Imperial College London

DrHariArora

Faculty of EngineeringDepartment of Bioengineering

Honorary Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 1434hari.arora04

 
 
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Location

 

4.35Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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51 results found

Ranunkel O, Guder F, Arora H, 2019, Soft robotic surrogate lung, ACS Applied Bio Materials, Vol: 2, Pages: 1490-1497, ISSN: 2576-6422

Previous artificial lung surrogates used hydrogels or balloon-like inflatable structures without reproducing the alveolar network or breathing action within the lung. A physiologically accurate, air-filled lung model inspired by soft robotics is presented. The model, soft robotic surrogate lung (SRSL), is composed of clusters of artificial alveoli made of platinum-cured silicone, with internal pathways for air flow. Mechanical tests in conjunction with full-field image and volume correlation techniques characterize the SRSL behavior. SRSLs enable both healthy and pathological lungs to be studied in idealized cases. Although simple in construction, the connected airways demonstrate clearly the importance of an inflatable network for capturing basic lung behavior (compared to more simplified lung surrogates). The SRSL highlights the potentially damaging nature of local defects caused by occlusion or overdistension (present in conditions such as chronic obstructive pulmonary disease). The SRSL is developed as a potential upgrade to conventional surrogates used for injury risk predictions in trauma. The deformation of the SRSL is evaluated against blast trauma using a shock tube. The SRSL was compared to other conventional trauma surrogate materials and showed greatest similarity to lung tissue. The SRSL has the potential to complement conventional biomechanical studies and reduce animal use in basic biomechanics studies, where high severity protocols are used.

Journal article

Del Linz P, Liang X, Hooper P, Arora H, Pascoe L, Smith D, Cormie D, Dear JPet al., 2018, A numerical method for predicting the deformation of crazed laminated windows under blast loading, Engineering Structures, Vol: 172, Pages: 29-40, ISSN: 0141-0296

The design of laminated glazing for blast resistance is significantly complicated by the post-crack behaviour of glass layers. In this research, a novel numerical method based on a semi-analytical energy model is proposed for the post-crack behaviour of crazed panes. To achieve this, the non-homogenous glass cracks patterns observed in literature experimental and analytical work was taken into consideration. It was assumed that, after the glass crazing, further deformations would occur in the cracked edge areas, whilst the central window surface would remain largely undeformed. Therefore, different internal work expressions were formulated for each zone and were then combined in the overall model. The resulting differential equation was then solved numerically. The results obtained were compared with data from four experimental full-scale blast tests for validation. Three of these blast tests (Tests 1 to 3) were presented previously (Hooper et al., 2012) on 1.5 x 1.2 m laminated glazing samples made up with two 3 mm glass layers and a central 1.52 mm PVB membrane, using a 15 and 30 kg charge masses (TNT equivalent) at 13-16 m stand-off. The fourth blast test (Test 4) was conducted on a larger 3.6 x 2.0 m pane of 13.52 mm thickness, using a 100 kg charge mass (TNT equivalent) at a 17 m stand-off. All blast tests employed the Digital Image Correlation (DIC) technique to obtain 3D out-of-plane deflections and strains. The proposed analytical method reproduced the experimental deflection profiles, with the best estimates obtained for the more severe loading cases. Reaction forces were also compared with experimental estimates. The predictive ability of the proposed method could permit more accurate designs to be produced rapidly, improving structures resistance to such loadings.

Journal article

Rolfe E, Arora H, Hooper PA, Dear JPet al., 2018, Hybrid composite sandwich panels under blast and impact loading, ISSN: 2101-6275

© 2018 The Authors, published by EDP Sciences. Naval vessels may undergo high strain rate loading, including impact, wave slamming and blast loading. Predicting the behaviour of composite sandwich structures to such loading is complicated, hence representative experiments are required. Two panels with hybrid carbon-and glass-fibre skins were fabricated and subjected to full-scale air blast loading. The panels were 1.7 × 1.5 m in size and were subjected to a 100 kg nitromethane charge at a stand-off distance of 15 m. 3D Digital Image Correlation (DIC) was implemented behind each of the panels to record the full-field out-of-plane displacement of the panels. In addition, the panels were instrumented with foil strain gauges on the front skins to record the response of the panel side in contact with the blast. The results revealed that the combination of glass-and carbon-fibre improves the blast resilience when compared to previous blast testing on panels with exclusively glass-fibre or carbon-fibre skins. However, the order in which the glass-and carbon-fibre layers were arranged did not have a significant effect on the overall panel performance. In addition, panels with the same hybrid skins were subjected to high velocity impact testing. An aluminium projectile with 25 mm diameter was fired at small scale panels (160 × 160 mm) using a laboratory gas gun at a velocity of 78 ms-1. 3D DIC was again used to record the out-of-plane displacement of these panels. In contrast to the blast experiment, the impact results showed that the order in which glass-and carbon-fibres were arranged did affect both the out-of-plane displacement and damage to the panels. The least damage occurred when glass-fibre layers were placed on the outermost layers impacted by the projectile.

