Characterization of Fatigue Induced Damage Evolution in CFRPs Using DIC
01 Jan 2017-pp 75-82
TL;DR: In this article, the maximum transverse strain obtained from a curve fit to each set of continuous cycles was used to quantify the damage in terms of local transversal strain, which can in turn be used to validate any developed damage models.
Abstract: Damage evolution in fatigue tests (R = 0.5, −1, 2) conducted on carbon fiber reinforced plastic (CFRP) composites has been characterized using digital image correlation (DIC). Since damage initiation/delamination is a local phenomenon affecting transverse strain more than the longitudinal, local transverse strain is a better indicator of onset of delamination and its propagation. Variation of transverse strain near the initiated delamination with cycles indicates that the damage evolution occurs over 2–3 stages. Each stage has a stable damage growth with sudden increase between the stages. Waviness and the associated error due to the lag between image and load data acquisition was overcome by plotting the maximum transverse strain obtained from a curve fit to each set of continuous cycles. Error due to large relative deformations was avoided by choosing different reference images for different stages. Extent of damage zone and its evolution was characterized by the length over which the transverse strain exceeds a limiting value, which was taken to be that at the end of first stage in the plot. Rate at which the damage propagates shows similar variation as that of the local transverse strain, which shows that the latter can be used as an indicator of fatigue damage evolution. This also provides a method to quantify the damage in terms of local transverse strain, which can in turn be used to validate any developed damage models.
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26 Mar 2009TL;DR: In this paper, a comprehensive overview of image correlation for shape, motion and deformation measurements is provided. But, the authors do not discuss the effect of out-of-plane motion on 2D measurements.
Abstract: Image Correlation for Shape, Motion and Deformation Measurements provides a comprehensive overview of data extraction through image analysis. Readers will find and in-depth look into various single- and multi-camera models (2D-DIC and 3D-DIC), two- and three-dimensional computer vision, and volumetric digital image correlation (VDIC). Fundamentals of accurate image matching are described, along with presentations of both new methods for quantitative error estimates in correlation-based motion measurements, and the effect of out-of-plane motion on 2D measurements. Thorough appendices offer descriptions of continuum mechanics formulations, methods for local surface strain estimation and non-linear optimization, as well as terminology in statistics and probability. With equal treatment of computer vision fundamentals and techniques for practical applications, this volume is both a reference for academic and industry-based researchers and engineers, as well as a valuable companion text for appropriate vision-based educational offerings.
2,454 citations
TL;DR: In this paper, acoustic emission (AE) measurements along the gauge length indicated important critical intra and inter laminar damage occurring as early as 27% of ultimate tensile strength (UTS), typically 0.3% ultimate strain, for laminates with 90° layers.
142 citations
Book•
24 Apr 2002
TL;DR: In this paper, the authors present an approach for the analysis of composite material strength evolution in the presence of failure and failure modes, and demonstrate the effects of failure modes on the strength of composite materials.
Abstract: Preface. Introduction: Basic Thesis. I.1 Elements of the Approach. I.2 Basic Concepts. I.3 Nonuniform Stress States: Characteristic Material Dimensions. I.4 Strength Evolution. I.5 Outline of the Methodology. I.6 Virtual Design. References. 1 Physical Behavior. 1.1 Continuous Fiber Composite Materials. 1.2 Damage Tolerance and Durability. 1.3 Damage Modes and Failure Modes. 1.4 Summary of Concepts. References. 2 Engineering Concepts of Strength. 2.1 Factors That Determine Composite Material Strength. 2.2 Strength under Multiaxial Loading.2.3 Failure Functions for Damage Accumulation. References. Exercises. 3 Strength Evolution. 3.1 Nature of the Problem. 3.2 Progressive Failure. 3.3 Failure Modes. 3.4 Remaining Strength under Long Term Loading. 3.5 Features of Strength Evolution Integral. 3.6 Summary of Approach. References. Exercises. 4 Micromechanical Models of Composite Stiffness and Strength. 4.1 Axial Tensile Strength of Unidirectional Composites. 4.2 Compression Strength. 4.3 Transverse Strength and Shear Strength. References. Exercises. 5 Stiffness Evolution. 5.1 Problem Definition. 5.2 Stiffness Change Due to Matrix Cracking. 5.3 Time Dependent Stiffness Change. 5.4 Temperature Dependent Stiffness Change. 5.5 Summary. References. Exercises. 6 Strength Evolution During Damage Accumulation. 6.1 Problem Definition. 6.2 Factors That Influence Strength. 6.3 Models of Strength Evolution. 6.4 Application Example. References. Exercises.7 Nonuniform Stress States. 7.1 Problem Definition. 7.2 Laminate Edge Related Stresses. 7.3 Undamaged Notched Strength. 7.4 Notched Strength After Damage. 7.5 Fracture Mechanics and Energy Methods. References. Exercises. 8 Example Applications and Case Studies. 8.1 Example: Unnotched Failure of Polymer Composite. 8.2 Case Study 1: Fatigue Behavior of APC 2 Laminates. 8.3 Case Study 2: Elevated Temperature Fatigue Behavior of Graphite FiberA-PPS Laminates. 8.4 Case Study 3: Elevated Temperature Fatigue Behavior of Nextel 610... AluminaA-Yttria Composites. 8.5 Case Study 4: Elevated Temperature Fatigue Behavior of NicalonA-Enhanced SiC Composites. 8.6 Case Study 5: Fatigue Failure of a Structural Composite Shape. 8.7 Summary. References. Appendix to Chapter 1. Index.
111 citations
TL;DR: In this article, the changes in Poisson's ratio and longitudinal modulus as a result of transverse ply cracking in simple crossply GFRP and CFRP laminates are examined experimentally and theoretically.
110 citations
TL;DR: In this article, an acoustic emission (AE) technique has been used to identify the stages of fatigue damage in composites, and the results of the experiments show three distinct stages of damage before the final failure of coupons.
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