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

Response Fibre Bragg Grating (FBG) strain sensors embedded at different locations through the thickness around a delamination in a composite lamina

A few FBG strain sensors were embedded at a vicinity of delamination of a laminated composite plate. Reflected spectra of FBG sensors which located in the same layer as the delamination and one layer above the delamination were investigated in order to understand the change of the reflected spectra due to stress concentrations at the delamination. The reflected waveforms of sensors were broadened with the increase of loading, as expected. A considerable difference in the response of two sensors was observed during both uniaxial and flexural loading. These differences show that the FBG sensors are capable of capturing the precise nature of the delamination under various loading conditions. Further, these observations provide evidence of the feasibility of using FBG sensor responses obtained from various locations allows the location of the delamination to be determined. This paper details some new and interesting findings of the use of spectral shapes and strain measurements from embedded FBG sensors in damage detection

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

Use of FBG sensors for SHM in aerospace structures

This paper details some significant findings on the use of the fiber Bragg grating (FBG) sensors for structural health monitoring (SHM) in aerospace fiber reinforced polymer (FRP) structures. A diminutive sensor provides a capability of imbedding inside FRP structures to monitor vital locations of damage. Some practical problems associated with the implementation of FBG based SHM systems in the aerospace FRP structures such as the difficulty of embedding FBG sensors during the manufacturing process and interrelation of distortion to FBG spectra due to internal damage, and other independent effects will be thoroughly studied. An innovative method to interpret FBG signals for identifying damage inside the structures will also be discussed

Viscous criterion and its relation with the projectile-thorax energy interactions

Despite many injury criteria to measure thoracic trauma in known engineering parameters, viscous criterion, that is a product of maximum instantaneous velocity of thorax deformation and maximum instantaneous chest compression, has been widely used. Using Lobdell mathematical model of the thorax, Wang [1] has carried out analytical studies and proved that peak viscous response is related to the peak energy storing rate of the thorax and also proved that it does not related to viscosity of the thorax. Authors have carried out a scholastic study by impacting a FE model thorax MTHOTA (Mechanical THOrax for Trauma Assessment), which is fully validated for blunt ballistic impacts, with a foam nose projectile with speeds of 30 – 90 m/s with an increment of 5 m/s. VCmax values and projectile – thorax energy interactions were evaluated and presented in this paper. From the outcome of the simulations, relation between maximum stored energy

Evaluation of the blunt thoracic trauma due to baseball impacts – review of the Blunt Criterion

Evaluation of the thoracic injury due to blunt impacts during the contact and collision sports activity is crucial for the development and validation of the chest protectors and safety solid sports for the athletes. In the case of young athletes, proper chest protectors can avoid not only severe chest trauma but also protect them from the sudden death due to commotio-cordis. In order to evaluate the thoracic injury in terms of known engineering parameters (Viscous Criterion), non-linear finite element simulations were carried out by impacting FE model of the thorax surrogate (MTHOTA- Mechanical THOrax for Trauma Assessment) with a synthetic baseball and a synthetic baseball of the same size and weight at the impact speed of 10 – 45 m/s (with an increment of 5 m/s). Synthetic baseball and soft-core baseball produced VCmax = 1 m/s at the impact speed of 27.9 m/s and 30.7 m/s respectively. For both sports ball impact cases, Blunt Criterion (which is commonly used as non-lethal munitions design criterion that takes only kinetic energy of the projectile and weight & geometry of the thorax into consideration) was evaluated for all impact cases of two types of baseballs. Results have revealed the projectile specificity of the Blunt Criterion

Effect of energy absorbing mechanisms on the blunt thoracic trauma caused by ballistic impacts

military and law enforcement officials have been using kinetic energy non-lethal weapons ranging from rubber bullets to projectiles with foam in situations which do not warrant the usage of lethal force. On many occasions, non-lethal projectiles have caused serious injuries. Therefore, a scholastic study was carried out to see the effect on the injury caused by the projectiles embedded with various energy absorbing mechanisms. Projectile – target interaction (kinetic energy transfer or energy gained by the target and Total energy of the projectile) plays a vital role in understanding the effect of the projectile on the target. Therefore, to evaluate the effect of the energy absorbing mechanisms on the blunt thoracic trauma, target considered should emulate the human thorax as far as the projectile-thorax interaction is concerned. A fully validated FE model of the thoracic surrogate (FE model of the MTHOTA surrogate of the thorax, which is validated with the human response corridors developed by Wayne State University’s researchers) was impacted with a typical foam nosed projectile at a speed of 90 meters per second. A collapsible Aluminum foil attached to the hollow foam nose of the projectile and impact simulations were carried out for different thicknesses of the foil (0.3 mm and 0.5 – 4.0 mm with an increment of 0.5 mm). To nullify the effect of the variation in the mass and also for effective comparison, impact speed was adjusted so that kinetic energy of the projectile remain same for all analyses. For the design of the collapsible mechanisms considered for the study, foil thickness less than 2 mm, though foiled structure got collapsed it didn’t absorb considerable amount of energy. More than 2 mm thickness, foil didn’t collapse properly and whole projectile acted as stiff/solid round and produced more injury. Dynamic force response, dynamic displacement response, effect of the aluminum foil on the thoracic injury in terms of VCmax etc., were presented in this paper

Review of anthropomorphic test dummies for the evaluation of thoracic trauma due to blunt ballistic impacts

Biomechanical responses of the thoraces of finite element models of 4 Anthropomorphic Test Dummies (namely, LSTC Hybrid III deformable, LSTC Hybrid III rigid, LSTC/NCAC Hybrid III and ES-2re) were reviewed by impacting them with the 140 gram wooden projectile with impact speeds of 20 and 40 m/s, and 30 g wooden projectile with 60 m/s. In order to elucidate the usefulness of the ATDs for evaluating blunt thoracic trauma caused by blunt ballistic impacts (projectile mass 20 – 200 gram, velocity 20 – 250 m/s), responses obtained were compared with the human response corridors developed by Wayne State University’s researchers. It was evident that none of the thoraces exhibited bio-fidelity for the impact cases considered for the analysis. Thoraces of former three dummies found to be very stiff and the latter yielded realistic responses but Viscous Criterion (VCmax) values based on the deflection response were way higher when compared to those obtained from the cadaveric experiments for the similar impact conditions. Values of viscous criterion (VCmax), probability for AIS3+ and AIS4+ injuries based on the maximum rib deflections (only for the ES-2re dummy for particular impact locations), were found to be, for some cases, to a certain extent, in agreement with those obtained from the cadaveric experiments. The present study highlights the unsuitability of the numerous thorax models (both physical and finite element), while necessitating the development of the thorax surrogate with an acceptable biofidelity. Such biomechanical surrogate of the thorax, for the evaluation of trauma, is essential for the validation of non-lethal ammunition, development of bullet proof vests and chest protectors for the athletes of collision & contact sports

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