Conference paper

Rolfe E, Quinn R, Sancho A, Kaboglu C, Johnson A, Liu H, Hooper PA, Dear JP, Arora Het al., 2018, Blast resilience of composite sandwich panels with hybrid glass-fibre and carbon-fibre skins, Multiscale and Multidisciplinary Modeling, Experiments and Design, Vol: 1, Pages: 197-210, ISSN: 2520-8160

The development of composite materials through hybridisation is receiving a lot of interest; due to the multiple benefits, this may bring to many industries. These benefits include decreased brittle behaviour, which is an inherent weakness for composite materials, and the enhancement of mechanical properties due to the hybrid effect, such as tensile and flexural strength. The effect of implementing hybrid composites as skins on composite sandwich panels is not well understood under high strain rate loading, including blast loading. This paper investigates the blast resilience of two types of hybrid composite sandwich panel against a full-scale explosive charge. Two hybrid composite sandwich panels were mounted at a 15 m stand-off distance from a 100 kg nitromethane charge. The samples were designed to reveal whether the fabric layup order of the skins influences blast response. Deflection of the sandwich panels was recorded using high-speed 3D digital image correlation (DIC) during the blast. It was concluded that the combination of glass-fibre reinforced polymer (GFRP) and carbon-fibre reinforced polymer (CFRP) layers in hybrid laminate skins of sandwich panels decreases the normalised deflection compared to both GFRP and CFRP panels by up to 41 and 23%, respectively. The position of the glass-fibre and carbon-fibre layers does not appear to affect the sandwich panel deflection and strain. A finite element model has successfully been developed to predict the elastic response of a hybrid panel under air blast loading. The difference between the maximum central displacement of the experimental data and numerical simulation was ca. 5% for the hybrid panel evaluated.

Journal article

Rolfe E, Kaboglu C, Quinn R, Hooper PA, Arora H, Dear JPet al., 2018, High velocity impact and blast loading of composite sandwich panels with novel carbon and glass construction, Journal of Dynamic Behavior of Materials, Vol: 4, Pages: 359-372, ISSN: 2199-7446

This research investigates whether the layup order of the carbon-fibre/glass-fibre skins in hybrid composite sandwich panels has an effect on impact response. Composite sandwich panels with carbon-fibre/glass-fibre hybrid skins were subjected to impact at velocities of 75 ± 3 and 90 ± 3 m s−1. Measurements of the sandwich panels were made using high-speed 3D digital image correlation (DIC), and post-impact damage was assessed by sectioning the sandwich panels. It was concluded that the introduction of glass-fibre layers into carbon-fibre laminate skins reduces brittle failure compared to a sandwich panel with carbon-fibre reinforced polymer skins alone. Furthermore, if the impact surface is known, it would be beneficial to select an asymmetrical panel such as Hybrid-(GCFGC) utilising glass-fibre layers in compression and carbon-fibre layers in tension. This hybrid sandwich panel achieves a specific deflection of 0.322 mm kg−1 m2 and specific strain of 0.077% kg−1 m2 under an impact velocity of 75 ± 3 m s−1. However, if the impact surface is not known, selection of a panel with a symmetric yet more dispersed hybridisation would be effective. By distributing the different fibre layers more evenly within the skin, less surface and core damage is achieved. The distributed hybrid investigated in this research, Hybrid-(GCGFGCG), achieved a specific deflection of 0.394 mm kg−1 m2 and specific strain of 0.085% kg−1 m2 under an impact velocity of 75 ± 3 m s−1. Blast loading was performed on a large scale version of Hybrid-(GCFGC) and it exhibited a maximum deflection of 75 mm following a similar deflection profile to those observed for the impact experiments.

Journal article

arora H, nila A, Vitharana K, sherwood JM, nguyen T-TN, Karunaratne A, Mohammed IK, bodey A, hellyer PJ, overby DR, schroter RC, hollis Det al., 2017, Microstructural consequences of blast lung injury characterised with digital volume correlation, Frontiers in Materials, Vol: 4, ISSN: 2296-8016

This study focuses on microstructural changes that occur within the mammalian lung when subject to blast and how these changes influence strain distributions within the tissue. Shock tube experiments were performed to generate the blast injured specimens (cadaveric Sprague-Dawley rats). Blast overpressures of 100 and 180 kPa were studied. Synchrotron tomography imaging was used to capture volumetric image data of lungs. Specimens were ventilated using a custom-built system to study multiple inflation pressures during each tomography scan. These data enabled the first digital volume correlation (DVC) measurements in lung tissue to be performed. Quantitative analysis was performed to describe the damaged architecture of the lung. No clear changes in the microstructure of the tissue morphology were observed due to controlled low- to moderate-level blast exposure. However, significant focal sites of injury were observed using DVC, which allowed the detection of bias and concentration in the patterns of strain level. Morphological analysis corroborated the findings, illustrating that the focal damage caused by a blast can give rise to diffuse influence across the tissue. It is important to characterize the non-instantly fatal doses of blast, given the transient nature of blast lung in the clinical setting. This research has highlighted the need for better understanding of focal injury and its zone of influence (alveolar interdependency and neighboring tissue burden as a result of focal injury). DVC techniques show great promise as a tool to advance this endeavor, providing a new perspective on lung mechanics after blast.

