliance requirements are very important in case of design and development of the vehicle front protection systems. Computer aided engineering impact simulations were carried out to evaluate Head Injury Criterion (HIC) of a typical bullbar impacting it with an adult headform and correlated with experimental results. Impact simulations were carried out on the same bullbar covered with semi‐rigid polyurethane foam to study the effect of foam embellishments on the pedestrian safety. Results obtained from the impact simulations were presented in this paper

Modal analysis of high frequency acoustic signal approach for progressive failure monitoring in thin composite plates

During the past few decades, many successful research works have evidently shown remarkable capability of Acoustic Emission (AE) for early damage detection of composite materials. Modal Analysis of AE signals or Modal Acoustic Emission (MAE) offers a better theoretical background for acoustic emission analysis which is necessary to get more qualitative and quantitative result. In this paper, the application of MAE concept in a single channel AE source location detection method for failure characterization and monitoring in thin composite plates was presented. Single channel AE source location is one of the recent studies for composite early damage localization, owing to the growing interest and knowledge of modal analysis of AE wave. A tensile test was conducted for glass fiber epoxy resin specimen with small notch. A single channel of AE system was used to determine the AE source location on specimen under testing. The results revealed that AE single channel source location provides reasonable accuracy for glass fiber laminate which was tested

Detection and characterisation of delamination damage propagation in woven glass fibre reinforced polymer composite using thermoelastic response mapping

This paper details a study on the application of Thermoelastic Stress Analysis (TSA) for the investigation of delamination damage propagation in glass fibre reinforced composite materials. A woven Glass (0/90)/ Epoxy composite sample containing a purposely created delamination was subjected to a step-cyclic loading (varying mean level) whilst monitoring the thermoelastic response of the sample with an infrared camera. A finite element analysis (FEA) was performed using cohesive elements to simulate the propagation of the delamination under a monotonically increasing axial load. It is shown that the delamination crack length inferred from the TSA results is consistent with microscopic analysis of the sample, and that the measured crack growth rate is in reasonable agreement with simulation results

Carbon fibre reinforced shape memory polymer composites for deployable space habitats

Intelligent material shape memory polymers (SMPs) and their composites are capable of memorizing and recovering the original shape upon exposure to a particular external stimulus. This paper presents the mechanical properties, thermomechanical behaviour and the shape memory characteristics of 0/90 woven carbon fibre reinforced shape memory composite. The results revealed that the superlative mechanical properties of carbon fibres as a reinforcement has enhanced the strength of the SMP composite (SMPC) to be applicable for space engineering innovations. Furthermore, the recovery behaviour of 90º bended SMPC specimens have been investigated by exposing to heated air and near infraredradiation. Both stimulus methods have shown almost 98% shape recovery. In addition, a model of a cubic deployable structure has been fabricated and respective shape programming and recovery behaviours have been investigated based on the enclosed volume. Interestingly, the deployable structure has been programmed in to almost three times smaller volume and very nearly recovered to its original shape under vacuumed conditions. Accordingly, the carbon fibre reinforced SMPCs can be used to produce deployable space habitats to fabricate on earth, compress and pack in a spacecraft, transport to an outer space location and ultimately deploy in to the original shape

Effect of a nano-fibrous structure on the nanofiber mat's hydrophobicity

To improve hydrophobicity, both low surface energy and proper surface roughness are necessary. In this research, the possible surface roughening effect of PET nanofibers was applied to manipulate an appropriate surface topography for the mat composed of them while a fluorocarbon layer generated low surface energy

An Investigation of Acoustic Emission Signal Attenuation for Monitoring of Progressive Failure in Fiberglass Reinforced Composite Laminates

Glass fiber reinforced polymer (GFRP) laminates have a high damping characteristic which can retard ultra-high frequency guided wave signals from propagating along the plate. Owing to this, the identification of an effective area for sensor location is essential. Appropriate signal processing, including wavelet analysis was done, in order to observe the details of an acoustic emission (AE) signal which was emitted at a distance from it source. This study reveals that it is necessary to consider the near field and far field effects of AE signal attenuation, in particular, to determine a composite's micro failure characterization. Consequently, this attenuation behavior was used to develop the non-velocity based source mapping to monitor the progressive failure in composite laminates. This paper details the outcomes of the signal energy attenuation method with an improved algorithm for progressive failure monitoring in fiberglass reinforced composite laminates and the 'effective length' for better AE detection

Fabric Parameter Effect on the Mechanical Properties of Woven Hemp Fabric Reinforced Composites as an Alternative to Wood Products

Hemp is a common natural fibre which has reliable properties and is available in the forms of staple fibres, yarns and fabrics. However, less works were done by using woven hemp fabric in composite materials, especially for an alternative to wood products. In this work, woven hemp fabrics in different fabric layering orientations have been used to reinforce vinyl ester resin by employing hand lay-up method. The properties of hemp fabric were used to investigate how these properties can affect the physical and mechanical behaviour of the fabricated composites. The results show that fabric properties and layering orientations contribute to the tensile, flexural and impact properties of the composites. Based on the comparison to wood and engineered wood products’ properties, the mechanical properties of composites are found to be comparable. The comparison also shows that the woven hemp fabric reinforced vinyl ester can be an alternative for wood and engineered wood products in building industries especially in low-load bearing applications

Damage onset analysis of optimized shape memory polymer composites during programming into curved shapes

The unique shape memorizing ability of shape memory polymers (SMPs) and their fibre reinforced composites have offered the prospect of remedying challenging, unsolved engineering applications. Interestingly, research integrating deformable shape memory polymer composites (SMPCs) in prefabricated modular constructions, deployable outer space structures and other compactable structural components have emerged in the recent past. To ensure effective use in strength demanding applications, SMPC components must possess better mechanical properties. Increased fibre content in SMPCs will improve mechanical properties but can adversely affect the shape memory effect (SME), increasing the possibility of material damage when programming into curved shapes and bends. This will degrade the strength capacity of SMPCs in their applications. This paper details a complete study performed on this critical effect optimizing SMPC properties by means of a 3×3 Taguchi array. The study also provides an experimental framework demonstrating how these undesirable effects can be mitigated coupled with an ABAQUS finite element analysis (FEA) damage prediction strategy. Interestingly, the compression side of the specimen was found to be the most critical location prone to programming damage. In addition, a compressive stress level of 70 MPa was found to be the damage onset stress (σo) point for programming using FEA, and correlated with experimental results. The proposed experimental and FEA framework will enhance future SMPC component design, allowing researchers to predict the possibility of programming damage numerically, saving time and cost. We believe that these findings will aid researchers seeking to develop strong and efficient functional SMPCs for future engineering applications

Flammability characteristics of chemical treated woven hemp fabric reinforced vinyl ester composites

In the present work, the treatments using sodium hydroxide, flame retardant chemical and combination of both sodium hydroxide and flame retardant changed the physical properties thus reduced the mechanical properties of woven hemp fabric and fabricated composites. However, the treatments increased the fire retardant properties of fabricated composites as indicated by the burning tests, thermogravimetry analyses and limiting oxygen index tests. An assessment based on woods and engineered wood products have shown that the fabricated composites are suitable to be used for building infrastructure materials as an alternative to wood products