Evaluation of blast protection using novel-shaped water-filled containers: experiments and simulations

A combined experimental and numerical investigation was conducted into evaluating the influence of the geometry of a water-filled container on maximising the reduction in deformation it provides to a high-strength steel plate subject to localised blast loading. Experiments were conducted with a range of novel container shapes including a cone, inverted cone, diamond and mushroom. In addition to these container shapes, an array of water bottles known as a kinetic energy defeat device (KEDD) and a high performing quadrangular container design were also evaluated. The performance of each container was evaluated in terms of both the reduction in deformation of a steel target plate and the efficiency of the mitigation in terms of the reduction per unit mass of water. The numerical simulations were found to provide adequate predictions for the novel container shapes. They were then used to isolate the differences in target loading for each container type. Further numerical simulations were then performed to identify improvements in the design of the best performing containers. The best performing novel geometries were the mushroom and inverted cone shaped containers, which are more effective at radially spreading the water. However, the mushroom shaped container was the only container found to outperform the most efficient quadrangular container on a mass efficiency basis. The results of this investigation can be used to assist in the design of water-filled containers that are used as part of a near-field blast protection system on an armoured vehicle or other protected structure

Wear of some commercial epoxy resin/ceramic particle composites by sliding and impact abrasion

This paper presents measurements of the wear rates and an examination of the wear mechanisms of some commercially available epoxy resins filled with ceramic particles when subjected to either sliding abrasion or impact abrasion. The sliding and impact wear tests were performed using a pin-on-drum machine and a paddle test abrasion machine, respectively. When the specimens were abraded against either glass, garnet or silicon carbide paper in the sliding wear tests it was found that ceramic particles improve the wear resistance of epoxy resins. Large sintered ceramic granules appear more effective in resisting sliding abrasion than small ceramic particles. During impact abrasion, however, the ceramic particles either cause a slight reduction or do not affect the wear resistance of epoxy resins. In both sliding abrasion and impact abrasion the epoxy resin in the composites was worn by the processes of microploughing, microcutting and microcracking. The ceramic particles were worn by fracture, chipping and pull-out, however the severity of fracture and chipping was higher in impact abrasion than in sliding abrasion

Blast mitigation with fluid containers: effect of mitigant type

The effect of filled external containers on the deformation induced in a steel plate under near-field blast loading has been investigated through a combined numerical and experimental study. Six different fill materials (mitigants) were considered for inducing near-field blast mitigation. The mitigants evaluated were bulk water, aerated water, sand, expanded polystyrene (EPS), a combination of EPS and water, and shear thickening fluid. The performance of the mitigants depended on their mass, with sand providing the best mitigation and EPS the worst for a given volume. Bulk water provided the greatest reduction of the peak deformation per unit of added mass. The mitigant material also had a significant effect on the deformation-time history of the steel plate. The sand and ½ EPS + ½ water containers were found to significantly delay the arrival of the pressure wave at the target surface due to their compressibility and low sound speed. Numerical analysis reveals that different mechanisms induce blast mitigation, and these are identified for each of the different mitigant materials

Prediction of mode I delamination resistance of z-pinned laminates using the embedded finite element technique

A new finite modelling approach is presented to analyse the mode I delamination fracture toughness of z-pinned laminates using the computationally efficient embedded element technique. In the FE model, each z-pin is represented by a single one-dimensional truss element that is embedded within the laminate. Each truss is given the material, geometric and spatial properties associated with the global crack bridging traction response of a z-pin in the laminate; this simplification provides a computationally efficient and flexible model where pin elements are independent of the underlying structural mesh for the laminate. The accuracy of the FE modelling approach is assessed using mode I interlaminar fracture toughness data for a carbon-epoxy laminate reinforced with z-pins made of copper, titanium or stainless steel. The model is able to predict with good accuracy the crack growth resistance curves and fracture toughness properties for the different types of z-pinned laminate

Vibration based structural health monitoring of adhesively bonded composite scarf repairs

Structural health monitoring (SHM) may be applied to bonded composite repairs to enable the continuous through-life assessment of structural integrity. Further, adhesively bonded joints are an ideal starting point for real-time, in-situ monitoring due to knowledge of mechanisms and locations of failure. The development of a SHM technique for the detection of debonding in scarf and overply repairs based on the frequency response of the repaired structure is described in this paper. Experimental investigations were conducted on representative carbon / epoxy composite scarf and overply joints. Piezoelectric elements were used to excite and measure the response of the repaired structure. The frequency response signature of the repaired structure with simulated debonds was found to differ significantly from that of the undamaged repair for two sets of boundary conditions. This demonstrates the potential of this technique for the SHM of scarf repaired composite structures

Synergistic delamination toughening of composites using multi-scale carbon reinforcements

Multi-scale toughening is a key strategy employed by biological systems, made of intrinsically brittle constituents, to achieve high damage tolerance. This paper presents an investigation of the synergistic enhancements to the mode I interlaminar fracture toughness of fibre-polymer composite laminates using multi-scale carbon reinforcements. By combining carbon nanofibres (CNFs) dispersed in the matrix and z-pins in the laminate thickness at various contents, an extra mechanism of energy dissipation occurs. This additional mechanism synergistically improves the laminate's resistance to delamination growth under mode I loading. Addition of the nanofibres in the matrix increases the interfacial strength and frictional energy dissipation during z-pin pull-out, thus generating a greater-than-additive toughening effect that would not have existed should either the nanofibres or the z-pins been deployed alone. The results reveal that the magnitude of the synergistic toughening effect was dependent on the volume fraction and combinations of CNFs and z-pins used; where synergy values ranged between 24 and 69% over the expected additive toughness value. A numerical model was developed to successfully predict the crack growth resistance and the synergistic toughening effect with filler content of the multi-scale composites