Journal article

Logan N, Arora H, Higgins C, 2017, Evaluating primary blast effects in vitro, Jove-Journal of Visualized Experiments, Vol: 127, ISSN: 1940-087X

Exposure to blast events can cause severe trauma to vital organs such as the lungs, ears, and brain. Understanding the mechanisms behind such blast-induced injuries is of great importance considering the recent trend towards the use of explosives in modern warfare and terrorist-related incidents. To fully understand blast-induced injury, we must first be able to replicate such blast events in a controlled environment using a reproducible method. In this technique using shock tube equipment, shock waves at a range of pressures can be propagated over live cells grown in 2D, and markers of cell viability can be immediately analyzed using a redox indicator assay and the fluorescent imaging of live and dead cells. This method demonstrated that increasing the peak blast overpressure to 127 kPa can stimulate a significant drop in cell viability when compared to untreated controls. Test samples are not limited to adherent cells, but can include cell suspensions, whole-body and tissue samples, through minor modifications to the shock tube setup. Replicating the exact conditions that tissues and cells experience when exposed to a genuine blast event is difficult. Techniques such as the one presented in this article can help to define damage thresholds and identify the transcriptional and epigenetic changes within cells that arise from shock wave exposure.

Journal article

Rolfe E, Kaboglu C, Kelly M, Arora H, Hooper PA, Dear JPet al., 2017, Evaluating the blast performance of sandwich structures with novel carbon and glass construction, 21 st International Conference on Composite Materials

© 2017 International Committee on Composite Materials. All rights reserved. The brittle nature of composite materials results in the overdesign of composite components which counteracts their benefits. Naval vessels undergo a spectrum of loading from static to dynamic due to wave slamming, impact and blast loads. Experiments investigating the performance of composite laminates and composite sandwich panels under static and dynamic conditions are the focus of the research presented in this paper. By hybridizing composites, researchers seek to improve their ductility. Interlaminar glass-/carbon-fiber hybrids are investigated in this study as they can be manufactured in large volumes at a reasonable cost. Three interlaminar hybrids along with a glass-fiber and a carbon-fiber laminate were manufactured and tested under quasi-static tension and flexure. In flexure, one hybrid had greater strain to failure than the purely glass-fiber laminate and another dissipated more energy than the glass-fiber laminate. All hybrids demonstrated greater strain to failure than the carbon-fiber laminate and greater flexural strength than either constituent materials. In tension, the elastic moduli and the tensile strength of the hybrids lay between that of the glass- and carbon-fiber laminates. Once again all hybrids had greater strain to failure in tension than the carbon-fiber laminates, however, none exceeded the glass-fiber laminates. Composite sandwich panels with glass-fiber, carbon-fiber and hybrid laminate skins were subjected to impact testing using a gas gun and aluminium projectile. The carbon-fiber skins demonstrated brittle failure. The addition of glass-fiber layers into carbon-fiber skins improves their impact resilience and the stacking sequence of the fibers has an effect on panel deflection and rear skin strain.

Conference paper

Rolfe E, Kelly M, Arora H, Hooper PA, Dear JPet al., 2017, Failure analysis using X-ray computed tomography of composite sandwich panels subjected to full-scale blast loading, Composites Part B: Engineering, Vol: 129, Pages: 26-40, ISSN: 1359-8368

The tailorable mechanical properties and high strength-to-weight ratios of composite sandwich panels make them of interest to the commercial marine and naval sector, however, further investigation into their blast resilience is required. The experiments performed in this study aimed to identify whether alterations to the composite skins or core of a sandwich panel can yield improved blast resilience both in air and underwater. Underwater blast loads using 1.28 kg TNT equivalent charge at a stand-off distance of 1 m were performed on four different composite sandwich panels. Results revealed that implementing a stepwise graded density foam core, with increasing density away from the blast, reduces the deflection of the panel and damage sustained. Furthermore, the skin material affects the extent of panel deflection and damage, the lower strain to failure of carbon-fibre reinforced polymer (CFRP) skins reduces deflection but increases skin debonding. A further two panels were subjected to a 100 kg TNT air blast loading at a 15 m stand-off to compare the effect of a graded density core and the results support the underwater blast results. Future modelling of these experiments will aid the design process and should aim to include material damage mechanisms to identify the most suitable skins.

