A novel Top Surface Analysis method for Mode I interface characterization using Digital Image Correlation

Significance Statement

Debonding and interlaminar delamination are typical failure modes when it comes to fiber-metal laminates and composites respectively. Accurately characterizing interface properties plays an important role in modeling and improving mechanical attributes of bonded and laminate structures. The Double Cantilever Beam (DCB) test is widely used to determine Mode I interlaminar facture toughness of composite materials and structures. This traditional approach is based on optical tracking of scales hand-marked on the test piece edge. This makes the method prone to uncertainties as it is dependent on human skills. Accurate crack length identification in the determination of the Mode I strain energy release rate is the main challenge, in particular in thin laminates.

In a recent paper published in Engineering Fracture Mechanics Johannes Reiner, Juan Pablo Torres and Martin Veidt at the University of Queensland and the Defence Materials Technology Centre in Australia present a novel Top Surface Analysis (TSA) method that overcomes human errors by a top surface analysis of the DCB test pieces through Digital Image Correlation (DIC). This automated measuring and data analysis approach determines simultaneously crack length and crack tip opening displacement. The method minimizes human errors because it is based on clear-cut post-processing of generated surface data by non-contact DIC. DCB tests were performed with a 10kN load cell at room temperature. The authors set the cross-head displacement rate at 3mm/min and recorded load displacement, which was synchronized with the DIC software Aramis.

The researchers painted a fine speckle pattern on the surface of the test pieces over a selected area of interest. This created a textured pattern on the specimen surface. They set the facet size and distance at 19×19 pixels2 and 16 pixels respectively. Each facet had an overlap distance of 3 pixels with its immediate neighbors. The facet size as well as the quality of the speckle pattern determine the spatial resolution, and consequently the accuracy of the measurements.

The methodology presented in this paper compares the outcomes of the Top Surface Analysis method with those of the manual crack tracking approach that implements optical side-view observation of markings on printed scales.

For carbon fiber reinforced polymer laminates, the authors observed that delamination initiated consistently at around 100N. A typical saw-toothed response in woven composite laminates was observed after the initiation of delamination. This is due to the fiber microstructure that inhibited delamination growth which results in a stick-slip load decrease up to ultimate failure. Seven surface lines on the DCB specimens were analyzed. TSA gave consistent resistance estimation in all the seven surface lines. Conventional side analysis estimated slightly lower Mode I at crack initiation.

For glass fiber reinforced polymer laminates, the authors observed that the delamination initiated at a maximum load of 11-13N. A saw-toothed response was noted during crack propagation. A high resolution side view using DIC gave fractured speckle patterns that led to incomplete pattern recognition. In contrast, TSA guaranteed continuous digital image correlation measurement of the displacement pattern on the top surface. Above all, it was possible to determine the strain energy release rate along the width of the DCB specimen, which was previously only possible in computational studies.

The Top Surface Analysis appears to be a promising candidate for simplifying Double Cantilever Beam analyses while increasing precision and repeatability. This crack length inspection approach and data analysis is simple to set up and to analyze and can be automated.

Surface Analysis method for Mode I interface characterization using Digital Image Correlation (Advances in Engineering)

About The Author

Dr Johannes Reiner is a Postdoctoral Fellow at the Civil Engineering department at the University of British Colombia (UBC) under the supervision of Professor Reza Vaziri. He is also part of the Composites Research Network (CRN) at UBC. He holds a Diploma degree in Applied Mathematics (Dipl.-Math. techn.) from the Karlsruhe Institute of Technology (KIT), Germany in 2012. He joined the composites group at the University of Queensland (UQ) in Australia shortly afterwards to pursue his PhD project on the computational failure modelling in composites and hybrid titanium composite laminates under the guidance of Dr Martin Veidt.

His main areas of expertise are nonlinear finite element analysis, computational damage & failure prediction as well as fracture mechanics in composite structures and hybrid metal-composites. One of his latest major contributions is the development and application of the Advanced Phantom Node Method (APNM) to accurately simulate the interaction of matrix cracking and delamination in composite structures.

About The Author

Dr Juan Pablo Torres joined the University of Queensland as postdoctoral research fellow in 2016. His major research theme is the numerical modelling and prediction of the mechanical behaviour and failure of novel engineering materials. These include: novel hybrid composite structures for aerospace and civil applications, natural fibre reinforced composites and engineering polymers and rubbers.

Dr Torres’ research has a strong focus on the implementation of Finite Element analysis, advanced material constitutive modelling, probabilistic design methodologies and optimization algorithms. Juan also works on the development of optical measurement strategies using Digital Image Correlation (DIC) for the experimental determination of deformation and failure of engineering parts and components.

During his PhD studies in Argentina, he was awarded an Australian Government Endeavour Award to conduct research at the University of Queensland. He has also been awarded a European Comission Eurotango award to conduct research at the Universidad Politécnica de Valencia in Spain and the Johannes Kepler Universität in Austria.

About The Author

Dr Martin Veidt is Reader in Applied Mechanics at the University of Queensland in Brisbane, Australia. He received his PhD in 1991 from the Swiss Federal Institute of Technology in Zurich, Switzerland. He has also held positions at Cornell University, University of Bordeaux, City University of Hong Kong and the Swiss Federal Laboratories for Materials and Research.

Dr Veidt’s special areas of expertise and research interests are through-life support of composite materials and structures. This includes quantitative non-destructive evaluation and imaging using ultrasonics, guided wave ultrasonics, non-linear ultrasonics as well as ultrasonic structural health management. Dr Veidt has also made important contributions in the areas of micro mechanical damage modelling and explicit finite element analysis developing and validating new simulation methodologies.

Dr Veidt is coordinating the partnership with the Australian Defence Materials Technology Centre in the areas of light weighting and functional materials, and hi is representing the composites and structural health monitoring research areas in the Centre for Advanced Materials Processing and Manufacturing (AMPAM) at UQ. He has established the UQ Composites research group, which is investigating next generation composites technologies, including thermoplastic matrix composites, hybrid composites and smart materials and structures. Dr Veidt is also using his expertise in applied mechanics to collaborate with colleagues from different fields.

Reference

Johannes Reiner12, Juan Pablo Torres1,3 , Martin Veidt1,2,3 . A novel Top Surface Analysis method for Mode I interface characterization using Digital Image Correlation. Engineering Fracture Mechanics, volume 173 (2017), pages 107–117.

Show Affiliations

1 School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD 4072, Australia

2 Queensland Centre for Advanced Materials Processing and Manufacturing (AMPAM), The University of Queensland, Brisbane, QLD 4072, Australia

3 Defence Materials Technology Centre, Hawthorn, Victoria 3122, Australia  

 

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