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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 | Year: 2015

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 This drawback impairs optimised design as designers are restrained to using an outdated and conservative design philosophy which dates from 1968.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.


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 | Year: 2014

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.


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 | Year: 2014

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.


Baker A.,Advanced Composite Structures Australia Pty Ltd | Baker A.,Defence Science and Technology Organisation, Australia | Baker A.,Cooperative Research Center for Advanced Composite Structures | Bitton D.,Advanced Composite Structures Australia Pty Ltd | And 2 more authors.
International Journal of Adhesion and Adhesives | Year: 2012

This paper describes the development of a proof test to evaluate the through-life integrity of structural adhesive bonds. The test is focussed on adhesively bonded patch repairs for aircraft structure; especially those where flight safety depends on the integrity of the repair patch. The test could be used either as an alternative or as an addition to structural health monitoring of bonded repairs to increase confidence to the extent that they could be certified for application to flight-critical structure. The implementation of the test is as follows: thin coupons of the patch material are bonded to the surface of the parent structure simultaneously with, and therefore under very similar conditions to the repair patch. These coupons are proof tested periodically in shear using a torque wrench. Failure of the coupon below a predetermined proof load provides an indication that the adhesive bond to the patch or (possibly) the patch itself has degraded and should be replaced. It was concluded that this test is a very promising cost-effective approach for detecting defective or deteriorated adhesive bonds; however, to raise the technology readiness level to the extent that it could be considered for aircraft applications more work is required to improve the test database and increase practicality.


Baker A.,Advanced Composite Structures Australia Pty Ltd | Baker A.,Cooperative Research Center for Advanced Composite Structures | Baker A.,Defence Science and Technology Organisation, Australia | Gunnion A.,Advanced Composite Structures Australia Pty Ltd | And 2 more authors.
Journal of Adhesion | Year: 2015

Airworthiness certification is required when bonded repairs are made to primary composite structure in situations where damage has reduced or has the potential to reduce residual strength to below the design ultimate strength. Generally, certification of bonded primary structure poses many difficulties. As most repairs are one-off events meeting these certification requirements is especially challenging since demonstration by testing will generally not be possible or cost-effective. This paper discusses options for addressing the two key issues relating to certification: (a) how to validate initial and enduring bond strength of adhesive bonds, mainly given the inability of conventional non-destructive inspection to provide this assurance and (b) how to develop acceptable generic design allowables for bonded repairs which represent actual failure modes - especially for cyclic loading, since validation by testing of simulated repairs will generally be infeasible. It is concluded that proof testing of bonded repair coupons is a promising approach for validating bond strength and fatigue testing of representative bond joint specimen can provide generic allowables for patch design. For hidden structure or very high value repairs structural health monitoring of repairs based on a strain-transfer approach offers considerable promise. © 2015 Crown copyright.


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 | Year: 2015

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.


Deng S.,University of Sydney | Deng S.,Advanced Composite Structures Australia Pty Ltd | Djukic L.,Advanced Composite Structures Australia Pty Ltd | Djukic L.,Cooperative Research Center for Advanced Composite Structures | And 3 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2015

This paper presents a literature survey on the theoretical backgrounds and the past research efforts in relation to the interactions between certain thermoplastics and epoxies, and their applications in polymer blending, epoxy toughening and composite joining. The main objectives are to understand the possible mechanisms of interfacial adhesion between thermoplastic and thermoset polymers, and also to explore the feasible approaches to improve interfacial adhesion for the purposes of joining fibre reinforced polymer (FRP) composite structures by fusion bonding. Further, it is expected that the review would provide some visions to the potential applications of the thermoplastic-thermoset interfacial interactions for the quick assembly of composite structures in cost-effective manufacturing of composite structures, through the uses of the technologies, such as thermoset composite fusion bonding, welding of thermoplastic composites with thermoset composites, and thermoplastic article attachment on thermoset composites. © 2014 Published by Elsevier Ltd.


Baker A.,Advanced Composite Structures Australia Pty Ltd. | Baker A.,Cooperative Research Center for Advanced Composite Structures | Baker A.,Defence Science and Technology Group | Gunnion A.J.,Advanced Composite Structures Australia Pty Ltd. | And 3 more authors.
International Journal of Adhesion and Adhesives | Year: 2016

The availability of an efficient, cost-effective repair technology is an important maintenance requirement to restore structural integrity to metallic and composite airframe structures damaged in service. Generally repair involves attachment of a reinforcing structural element or patch to replace the damaged load path. Traditionally, the reinforcements are attached to the structure with rivets or bolts; however, attachment by adhesive bonding offers many structural and cosmetic advantages. However, bonded repairs of primary structure are very difficult to certify this is because available non-destructive procedures, such as ultrasonics or thermography are unable to detect weak adhesive bonds. In view of the limitation of non-destructive inspection an alternative approach is to directly apply stress to the actual repair bond region or to a very close simulation of the region. In this paper, further work is documented on a proof test of bonded repair coupons (BRCs) that are bonded to the parent structure at the same time as bonding of the repair patch. Therefore, the BRCs are close representation of the actual repair bond strength. To assess the bond strength, immediately after patch application and also possibly through the life of the repair, the BRCs are subject to a previously determined proof load in torsion. The aim of the study is to improve the Technical Readiness Level of the test when applied to various parent-structure/patch-repair systems, including carbon-epoxy/carbon-epoxy; aluminium/boron-epoxy and aluminium/aluminium. Improved BRC application methods were developed to increase the reliability and consistency of the results, and sensitivity to cure condition, surface treatment, contamination, and fatigue damage were evaluated. A detailed finite element (FE) study was undertaken to: a) simulate stresses in the BRC, adhesive and parent structure during the proof test, b) compare the stresses in the patch and BRC when the parent material is under stress and c) investigate the influence of BRC proximity to the patch tip when the parent material is under stress. A conclusion from the FE analysis and fatigue study was that a BRC with the appropriate ply configuration could represent the bondline stresses experienced at the patch tip, and hence could also be used to monitor fatigue damage. © 2015 Published by Elsevier Ltd. All rights reserved.


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 | Year: 2014

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).


Djukic L.P.,Advanced Composite Structures Australia Pty Ltd | Djukic L.P.,Cooperative Research Center for Advanced Composite Structures Ltd | Sum W.S.,Petronas | Leong K.H.,Petronas | And 5 more authors.
Materials and Design | Year: 2015

In the oil and gas industry, clamps are a common means of repairing pipelines with leaking defects. The use of composite instead of metal presents key advantages in reduced weight, smaller relative density compared to water and greater corrosion resistance. This paper presents two different composite clamp designs, with design pressures of 10.5. MPa, along with test results. The designs differ with respect to the clamp laminate thickness, the clearance gap between the pipe and the clamp, the rubber seal hardness and the test temperature. Test results show that the clamps withstand the design pressure with appreciable margins, at all three temperatures considered, namely room temperature, 65. °C and 80. °C. Generally, the leak containment capacity of the composite clamp increases with greater laminate thickness and seal hardness, and it decreases with greater clearance gap. Finally, the results have successfully demonstrated the design methodology proposed for these clamps. © 2015 Elsevier Ltd.

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