Journal article

Arora H, Rolfe E, Kelly M, Dear JPet al., 2017, Full-Scale Air and Underwater-Blast Loading of Composite Sandwich Panels, Explosion Blast Response of Composites, Pages: 161-199, ISBN: 9780081020920

© 2017 Elsevier Ltd. All rights reserved. This chapter reviews blast loading experiments performed on glass-fiber reinforced polymer (GFRP) and carbon-fiber reinforced polymer (CFRP) sandwich composite materials. The sandwich configurations employed both continuous and stepwise graded density core materials. Explosive charges of 1.28-100. kg trinitrotoluene (TNT) equivalent were used during these air and underwater-blast tests. The improved performance of composite sandwich structures with CFRP skins compared to GFRP equivalent constructions is demonstrated for air-blast experiments. In addition, there are benefits in terms of reduced deformation and back-skin integrity when employing graded density core materials. The benefits with regard to stiffer skin materials as well as the merits of graded cores have been identified during these studies. Mechanisms of failure have been established such as core crushing, skin/core cracking, delamination, and fiber breakage. Strain gauge data supported the mechanisms for such damage. A transition in behavior was observed in the sandwich panels when subject to a focused relatively near-field underwater blast as opposed to a far-field air-blast loading. Damage mechanisms notably shifted from distributed core shear failure originating from regions of high shear in air blast toward significant global core crushing (as well as cracking) in underwater blast. The full-scale experimental results presented here will assist in the development of analytical and computational models.

Book chapter

Rolfe E, Kelly M, Arora H, Dear JPet al., 2017, Composite materials for blast applications in air and underwater, Dynamic Response and Failure of Composite Materials and Structures, Pages: 263-295, ISBN: 9780081008874

© 2017 Elsevier Ltd All rights reserved. Due to the attractive properties of polymeric sandwich composites, including low-density and low-radar signatures, these materials are becoming increasingly commonplace in the naval industry. This chapter details the performance of glass-fiber and carbon-fiber reinforced polymer sandwich composites subjected to air and underwater blast loading. A range of polymeric foam cores was assessed along with a novel graded core. Explosive charges of 1.28-100. kg TNT equivalent were used during the experiments. The response and damage inflicted by the blast loading was assessed from surface strain measurements, using digital image correlation and strain gauges, and postblast specimen analysis using X-ray computed tomography (CT) scanning. This chapter describes the experimental designs and highlights the damage and degradation characteristics of sandwich composites subjected to blast loading.

Book chapter

Arora H, Del Linz P, Dear J, 2017, Damage and deformation in composite sandwich panels exposed to multiple and single explosive blasts, International Journal of Impact Engineering, Vol: 104, Pages: 95-106, ISSN: 0734-743X

The blast resistance of glass- bre reinforced polymer (GFRP) sandwich struc-tures has been investigated for increasing shock intensity and for multipleblast exposures. In this study, sandwich panels of 1.6 m x 1.3 m were subjec-ted to 30 kg charges of C4 explosive at stand-o distances from 8 m to 16 m.These targets formed part of two studies presented here: one, to observe theloading of the same geometry of target to an increasing shock intensity; andthe second, to observe the response of one target to multiple blast impacts.Experimental data provides detailed data for sandwich panel response,which are often used in civil and military structures, where air-blast load-ing represents a serious threat. High-speed photography, with digital imagecorrelation (DIC), and laser gauge systems were employed to monitor thedeformation of these structures during the blasts. The experimental dataprovides for the development of analytical and computational models. Ini-tial analysis of the blast experiments are presented alongside a nite elementmodel to establish trends in deformation behaviour. Details of failure mech-anisms and the conditions for the onset of failure are also discussed.

Journal article

Dear JP, Rolfe E, Kelly M, Arora H, Hooper PAet al., 2017, Blast performance of composite sandwich structures, 11th International Symposium on Plasticity and Impact Mechanics (IMPLAST), Publisher: Elsevier, Pages: 471-478, ISSN: 1877-7058

A range of composite sandwich panels with different polymeric foam cores and face-sheets were subjected to full-scale air and underwater blast testing. The air blast panels had glass fiber reinforced polymer (GFRP) face-sheets with three different polymeric foam cores: styrene acrylonitrile (SAN), polyvinylchloride (PVC) and polymethacrylimide (PMI). The panels were subjected to 100 kg TNT equivalent charge from a stand-off of 15 m. The SAN panel had the lowest deflection and suffered from the least damage. The underwater blast panels had either a single density or graded density SAN foam core and either glass fiber reinforced polymer or carbon fiber reinforced polymer (CFRP) face-sheets. The research revealed that there is a trade-off between reduced panel deflection and damage. All the blast research that has been performed is part of a program sponsored by the Office of Naval Research (ONR).

