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Papers by Alex Harman

Research paper thumbnail of Thermoelastic Stress Analysis of Impacted Composite Laminates for Damage Tracking and Fatigue Life Assessment

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of single-lap countersunk fastened composite joints in bearing using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Post-Impact Fatigue Durability Assessment of Composite Laminates for Enhanced Aircraft Sustainment

Research paper thumbnail of Discrete damage modelling of impacted composites using enhanced ultrasonic inspection data

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of adhesively bonded composite clamped tapered beam specimens with manufacturing induced defects using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of compression after impact strength of composites at elevated temperature using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of The effect of service-induced dent damage on the out-of-plane strength and fatigue durability of metallic honeycomb sandwich structures

Honeycomb has long been recognised as an excellent lightweight structural material because of its... more Honeycomb has long been recognised as an excellent lightweight structural material because of its strength and stiffness, particularly in sandwich structure. In service, however, sandwich structure is particularly susceptible to dent damage from tool drops and foreign object impact. The current paper describes the effect of dents on the out-of-plane mechanical performance of aluminium alloy sandwich honeycomb structure. A coupon-level test program employed static and fatigue loading of sandwich structure to assess the effect of representative dent damage on metallic-skinned control surfaces of high performance military aircraft. Testing has shown that relatively shallow dents are associated with a region of crushed core directly beneath the dent, which leads to large reductions in transverse strength and stiffness. Furthermore, representative fatigue loading leads to failure through the crushed core region. The results indicate the sensitivity of honeycomb structure to impact damage...

Research paper thumbnail of Preliminary numerical assessment of composite laminate repeated load durability following low velocity impact for enhanced aircraft sustainment

Research paper thumbnail of Numerical and Experimental Assessment of a Modified Transverse Cut Tension (TCT) Specimen for In-Situ Loaded X-Ray Computed Tomography of Mode II Dominated Composite Damage Progression

The principal means by which delamination may progress in appropriately designed composite aerosp... more The principal means by which delamination may progress in appropriately designed composite aerospace structures is via Mode II fracture. This can arise near bolted and bonded joints, following in-service damage such as impact or following the inclusion of integrated electronics into the composite structure and manufacture-induced defects. A new specimen type based on the Transverse Cut Tension (TCT) test is proposed to allow the use of in-situ X-ray micro-computed tomography for observation of mode II fracture processes. The tomography seeks to non-destructively observe the progression of three dimensional crack front features that cannot be seen in typical aerospace composite tests. The paper comprises an account of the design using analytic and finite element methods and preliminary experimental verification. The results showed that the measured toughness of the miniaturized specimen compared well with published results for this material in the literature. In addition, a small per...

Research paper thumbnail of A global-local discrete damage modeling framework for composite laminates

AIAA Scitech 2019 Forum

A global-local analysis method is demonstrated within the Regularized eXtended Finite Element (Rx... more A global-local analysis method is demonstrated within the Regularized eXtended Finite Element (Rx-FEM) framework. Rx-FEM is a Discrete Damage Modeling (DDM) method for progressive failure analysis, which introduces displacement discontinuities to represent matrix cracks and delaminations within composite materials. The global-local approach allows for the damage analysis of a localized region within a much larger domain for which stress analysis has already been performed. Two different case studies including static and fatigue analysis were addressed in this work. Results demonstrate that the global-local approach reduces the computational cost in comparison to high fidelity large scale structural analysis and produces reliable results. The present framework is limited global to local scale communication only.

Research paper thumbnail of Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Test

Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Tes... more Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Test Executive Summary DSTO, in collaboration with the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS), is developing the capability to replace ...

Research paper thumbnail of Impact damage tolerance of composite repairs to highly-loaded, high temperature composite structures

Composites Part A: Applied Science and Manufacturing, 2011

In substantiating the strength of highly-loaded composite structure for aerospace application, co... more In substantiating the strength of highly-loaded composite structure for aerospace application, consideration must be given to the effect of in-service damage on the residual strength. The same consideration is not given to repaired structure, which may be non-conservative, especially if the aircraft were to have a repair installed early on in the life of type. The current study aims to

Research paper thumbnail of Improved design methods for scarf repairs to highly strained composite aircraft structure

This paper presents an analytical method to optimise the profile of the scarf joint between dissi... more This paper presents an analytical method to optimise the profile of the scarf joint between dissimilar modulus adherends so that adhesive stresses are approximately uniform along the joint. The optimised scarf repair is expected to enhance joint strength and reduce the amount of material removal. Finite element analyses have been performed to both validate the optimal solution and to evaluate the use of low stiffness patch to repair carbon epoxy composites. In particular, the influence of patch lay-up on adhesive stresses has been investigated.

