Material Characterization of Carbon Fiber Reinforced Polymer Laminate Using Virtual Fields Method

Material Characterization of Carbon Fiber Reinforced Polymer Laminate Using Virtual Fields Metho

Whole-field strain analysis and damage assessment of adhesively bonded patch repair of CFRP laminates using 3D-DIC and FEA

The problem of damage evolution in composite structures, the way it propagates, performance and behavior is of paramount importance in utilizing them for structural applications. In the present work, an experimental study is carried out using digital image correlation (DIC) technique to analyze the behavior of adhesively bonded patch repair of carbon/epoxy unidirectional composite laminates under tensile loading. The damaged panel is repaired with both double and single sided circular patch made of same parent material. Damage initiation and propagation in notched and repaired panel as well as patch debonding is studied using 3D-DIC. Also a 3-D finite element analysis is carried out and obtained strain values are compared with the experimental prediction. They are found to be in good agreemen

Design of optimum patch shape and size for bonded repair on damaged Carbon fibre reinforced polymer panels

Carbon fibre reinforced polymer (CFRP) composite laminates have become popular for structural applications as they are lighter, stronger and tougher. But they are also susceptible to damage while in service. Damage in composite structures reduces its structural integrity and hence the service life. For improved service life, the damages need to be repaired so that structural integrity is restored. Adhesively bonded composite patch repair is one of the prominent technique used for restoring the structural integrity of the damaged part. Patch shape is one of the important parameter in composite repair performance and it needs to be investigated thoroughly. In the present work, a 3D finite element based study is carried out to investigate the influence of various patch shapes on repair efficiency. Damaged CFRP laminates are repaired by symmetrical patch adhesively bonded over the damaged area. The panel analyzed is of pure unidirectional and quasi-isotropic laminate sequences. The patch shapes considered are circle, rectangle, square, ellipse, octagon and oval. Stress concentration factor (SCF) is estimated before and after the repair to evaluate their efficiency. Also peel stress is considered for quantitative comparison. The SCF reduction and peel stress are compared for various patch shapes keeping constant patch volume. Stress based 3D-Hashin’s failure criterion is employed for predicting the strength at damage initiation along with failure modes in notched and repaired panel. Optimal patch shape is then brought-out based on higher repair efficiency. Finally, a genetic algorithm based approach in-conjunction with finite element analysis is used for the optimization of patch geometry and adhesive thickness in order to obtain higher repair performance

Assessment of local strain field in adhesive layer of an unsymmetrically repaired CFRP panel using digital image correlation

The present study focuses on experimental investigation of through the thickness displacement and strain field in thin adhesive layer in single sided (unsymmetrical) patch repaired CFRP (carbon fiber reinforced polymer) panel under tensile load. Digital image correlation (DIC) technique is employed to acquire the displacement and strain (longitudinal, peel and shear) field. Experimental determination of shear transfer length based on shear strain field obtained from DIC is introduced to estimate the optimum overlap length which is an essential parameter in patch design for the repair of CFRP structures. Further, DIC experiment with magnified optics is performed to get an insight into complex and localized strain field over thin adhesive layer especially at critical zones leading to damage initiation. The failure mechanism, load displacement behavior, damage initiation and propagation are closely monitored using DIC. The influence of patch edge tapering on strain distribution in adhesive layer is also investigated. The DIC successfully captures the global and localized strain field at critical zones over thin adhesive layer and further helps in monitoring the damage based on strain anomalies. Strains are found to have maximum magnitude at the patch overlap edge and the shear strain level in adhesive layer is higher than the peel strain. Normal tapering increases the peel strain and has negligible influence on shear strain level in adhesive layer. The recommended overlap length is found to be consistent with the recommendation in the literature. Whole field strain pattern and the overlap length obtained from experiment are further compared with the finite element analysis results and they appear to be in good coherence

An experimental and numerical investigation of progressive damage analysis in bonded patch repaired CFRP laminates