Conference paper

Arora H, Del Linz P, Dear JP, Damage and deformation in composite sandwich panels exposed to multiple and single explosive blasts, International Journal of Impact Engineering, ISSN: 1879-3509

Journal article

Rolfe E, Kelly M, Arora H, Hooper PA, Dear JPet al., 2016, X-ray CT analysis after blast of composite sandwich panels, Procedia Engineering, Vol: 167, Pages: 176-181, ISSN: 1877-7058

Four composite sandwich panels with either single density or graded density foam cores and different face-sheet materials were subjected to full-scale underwater blast testing. The panels were subjected to 1kg PE4 charge at a stand-off distance of 1 m. The panel with graded density core and carbon fiber face-sheets had the lowest deflection. Post-blast damage assessment was carried out using X-ray CT scanning. The damage assessment revealed that there is a trade-off between reduced panel deflection and panel damage. This research has been performed as part of a program sponsored by the Office of Naval Research (ONR).

Journal article

Andrikakou P, Vickraman K, Arora H, 2016, On the behaviour of lung tissue under tension and compression, Scientific Reports, Vol: 6, ISSN: 2045-2322

Lung injuries are common among those who suffer an impact or trauma. The relative severity of injuries up to physical tearing of tissue have been documented in clinical studies. However, the specific details of energy required to cause visible damage to the lung parenchyma are lacking. Furthermore, the limitations of lung tissue under simple mechanical loading are also not well documented. This study aimed to collect mechanical test data from freshly excised lung, obtained from both Sprague-Dawley rats and New Zealand White rabbits. Compression and tension tests were conducted at three different strain rates: 0.25, 2.5 and 25 min−1. This study aimed to characterise the quasi-static behaviour of the bulk tissue prior to extending to higher rates. A nonlinear viscoelastic analytical model was applied to the data to describe their behaviour. Results exhibited asymmetry in terms of differences between tension and compression. The rabbit tissue also appeared to exhibit stronger viscous behaviour than the rat tissue. As a narrow strain rate band is explored here, no conclusions are being drawn currently regarding the rate sensitivity of rat tissue. However, this study does highlight both the clear differences between the two tissue types and the important role that composition and microstructure can play in mechanical response.

Journal article

Del Linz P, Wang Y, Hooper PA, Arora H, Smith D, Pascoe L, Cormie D, Blackman BRK, Dear JPet al., 2016, Determining Material Response for Polyvinyl Butyral (PVB) in Blast Loading Situations, Experimental Mechanics, Vol: 56, Pages: 1501-1517, ISSN: 1741-2765

Protecting structures from the effect of blast loads requires the careful design of all building components. In this context, the mechanical properties of Polyvinyl Butyral (PVB) are of interest to designers as the membrane behaviour will affect the performance of laminated glass glazing when loaded by explosion pressure waves. This polymer behaves in a complex manner and is difficult to model over the wide range of strain rates relevant to blast analysis. In this study, data from experimental tests conducted at strain rates from 0.01 s−1 to 400 s−1 were used to develop material models accounting for the rate dependency of the material. Firstly, two models were derived assuming Prony series formulations. A reduced polynomial spring and a spring derived from the model proposed by Hoo Fatt and Ouyang were used. Two fits were produced for each of these models, one for low rate cases, up to 8 s−1, and one for high rate cases, from 20 s−1. Afterwards, a single model representing all rates was produced using a finite deformation viscoelastic model. This assumed two hyperelastic springs in parallel, one of which was in series with a non-linear damper. The results were compared with the experimental results, assessing the quality of the fits in the strain range of interest for blast loading situations. This should provide designers with the information to choose between the available models depending on their design needs.

Journal article

Barnett-Vanes A, Sharrock A, Eftaxiopoulou T, Arora H, Macdonald W, Bull AM, Rankin SMet al., 2016, CD43Lo classical monocytes participate in the cellular immune response to isolated primary blast lung injury, Journal of Trauma and Acute Care Surgery, Vol: 81, Pages: 500-511, ISSN: 2163-0763

