On the application of fracture mechanics to the size scaling of bonded composite lap joints

Research output: Contribution to conferenceAbstract

Abstract

The use of large composite materials in large aircraft structures has been widely adopted within the aerospace industry. In the airframe design process, large scale tests (including large components and full scale tests) are required to capture accurately all possible locations of failure. However, large scale tests are expensive and time consuming, which makes it impractical and inefficient to include every possible failure scenario. Current practice is using a test pyramid so that the number of large scale tests can be reduced with the support of testing small scale coupons and components. However, a crucial question still remains: how to relate the small coupon tests to large scale tests.
Previous work conducted numerical and experimental studies of the size effect upon the strength of fibre reinforced composites. These studies showed a tendency for the strength to decrease with increasing specimen volume, where the Weibull strength theory can give a reasonable representation of the size effect. Based on these researches, size effect can be taken into account using the strength properties from small coupons in the design of large structures. However, very limited amount of information is available for the scaling of composite lap joints, which are the primary structural components of aircraft fuselage made of composites. Since aircraft structures are designed for damage tolerance, effect of process-induced defects in bonded joints should be assessed.
The main objective of this paper is to explore the scalability of fracture phenomena in bonded composite joints. A numerical investigation into size effects in composite single lap joints is carried out under the circumstances of two types of defects (strip and semi-circular defects). The in-plane dimensions of the single lap joints with pre-designed defects are scaled up and the crack tip strain energy release rates (SERRs) are determined by the Virtual Crack Closure Technique (VCCT) using Finite Element Analysis (FEA). The baseline geometry of a standard single lap joint is validated with experiments. The study has found that linear elastic fracture mechanics (LEFM) can be applied to the scaling of fracture process of large scale structures. The values of SERR (and also SERR versus crack length relation) can be scaled linearly with the size of the joints, and thus can be used as a normalizing parameter to relate the initial crack propagation and to bridge the dimension gap between large scale composite joints and scaled down lab joints. This study contributes to the concept of Predictive Virtual Testing (PVT) to predict the actual fatigue fracture behaviour of aircraft structures by finite element method for the purpose of replacing or reducing structural tests.
Original languageEnglish
Publication statusPublished - 9 Oct 2018
Event6th Aircraft Structural Design Conference - We The Curious, Bristol, United Kingdom
Duration: 9 Oct 201811 Oct 2018
https://www.aerosociety.com/events-calendar/6th-aircraft-structural-design-conference/

Conference

Conference6th Aircraft Structural Design Conference
CountryUnited Kingdom
CityBristol
Period9/10/1811/10/18
Internet address

Fingerprint

Fracture mechanics
Composite materials
Energy release rate
Strain energy
Defects
Aircraft
Finite element method
Damage tolerance
Crack closure
Airframes
Fuselages
Aerospace industry
Testing
Crack tips
Scalability
Crack propagation
Fatigue of materials
Cracks
Geometry
Fibers

Cite this

Liu, Y., Lemanski, S., & Zhang, X. (2018). On the application of fracture mechanics to the size scaling of bonded composite lap joints. Abstract from 6th Aircraft Structural Design Conference, Bristol, United Kingdom.

On the application of fracture mechanics to the size scaling of bonded composite lap joints. / Liu, Yiding; Lemanski, Stuart; Zhang, Xiang.

2018. Abstract from 6th Aircraft Structural Design Conference, Bristol, United Kingdom.

Research output: Contribution to conferenceAbstract

Liu, Y, Lemanski, S & Zhang, X 2018, 'On the application of fracture mechanics to the size scaling of bonded composite lap joints' 6th Aircraft Structural Design Conference, Bristol, United Kingdom, 9/10/18 - 11/10/18, .
Liu Y, Lemanski S, Zhang X. On the application of fracture mechanics to the size scaling of bonded composite lap joints. 2018. Abstract from 6th Aircraft Structural Design Conference, Bristol, United Kingdom.
@conference{2eed27b5590e488998e59f7c4ab2981a,
title = "On the application of fracture mechanics to the size scaling of bonded composite lap joints",
abstract = "The use of large composite materials in large aircraft structures has been widely adopted within the aerospace industry. In the airframe design process, large scale tests (including large components and full scale tests) are required to capture accurately all possible locations of failure. However, large scale tests are expensive and time consuming, which makes it impractical and inefficient to include every possible failure scenario. Current practice is using a test pyramid so that the number of large scale tests can be reduced with the support of testing small scale coupons and components. However, a crucial question still remains: how to relate the small coupon tests to large scale tests.Previous work conducted numerical and experimental studies of the size effect upon the strength of fibre reinforced composites. These studies showed a tendency for the strength to decrease with increasing specimen volume, where the Weibull strength theory can give a reasonable representation of the size effect. Based on these researches, size effect can be taken into account using the strength properties from small coupons in the design of large structures. However, very limited amount of information is available for the scaling of composite lap joints, which are the primary structural components of aircraft fuselage made of composites. Since aircraft structures are designed for damage tolerance, effect of process-induced defects in bonded joints should be assessed. The main objective of this paper is to explore the scalability of fracture phenomena in bonded composite joints. A numerical investigation into size effects in composite single lap joints is carried out under the circumstances of two types of defects (strip and semi-circular defects). The in-plane dimensions of the single lap joints with pre-designed defects are scaled up and the crack tip strain energy release rates (SERRs) are determined by the Virtual Crack Closure Technique (VCCT) using Finite Element Analysis (FEA). The baseline geometry of a standard single lap joint is validated with experiments. The study has found that linear elastic fracture mechanics (LEFM) can be applied to the scaling of fracture process of large scale structures. The values of SERR (and also SERR versus crack length relation) can be scaled linearly with the size of the joints, and thus can be used as a normalizing parameter to relate the initial crack propagation and to bridge the dimension gap between large scale composite joints and scaled down lab joints. This study contributes to the concept of Predictive Virtual Testing (PVT) to predict the actual fatigue fracture behaviour of aircraft structures by finite element method for the purpose of replacing or reducing structural tests.",
author = "Yiding Liu and Stuart Lemanski and Xiang Zhang",
year = "2018",
month = "10",
day = "9",
language = "English",
note = "6th Aircraft Structural Design Conference ; Conference date: 09-10-2018 Through 11-10-2018",
url = "https://www.aerosociety.com/events-calendar/6th-aircraft-structural-design-conference/",