The damage evolution in composite material is a complex phenomenon, comprising several interacting failure modes like matrix cracking, fiber breakage, debonding and delamination. Damage initiation, its propagation and ultimate strength prediction of composite structure is of paramount importance for developing reliable and a safer design and utilizing them as primary load bearing one. During service life, these structures get damaged and are often repaired for extending their service life. In the present work, a 3D finite element-based progressive damage model is developed for predicting the failure and post-failure behaviour of notched and repaired panel under tensile load. Failure initiation load, ultimate strength and failure mechanisms are investigated through the developed progressive damage model. The accuracy of developed finite element model is assessed by comparing its prediction with the experimental results obtained from digital image correlation technique and they are found to be in good agreement. In this study, the panels made of carbon/epoxy composite laminates of pure unidirectional and quasi-isotropic stacking sequence are considered. The damaged panel is repaired with both single- and double-sided circular patch of same parent material. Stress-based 3D-Hashin's failure criterion is used for predicting the damage mechanism. Maximum shear stress and strain criteria are considered to account for patch debonding. It is found that the damage in notched panel always initiates with matrix cracking around the hole. However, damage in repaired panel is influenced by localized patch debonding

Whole field strain measurement in critical thin adhesive layer of single and double sided repaired CFRP panel using DIC

In the present work, the behavior of thin adhesively layer in patch repaired carbon fiber reinforced polymer (CFRP) panel under tensile load is investigated experimentally using digital image correlation (DIC) technique. The panel is made of Carbon/epoxy composite laminate and the stacking sequence in the panel is NT. A circular hole of 10 mm diameter (d) is drilled at the center of the panel to mimic the case of low velocity impact damage removal. The panel with open hole is repaired with double sided (symmetrical) and single sided (unsymmetrical) rectangular patch made of same panel material having stacking sequence of pl. Araldite 2011 is used for bonding the patch onto the panel over the damaged area. The global behavior of thin adhesive layer is examined by analyzing whole field strain distribution using DIC. Longitudinal, peel and shear strain field in both double and single sided repair configuration is studied and a compression is made between them. An estimate of shear transfer length which is an essential parameter in arriving at an appropriate overlap length in patch design is proposed from DIC and FEA. Damage development, failure mechanism and load displacement behavior is also investigated. The experimental results are compared with the numerical predictions

Critical analysis of adhesive layer behavior in patch-repaired carbon fiber-reinforced polymer panel involving digital image correlation

In the present work, critical strain field in thin adhesively layer of double-sided (symmetrical) patch-repaired carbon fiber-reinforced polymer composite panel under tensile load is investigated using digital image correlation technique. Longitudinal, peel, and shear-strain distribution in adhesive layer is analyzed thoroughly in repaired panel by performing global cum local strain field analysis involving digital image correlation. Effective load/shear transfer length in repair configuration is estimated based on global strain analysis, and further, it is compared with the one predicted from finite-element analysis. Localized strain analysis using magnified optics provides higher resolution, and it is found useful in revealing complex strain field in small but critical zones responsible for failure initiation. The global and local-strain analyses are found complementary to one another, and therefore both are essential to fully characterize the strain field in thin-adhesive layer. The critical failure mechanism is also investigated and correlated with the load–displacement behavior. DIC is found to be suitable and accurate for analyzing the global and local strain field over small but critical locations and helps in predicting the damage-initiation location based on strain anomalies. Finally, the experimental results are compared with the numerical predictions, and they are found to be in good correlation

Strength prediction and progressive failure analysis of carbon fiber reinforced polymer laminate with multiple interacting holes involving three dimensional finite element analysis and digital image correlation

Composites are finding lot of applications in aerospace, automobile and many other sectors due to their high strength to weight ratio and longer fatigue life. For assembly or electrical wiring purposes, often hole(s) are drilled into the laminate thereby reducing its strength. The strength prediction and damage mechanics study is of great importance in such structural applications. In this work, a three-dimensional finite element based progressive damage model (PDM) is presented for unidirectional carbon fiber reinforced polymer (CFRP) laminates having two holes in different configurations subjected to tensile loading. The developed model is suitable for predicting failure and post failure behavior of fiber reinforced composite materials. The material is assumed to behave as linear elastic until final failure. The three broad steps involved in this study are stress analysis, failure analysis and damage propagation which are implemented as a PDM involving finite element analysis. Hashin's failure criteria for unidirectional fiber composite is used for the damage prediction. It utilizes a set of appropriate degradation rules for modeling the damage involving material property degradation method. Digital image correlation (DIC) experiment is also carried out to perform whole field strain analysis of CFRP panel with different hole configurations. Whole field surface strain and displacement from finite element prediction are compared with DIC results for validation of the finite element model. Load-deflection behavior as well as path of damage progression is predicted by both PDM simulation and experiment. They are found to be in good agreement thereby confirming the accuracy of PDM implementation. Effect of spacing between the holes on stress concentration factor (SCF) is also further investigate