BACKGROUND: Understanding of the cellular immune response to primary blast lung injury (PBLI) is limited, with only the neutrophil response well documented. Moreover, its impact on the immune response in distal organs remains poorly understood. In this study, a rodent model of isolated primary blast injury was used to investigate the acute cellular immune response to isolated PBLI in the circulation and lung; including the monocyte response, and investigate distal sub-acute immune effects in the spleen and liver 6hr after injury. METHODS: Rats were subjected to a shock wave (~135kPa overpressure, 2ms duration) inducing PBLI or sham procedure. Rat physiology was monitored and at 1, 3 and 6 hr thereafter blood, lung, and Broncho-alveolar lavage fluid (BALF) were collected and analysed by flow cytometry (FCM), ELISA and Histology. In addition, at 6hr spleen and liver were collected and analysed by FCM. RESULTS: Lung histology confirmed pulmonary barotrauma and inflammation. This was associated with rises in CXCL-1, IL-6, TNF-α and albumin protein in the BALF. Significant acute increases in blood and lung neutrophils and CD43Lo/His48Hi (classical) monocytes/macrophages were detected. No significant changes were seen in blood or lung 'non-classical' monocyte, NK, B or T Cells. In the BALF, significant increases were seen in neutrophils, CD43Lo monocyte-macrophages and MCP-1. Significant increases in CD43Lo and Hi monocyte-macrophages were detected in the spleen at 6hr. CONCLUSIONS: This study reveals a robust and selective response of CD43Lo/His48Hi (classical) monocytes - in addition to neutrophils - in blood and lung tissue following PBLI. An increase in monocyte-macrophages was also observed in the spleen at 6hr. This profile of immune cells in the blood and BALF could present a new research tool for translational studies seeking to monitor, assess or attenuate the immune response in blast injured patients. EVIDENCE: Experimental laboratory study.WC- 300.

Journal article

Del Linz P, Hooper PA, Arora H, Wang Y, Smith D, Blackman BRK, Dear JPet al., 2016, Delamination properties of laminated glass windows subject to blast loading, International Journal of Impact Engineering, Vol: 105, Pages: 39-53, ISSN: 1879-3509

Delamination processes absorb significant amounts of energy in laminated glass windows when they are subjected to blast loads. Blast tests were performed previously and their results had been used to calculate the loads imposed on the support systems. In this research, the delamination process at realistic deformation rates was studied to understand the reaction force response obtained. Laboratory tensile tests were performed on pre-cracked laminated glass specimens to investigate their delamination behaviour. The experiments confirmed the presence of a plateau in the force-deflection graphs, suggesting that the delamination process absorbed significant energy. The experimental results were then employed to calibrate FEA models of the delamination process with the aim of estimating the delamination energy of the polyvinyl butyral (PVB) membrane and glass layers and its relationship with deformation speed. The delamination energies obtained through this research, if used with the appropriate PVB material model, are a valuable new tool new tool in the modelling and design of laminated glass façade structures.

Journal article

Arora H, Eftaxiopoulou T, 2016, Physical models: Organ Models for Primary Blast, Blast Injury Science and Engineering A Guide for Clinicians and Researchers, Publisher: Springer, ISBN: 9783319218670

This book aims to help clinicians who seek to conduct science and engineering based research on blast injuries as well as engineers and scientists who seek to apply their expertise to address blast injuries. Blast injuries are prevalent.

Book chapter

Eftaxiopoulou T, Barnett-Vanes A, Arora H, Macdonald W, Nguyen TTN, Itadani M, Sharrock AE, Britzman D, Proud WG, Bull AMJ, Rankin SMet al., 2016, Prolonged but not short duration blast waves elicit acute inflammation in a rodent model of primary blast limb trauma, Injury, Vol: 47, Pages: 625-632, ISSN: 0020-1383

BackgroundBlast injuries from conventional and improvised explosive devices account for 75% of injuries from current conflicts; of these over 70% involve the limbs. Variable duration and magnitude of blast wave loading occurs in real-life explosions and is hypothesised to cause different injuries. While a number of in-vivo models report the inflammatory response to blast injuries, the extent of this response has not been investigated with respect to the duration of the primary blast wave. The relevance is that explosions in open air are of short duration compared to those in confined spaces. MethodsHind limbs of adult Sprauge-Dawley rats were subjected to focal isolated primary blast waves of varying overpressure (1.8-3.65kPa) and duration (3.0-11.5ms), utilising a shock tube and purpose built experimental rig. Rats were monitored during and after blast. At 6 and 24hrs after exposure blood, lungs, liver and muscle tissue were collected and prepared for histology and flow cytometry.ResultsAt 6hrs increases in circulating neutrophils and CD43Lo/His48Hi monocytes were observed in rats subjected to longer duration blast waves. This was accompanied by increases in circulating pro-inflammatory chemo/cytokines KC and IL-6. No changes were observed with shorter duration blast waves irrespective of overpressure. In all cases, no histological damage was observed in muscle, lung or liver. By 24hrs post-blast all inflammatory parameters had normalised. ConclusionsWe report the development of a rodent model of primary blast limb trauma that is the first to highlight an important role played by blast wave duration and magnitude in initiating acute inflammatory response following limb injury in the absence of limb fracture or penetrating trauma. The combined biological and mechanical method developed can be used to further understand the complex effects of blast waves in a range of different tissues and organs in-vivo.