}

TY - CONF

T1 - On the application of fracture mechanics to the size scaling of bonded composite lap joints

AU - Liu, Yiding

AU - Lemanski, Stuart

AU - Zhang, Xiang

PY - 2018/10/9

Y1 - 2018/10/9

N2 - The use of large composite materials in large aircraft structures has been widely adopted within the aerospace industry. In the airframe design process, large scale tests (including large components and full scale tests) are required to capture accurately all possible locations of failure. However, large scale tests are expensive and time consuming, which makes it impractical and inefficient to include every possible failure scenario. Current practice is using a test pyramid so that the number of large scale tests can be reduced with the support of testing small scale coupons and components. However, a crucial question still remains: how to relate the small coupon tests to large scale tests.Previous work conducted numerical and experimental studies of the size effect upon the strength of fibre reinforced composites. These studies showed a tendency for the strength to decrease with increasing specimen volume, where the Weibull strength theory can give a reasonable representation of the size effect. Based on these researches, size effect can be taken into account using the strength properties from small coupons in the design of large structures. However, very limited amount of information is available for the scaling of composite lap joints, which are the primary structural components of aircraft fuselage made of composites. Since aircraft structures are designed for damage tolerance, effect of process-induced defects in bonded joints should be assessed. The main objective of this paper is to explore the scalability of fracture phenomena in bonded composite joints. A numerical investigation into size effects in composite single lap joints is carried out under the circumstances of two types of defects (strip and semi-circular defects). The in-plane dimensions of the single lap joints with pre-designed defects are scaled up and the crack tip strain energy release rates (SERRs) are determined by the Virtual Crack Closure Technique (VCCT) using Finite Element Analysis (FEA). The baseline geometry of a standard single lap joint is validated with experiments. The study has found that linear elastic fracture mechanics (LEFM) can be applied to the scaling of fracture process of large scale structures. The values of SERR (and also SERR versus crack length relation) can be scaled linearly with the size of the joints, and thus can be used as a normalizing parameter to relate the initial crack propagation and to bridge the dimension gap between large scale composite joints and scaled down lab joints. This study contributes to the concept of Predictive Virtual Testing (PVT) to predict the actual fatigue fracture behaviour of aircraft structures by finite element method for the purpose of replacing or reducing structural tests.

AB - The use of large composite materials in large aircraft structures has been widely adopted within the aerospace industry. In the airframe design process, large scale tests (including large components and full scale tests) are required to capture accurately all possible locations of failure. However, large scale tests are expensive and time consuming, which makes it impractical and inefficient to include every possible failure scenario. Current practice is using a test pyramid so that the number of large scale tests can be reduced with the support of testing small scale coupons and components. However, a crucial question still remains: how to relate the small coupon tests to large scale tests.Previous work conducted numerical and experimental studies of the size effect upon the strength of fibre reinforced composites. These studies showed a tendency for the strength to decrease with increasing specimen volume, where the Weibull strength theory can give a reasonable representation of the size effect. Based on these researches, size effect can be taken into account using the strength properties from small coupons in the design of large structures. However, very limited amount of information is available for the scaling of composite lap joints, which are the primary structural components of aircraft fuselage made of composites. Since aircraft structures are designed for damage tolerance, effect of process-induced defects in bonded joints should be assessed. The main objective of this paper is to explore the scalability of fracture phenomena in bonded composite joints. A numerical investigation into size effects in composite single lap joints is carried out under the circumstances of two types of defects (strip and semi-circular defects). The in-plane dimensions of the single lap joints with pre-designed defects are scaled up and the crack tip strain energy release rates (SERRs) are determined by the Virtual Crack Closure Technique (VCCT) using Finite Element Analysis (FEA). The baseline geometry of a standard single lap joint is validated with experiments. The study has found that linear elastic fracture mechanics (LEFM) can be applied to the scaling of fracture process of large scale structures. The values of SERR (and also SERR versus crack length relation) can be scaled linearly with the size of the joints, and thus can be used as a normalizing parameter to relate the initial crack propagation and to bridge the dimension gap between large scale composite joints and scaled down lab joints. This study contributes to the concept of Predictive Virtual Testing (PVT) to predict the actual fatigue fracture behaviour of aircraft structures by finite element method for the purpose of replacing or reducing structural tests.

M3 - Abstract

ER -