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

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

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

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

Performance of aluminium/vinylester particulate composite

The performances of aluminum/vinylester particulate-composites were studied in detail in order to investigate its suitability for engineering applications. This study examined the suitability of atomised aluminum particles for particulate reinforcement of a vinyl ester resin. Mechanical properties were obtained for the composite by testing various percentages of aluminium powder (75-150 μm) and vinylester resin. It has been found that the inclusion of Al powder has not significantly changed the properties of vinylester resin, however an improvement in the ductility of the composite has been recorded. The optimal performances of the composite were exhibited by 15% Al composition. The properties of the particulate composites were modeled using numerous empirical models. Unfortunately a significant difference was found between some of the experimental and predicted properties of the Al/vinylester particulate composite. This paper intends to detail the variation of mechanical properties with the change of Al volume fraction in the composite and the performances of empirical models in prediction of the properties of particulate composites

Investigation of embedded near infrared fibre Bragg grating (FBG) sensors (830 nm) in structural health monitoring of glass fibre composite structures

The transmitted spectrums of conventional FBG sensors operating in near infrared region (Bragg wavelength ~ 830nm) embedded in E-Glass/Vinylester composite sample were investigated at static and after fatigue loading. Also transmitted waveforms of a FBG attached to a surface of single layer E-Glass/Vinylester composite sample which has a purposely created hole closer to attached FBG sensor were examined in order to understand the FBG response in a vicinity of a void/damage, under static loading situation. As a consequence, some conclusions were made on the sensitivity and durability of the use of FBG sensors fabricated by conventional writing techniques in long term health monitoring system of composite structures

A study of estimation of damage accumulation of glass fibre reinforce plastic (GFRP) composites under a block loading situation

Many cumulative damage theories have been used in lifetime calculation of GFRP composite components. However, it is well known that linear damage accumulation models are inadequate for predicting the cumulative damage in GFRP compositeas due to their dominant viscoelastic characteristics. This paper discusses the outcomes of application of damage accumulation models proposed by Palmgren-Miner [Miner MA. Cumulative damage in Fatigue. J Appl Mech 1945;12(September):A159–64], Broutman and Sahu [Broutman LJ, Sahu SA. New theory to predict cumulative fatigue damage. In: Fiberglass reinforced plastics, composite materials: testing and design (second conference), ASTM STP 497; 1972. p. 170–88], Hashin and Rotem [Hashin Z, Rotem A. A cumulative damage theory of fatigue failure. J Mater Sci Eng 1978;(34):147–60] and Epaarachchi and Clausen [Epaarachchi Jayantha A, Clausen Philip D. On predicting the cumulative fatigue damage in glass fibre reinforced plastic (GFRP) composites under step/discrete loading. Composites Part A: Appl Sci Manuf 2005;36(9):1236–45], to calculate the lifetime of GFRP composite samples under repeated block loading situations

Effects of static–fatigue (tension) on the tension–tension fatigue life of glass fibre reinforced plastic composites

The effects of static–fatigue interaction on tension–tension fatigue life of glass fibre reinforced plastic (GFRP) composites were investigated. This paper proposed a new static–fatigue model, which is capable of predicting residual strength after a period of static loading. Also an algorithm is proposed to calculate fatigue lives with the inclusion of static–fatigue interaction. Predictions from the proposed static–fatigue model show a good agreement with the experimental results. Static–fatigue interaction has shown a considerable effect on fatigue lives of GFRP composites at intermediate and lower applied stress levels possibly due to a longer exposure to applied loads. At higher load levels approximately greater than 65% of ultimate stress, and higher stress ratios range like 0.5 < R < 0.9, fatigue lives shown to be closer to material’s static–fatigue limits which is shorter than the expected lifetime by cyclic fatigue

Assessment of damage accumulation in Glass Fibre Reinforced Plastic (GFRP) composites under spectrum fatigue loading

Assessment of lifetime under spectrum-fatigue loading was undertaken on GFRP composites material, using cumulative damage models proposed by Palmgren-Miner, Broutman & Sahu, Hashin & Rotem and Epaarachchi & Clausen. None of the models were not performed well. Epaarachchi & Clausen model which is based on reisdual strength has the flexibility of applying according to assumed damage accumulation mechanisms. This model consistently predicting conservative lifetime while the other models almost over predicting. Further, a statistical analysis perform on predictions has shown that the Epaarachchi and Clausen model is performing better than the other models

A study on estimation of damage acumulation of glass fibre reinforced plastic (GFRP) composites under a block loading situation

Many cumulative damage theories have been used in lifetime calculation of GFRP composite components. However, it is well known that linear damage accumulation models are inadequate for predicting the cumulative damage in GFRP compositeas due to their dominant viscoelastic characteristics. This paper discusses the outcomes of application of damage accumulation models proposed by Palmgren-Miner [Miner MA. Cumulative damage in Fatigue. J Appl Mech 1945;12(September):A159–64], Broutman and Sahu [Broutman LJ, Sahu SA. New theory to predict cumulative fatigue damage. In: Fiberglass reinforced plastics, composite materials: testing and design (second conference), ASTM STP 497; 1972. p. 170–88], Hashin and Rotem [Hashin Z, Rotem A. A cumulative damage theory of fatigue failure. J Mater Sci Eng 1978;(34):147–60] and Epaarachchi and Clausen [Epaarachchi Jayantha A, Clausen Philip D. On predicting the cumulative fatigue damage in glass fibre reinforced plastic (GFRP) composites under step/discrete loading. Composites Part A: Appl Sci Manuf 2005;36(9):1236–45], to calculate the lifetime of GFRP composite samples under repeated block loading situations