Journal article

Del Linz P, Hooper PA, Arora H, Smith D, Pascoe L, Cormie D, Blackman BRK, Dear JPet al., 2015, Reaction forces of laminated glass windows subject to blast loads, Composite Structures, Vol: 131, Pages: 193-206, ISSN: 1879-1085

Several blast trials on laminated glass windows have been performed in the past, using both full field 3D Digital Image Correlation and strain gauges located on the supporting structure to collect information on the glass pane behaviour. The data obtained during three blast experiments were employed to calculate reaction forces throughout the perimeter supports both before and after the fracture of the glass layers. The pre-crack experimental data were combined with finite element modelling results to achieve this, whilst solely experimental results were employed for post-cracked reactions. The results for the three blast experiments were compared to identify similarities in their behaviour. It is intended that the results can be used to improve the existing spring–mass systems used for the design of blast resistant windows.

Journal article

Arora H, Tarleton E, Li-Mayer J, Charalambides M, Lewis Det al., 2015, Modelling the damage and deformation process in a plastic bonded explosive microstructure under tension using the finite element method, Computational Materials Science, Vol: 110, Pages: 91-101, ISSN: 0927-0256

Modelling the deformation and failure processes occurring in polymer bonded explosives (PBX)and other energetic materials is of great importance for processing methods and lifetime storagepurposes. Crystal debonding is undesirable since this can lead to contamination and a reductionin mechanical properties. An insensitive high explosive (PBX-1) was the focus of the study.This binary particulate composite consists of (TATB) filler particles encapsulated in a polymericbinder (KELF800). The particle/matrix interface was characterised with a bi-linear cohesive law,the filler was treated as elastic and the matrix as visco-hyperelastic. Material parameters weredetermined experimentally for the binder and the cohesive parameters were obtained previouslyfrom Williamson et al. (2014) and Gee et al. (2007) for the interface. Once calibrated, the materiallaws were implemented in a finite element model to allow the macroscopic response of thecomposite to be simulated. A finite element mesh was generated using a SEM image to identifythe filler particles which are represented as a set of 2D polygons. Simulated microstructureswere also generated with the same size distribution and volume fraction only with the idealisedassumption that the particles are a set of circles in 2D and spheres in 3D. The various modelresults were compared and a number of other variables were examined for their influence on theglobal deformation behaviour such as strain rate, cohesive parameters and contrast between fillerand matrix modulus. The overwhelming outcome is that the geometry of the particles plays acrucial role in determining the onset of failure and the severity of fracture in relation to whetherit is a purely local or global failure. The model was validated against a set of uniaxial tensiletests on PBX-1 and it was found that it predicted the initial modulus and failure stress and strainwell.Keywords: Particulate composites, High volume fraction, Finite Element Analysis,Micromechanics, Fract

Journal article

Kelly M, Arora H, Worley A, Kaye M, Del Linz P, Hooper PA, Dear JPet al., 2015, Sandwich panel cores for blast applications: materials and graded density, Experimental Mechanics, Vol: 56, ISSN: 1741-2765

Sandwich composites are of interest in marine applications dueto their high strength-to-weight ratio and tailorable mechanical properties, but their resistance to air blast loading is not well understood. Full-scale 100 kg TNT equivalent air blast testing at a 15 m stand-off distance wasperformed on glass-fibre reinforced polymer (GFRP) sandwich panels withpolyvinyl chloride (PVC); polymethacrylimid (PMI); and styrene acrylonitrile(SAN) foam cores, all possessing the same thickness and density. Further testingwas performed to assess the blast resistance of a sandwich panel containinga stepwise graded density SAN foam core, increasing in density away from theblast facing side. Finally a sandwich panel containing compliant polypropylene(PP) fibres within the GFRP front face-sheet, was subjected to blast loadingwith the intention of preventing front face-sheet cracking during blast. Measurementsof the sandwich panel responses were made using high-speed digital image correlation (DIC), and post-blast damage was assessed by sectioning thesandwich panels and mapping the damage observed. It was concluded that allcores are effective in improving blast tolerance and that the SAN core wasthe most blast tolerant out of the three foam polymer types, with the DIC resultsshowing a lower deflection measured during blast, and post-blast visualinspections showing less damage suffered. By grading the density of the core itwas found that through thickness crack propagation was mitigated, as well asdamage in the higher density foam layers, thus resulting in a smoother backface-sheet deflection profile. By incorporating compliant PP fibres into thefront face-sheet, cracking was prevented in the GFRP, despite damage beingpresent in the core and the interfaces between the core and face-sheets.

