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Pearce G.M.K.,University of New South Wales | Johnson A.F.,German Aerospace Center | Hellier A.K.,University of New South Wales | Thomson R.S.,Cooperative Research Center for Advanced Composite Structures | Thomson R.S.,Advanced Composite Structures Australia Pty Ltd
Composite Structures

Pull-through failure of bolted joints in composites is due to the relatively low through-thickness properties of laminated materials. Recently it has been identified that pull-through failure also plays an important role in the ultimate bearing load and total energy absorption of bolted joints, especially under dynamic conditions. It has been previously found that bolted joints loaded in bearing exhibit rate sensitivity whereas bolts loaded in pull-through experience very little sensitivity, for nearly identical joint configurations. The primary focus of this paper was to use explicit finite element simulation of pull-through failure to shed light on discrepancies between experimentally observed rate sensitivity for seemingly similar tests. The paper uses the stacked-shell modelling approach to efficiently model the interaction of delamination and ply failure under the complex dynamic load state. The results of the simulation indicated that the properties of the interface susceptible to loading rate sensitivity, Mode I and II strain energy release rates (SERRs), did not have a great effect on the overall joint response; despite the prevalence of delamination during the failure process. A weak relationship between Mode II SERR and joint response was discovered which was consistent with experimental observations. © 2014 Elsevier Ltd. Source

Kepple J.,University of New South Wales | Kepple J.,Cooperative Research Center for Advanced Composite Structures | Herath M.T.,University of New South Wales | Pearce G.,University of New South Wales | And 4 more authors.
Composite Structures

The important role of imperfections on decreasing the buckling load of structural cylinders has been investigated by scientists and engineers for the past century, yet there is currently no method that is able to stochastically replicate the full range of realistic imperfections for a full account of possible buckling loads. This drawback impairs optimised design as designers are restrained to using an outdated and conservative design philosophy which dates from 1968. Modern manufacturing methods and materials such as composites require new, optimised design measures to take full advantage of their efficiencies. Stochastic analyses can optimise and improve the reliability of such cylinders through accurate prediction of the range of conceivable buckling loads by realistic simulation and sensitivity analyses. A stochastic procedure which realistically models imperfection sensitive composite shells is investigated in this paper. Monte-Carlo simulations of axially compressed cylinders with the full range of imperfection types are performed to show that the stochastic methods described here are able to accurately capture the scatter in the buckling load introduced from the imperfections. The results from a sensitivity analysis indicate that loading imperfections play the largest role in reducing the buckling load knockdown factors of the shell. © 2015 Elsevier Ltd. Source

Hou T.,University of New South Wales | Pearce G.M.K.,University of New South Wales | Prusty B.G.,University of New South Wales | Kelly D.W.,University of New South Wales | And 2 more authors.
Composite Structures

An experimental evaluation of the crushing behaviour of pressurised composite tubes is presented, with the intent to develop a variable load energy absorbing system. The influence of plug triggering radius on the energy absorption characteristics was determined. Seven different trigger radii were tested from 0. mm (sharp corner) to 6. mm. Experiments were performed under quasi-static (5. mm/min) and low speed (900. mm/min) conditions. It was found that there was a strong negative, yet nonlinear, correlation between the plug radius and the steady state crushing force of the tubes. The overall energy absorption of the composite tube specimens tested at higher crushing speed was slightly higher than those specimens tested at a lower rate.Internal pressurisation is presented as a method to vary the crushing force of the tubes. A novel sealing-crushing system was demonstrated to achieve a simultaneously crushing and pressurised tube. The tubes were then axially crushed at two internal pressure levels: 9 bar and 18 bar. It was found that the force due to internal pressure did contribute to the crushing force of the tubes and was a significant proportion of the unpressurised crush force (up to 60% in one case). The potential for an adaptable composite crushing element under a range of impact energy scenarios was also demonstrated for the development of a proposed variable load energy absorber for realistic crash conditions. © 2014 Elsevier Ltd. Source

Aggromito D.,Monash University | Aggromito D.,Cooperative Research Center for Advanced Composite Structures | Chen B.,Monash University | Thomson R.,Cooperative Research Center for Advanced Composite Structures | And 3 more authors.
International Journal of Industrial Ergonomics

Helicopter seats are designed to a specified mass range including equipment and can only provide limited energy absorbing protection within its designed energy absorbing capability. Over recent years, military occupants have been required to carry increasing amounts of equipment, which may affect the probability of injury during a crash. To investigate the effects of increasing equipment mass during a helicopter crash on injury, a linear 7-degree-of-freedom mass-spring-damper model is developed to simulate an occupant wearing body-borne equipment on a crashworthy helicopter seat. A fixed load energy absorption mechanism is also included in the model. To examine the effects of equipment attachment types, the mass bodies representing the equipment are attached with a spring and damper, with low and high stiffness values indicating loose and tight attachment respectively. Dimensional analysis shows that the maximum forces are proportional to the initial impact velocity prior to stroke. The results demonstrate that increasing the equipment mass reduces the seat's capability to absorb the total impact energy at higher initial impact velocities. The safe velocity, the velocity that prevents bottoming out, reduces from 10.2m/s, for an occupant without equipment, to 7.4m/s for an occupant with an equipment mass of 40kg at the lower and upper torso and 2kg at the head. When the equipment mass is 40kg at the hip and at the upper torso and 2kg at the head, a maximum increase on the underside of the pelvis of 173% is measured, providing an increased possibility of injury in the lumbar region. Increases of 321%, 889% and 335% on the maximum forces on the hip, upper torso and head respectively create the potential for contact injury at the hip, upper torso and head from equipment and more than a 50% chance of spinal injury. The results show that increasing equipment mass significantly increases the potential for injury at the lumbar, hip, upper torso and head. Relevance to industry: Relevance to industry: Military pilots today are required to wear a vast amount of equipment, that exceeds the weight limit of crashworthy helicopter seats. This paper demonstrates the disastrous effects of wearing large amounts whilst seated on a crashworthy helicopter seat in a simulated helicopter crash. © 2014 Elsevier B.V. Source

Djukic L.P.,Advanced Composite Structures Australia Pty Ltd | Leong A.Y.L.,Petronas | Falzon P.J.,Advanced Composite Structures Australia Pty Ltd | Leong K.H.,Petronas
Journal of Reinforced Plastics and Composites

A new glass/epoxy prepreg system has been developed as a solution to a long-standing challenge of corrosion and other damage, such as gouging and denting, sustained by piping, pipelines, and risers. The system has been designed to be applicable in the majority of operational conditions encountered in the oil and gas sector, encompassing onshore as well as offshore environments. This paper discusses the comprehensive qualification process undertaken to enable the repair of wall-thinning defects (Type A) and through-wall defects (Type B). The results show that the composite system meets the requirements of ISO/TS 24817 and so also concurrently complies with ASME PCC-2. © 2014 The Author(s). Source

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