Research paper thumbnail of Thermoelastic Stress Analysis of Impacted Composite Laminates for Damage Tracking and Fatigue Life Assessment

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of single-lap countersunk fastened composite joints in bearing using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Post-Impact Fatigue Durability Assessment of Composite Laminates for Enhanced Aircraft Sustainment

Research paper thumbnail of Discrete damage modelling of impacted composites using enhanced ultrasonic inspection data

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of adhesively bonded composite clamped tapered beam specimens with manufacturing induced defects using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of Enhanced failure prediction of compression after impact strength of composites at elevated temperature using discrete damage modelling

AIAA SCITECH 2022 Forum, 2022

Research paper thumbnail of The effect of service-induced dent damage on the out-of-plane strength and fatigue durability of metallic honeycomb sandwich structures

Honeycomb has long been recognised as an excellent lightweight structural material because of its... more Honeycomb has long been recognised as an excellent lightweight structural material because of its strength and stiffness, particularly in sandwich structure. In service, however, sandwich structure is particularly susceptible to dent damage from tool drops and foreign object impact. The current paper describes the effect of dents on the out-of-plane mechanical performance of aluminium alloy sandwich honeycomb structure. A coupon-level test program employed static and fatigue loading of sandwich structure to assess the effect of representative dent damage on metallic-skinned control surfaces of high performance military aircraft. Testing has shown that relatively shallow dents are associated with a region of crushed core directly beneath the dent, which leads to large reductions in transverse strength and stiffness. Furthermore, representative fatigue loading leads to failure through the crushed core region. The results indicate the sensitivity of honeycomb structure to impact damage...

Research paper thumbnail of Preliminary numerical assessment of composite laminate repeated load durability following low velocity impact for enhanced aircraft sustainment

Research paper thumbnail of Numerical and Experimental Assessment of a Modified Transverse Cut Tension (TCT) Specimen for In-Situ Loaded X-Ray Computed Tomography of Mode II Dominated Composite Damage Progression

The principal means by which delamination may progress in appropriately designed composite aerosp... more The principal means by which delamination may progress in appropriately designed composite aerospace structures is via Mode II fracture. This can arise near bolted and bonded joints, following in-service damage such as impact or following the inclusion of integrated electronics into the composite structure and manufacture-induced defects. A new specimen type based on the Transverse Cut Tension (TCT) test is proposed to allow the use of in-situ X-ray micro-computed tomography for observation of mode II fracture processes. The tomography seeks to non-destructively observe the progression of three dimensional crack front features that cannot be seen in typical aerospace composite tests. The paper comprises an account of the design using analytic and finite element methods and preliminary experimental verification. The results showed that the measured toughness of the miniaturized specimen compared well with published results for this material in the literature. In addition, a small per...

Research paper thumbnail of A global-local discrete damage modeling framework for composite laminates

AIAA Scitech 2019 Forum

A global-local analysis method is demonstrated within the Regularized eXtended Finite Element (Rx... more A global-local analysis method is demonstrated within the Regularized eXtended Finite Element (Rx-FEM) framework. Rx-FEM is a Discrete Damage Modeling (DDM) method for progressive failure analysis, which introduces displacement discontinuities to represent matrix cracks and delaminations within composite materials. The global-local approach allows for the damage analysis of a localized region within a much larger domain for which stress analysis has already been performed. Two different case studies including static and fatigue analysis were addressed in this work. Results demonstrate that the global-local approach reduces the computational cost in comparison to high fidelity large scale structural analysis and produces reliable results. The present framework is limited global to local scale communication only.

Research paper thumbnail of Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Test

Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Tes... more Structural Analyses of a Demonstrator Composite Replacement Panel in a F-111C Cold Proof Load Test Executive Summary DSTO, in collaboration with the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS), is developing the capability to replace ...

Research paper thumbnail of Impact damage tolerance of composite repairs to highly-loaded, high temperature composite structures

Composites Part A: Applied Science and Manufacturing, 2011

In substantiating the strength of highly-loaded composite structure for aerospace application, co... more In substantiating the strength of highly-loaded composite structure for aerospace application, consideration must be given to the effect of in-service damage on the residual strength. The same consideration is not given to repaired structure, which may be non-conservative, especially if the aircraft were to have a repair installed early on in the life of type. The current study aims to

Research paper thumbnail of Improved design methods for scarf repairs to highly strained composite aircraft structure

This paper presents an analytical method to optimise the profile of the scarf joint between dissi... more This paper presents an analytical method to optimise the profile of the scarf joint between dissimilar modulus adherends so that adhesive stresses are approximately uniform along the joint. The optimised scarf repair is expected to enhance joint strength and reduce the amount of material removal. Finite element analyses have been performed to both validate the optimal solution and to evaluate the use of low stiffness patch to repair carbon epoxy composites. In particular, the influence of patch lay-up on adhesive stresses has been investigated.

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