Journal article

Butler BJ, Bo C, Boddy RL, Arora H, Williams A, Proud WG, Brown KAet al., 2015, Composite nature of fresh skin revealed during compression, Bioinspired, Biomimetic and Nanobiomaterials, Vol: 4, Pages: 133-139, ISSN: 2045-9858

Journal article

Kelly M, Arora H, Dear JP, 2015, Blast resistance of polymeric composite sandwich Structures, Structural Integrity and Durability of Advanced Composites Innovative Modelling Methods and Intelligent Design, Publisher: Woodhead Publishing, ISBN: 9780081001387

This comprehensive text provides the information users need to understand deformation and fracture phenomena resulting from impact, fatigue, creep, and stress corrosion cracking and how these phenomena can affect reliability, life ...

Book chapter

Arora H, Kelly M, Worley A, Del Linz P, Fergusson A, Hooper PA, Dear JPet al., 2015, Compressive strength after blast of sandwich composite materials., Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 372, ISSN: 1471-2962

Composite sandwich materials have yet to be widely adopted in the construction of naval vessels despite their excellent strength-to-weight ratio and low radar return. One barrier to their wider use is our limited understanding of their performance when subjected to air blast. This paper focuses on this problem and specifically the strength remaining after damage caused during an explosion. Carbon-fibre-reinforced polymer (CFRP) composite skins on a styrene-acrylonitrile (SAN) polymer closed-cell foam core are the primary composite system evaluated. Glass-fibre-reinforced polymer (GFRP) composite skins were also included for comparison in a comparable sandwich configuration. Full-scale blast experiments were conducted, where 1.6×1.3 m sized panels were subjected to blast of a Hopkinson-Cranz scaled distance of 3.02 m kg(-1/3), 100 kg TNT equivalent at a stand-off distance of 14 m. This explosive blast represents a surface blast threat, where the shockwave propagates in air towards the naval vessel. Hopkinson was the first to investigate the characteristics of this explosive air-blast pulse (Hopkinson 1948 Proc. R. Soc. Lond. A 89, 411-413 (doi:10.1098/rspa.1914.0008)). Further analysis is provided on the performance of the CFRP sandwich panel relative to the GFRP sandwich panel when subjected to blast loading through use of high-speed speckle strain mapping. After the blast events, the residual compressive load-bearing capacity is investigated experimentally, using appropriate loading conditions that an in-service vessel may have to sustain. Residual strength testing is well established for post-impact ballistic assessment, but there has been less research performed on the residual strength of sandwich composites after blast.

Journal article

Kelly M, Arora H, Worley A, Linz PD, Fergusson A, Hooper PA, Hayman B, Dear JPet al., 2015, Blast performance of composite sandwich structures

© 2015 International Committee on Composite Materials. All rights reserved. Sandwich composite materials possess low radar signatures, high strength-to-weight ratios and tailorable mechanical properties, but their blast resistance is not well understood. This paper presents the results of full scale air blast tests performed on a graded density foam core sandwich panel, to determine if the use of a graded core can be used to mitigate blast damage. The results are obtained using high speed 3D digital image correlation, and post-blast damage assessment. It was found that back face-sheet damage could be prevented by using a graded sandwich panel as there is less cracking towards the back of the panel, and the epoxy between the foam layers impedes crack propagation through the foam, resulting in less overall damage. The second part of this paper presents findings from a study performed using the UNDEX simulation tool in Abaqus to model the fluid-structure-interaction in underwater blast scenarios. These results were verified with full scale underwater blast testing performed in Norway in 1988 in connection with the development of a series of mine countermeasure vessels for the Royal Norwegian Navy. Using this method it was possible to successfully model cavitation development and closure in front of the tested sandwich structure, and strong agreement was found from electrical strain gauges placed on the front face-sheet of the sandwich panels in the underwater blast test experiments.

Conference paper

Kelly M, Arora H, Dear JP, 2014, The comparison of various foam polymer types in composite sandwich panels subjected to full scale air blast loading, Procedia Engineering, Vol: 88, Pages: 48-53, ISSN: 1877-7058

Full scale air blast testing has been performed on a range of polymeric foam composite panels. These panels employed glass fibre reinforced polymer (GFRP) face-sheets with different polymer foam cores, namely: Styrene acrylonitrile (SAN); Polyvinylchloride (PVC) and Polymethacrylimide (PMI). The three sandwich panels were all subjected to 100 kg TNT equivalent blast loading at a stand-off distance of 15 m, and the responses of the panels were measured using Digital Image Correlation (DIC). The extent of damage in the sandwich panels was then inspected via post-blast sectioning, and it was found that the SAN core suffered the least damage, and the PMI suffered the most. The DIC showed that the deflection of the SAN core sandwich panel was much less than the other two foam polymer cores, due to less damage meaning a greater stiffness was retained. All blast research to date is part of a programme sponsored by the Office of Naval Research (ONR).

Journal article

Arora H, Charalambides MN, Tarleton E, Williamson DM, Leppard CLet al., 2013, An image based approach to modelling plastic bonded explosives (PBX) on the micro scale, Pages: 5391-5397

Conference paper

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