Matrix Cracking and Residual Strain in CFRP Laminates under Tensile Loading

The effect of thermal cycling on the mechanical properties of composite materials is an important issue in engineering, especially in their applications to the space environment. The present study concerned with the experimental study of both the thermal cycling induced matrix cracking and the effect of thermal cycling on the matrix cracking behavior under tensile loading in CFRP laminates. Two kinds of carbon/epoxy systems, T800H/3631 and T300/2500, are used for the laminate configurations of (0/90)s and (90/0)s. The specimens are thermally cycled between −196 and 100°C. Thermal cycling tests are performed up to 1000 cycles. The polished edge surfaces of specimens are examined by the replica technique, and then the matrix crack density is measured as a function of the number of thermal cycles. It is found that the first matrix cracking in (0/90)s and (90/0)s laminates occurs at almost the same numbers of thermal cycles. It is also found that the matrix crack density increases more rapidly in (0/90)s laminates than in (90/0)s laminates in both material systems. To investigate the effect of thermal cycling on matrix cracking behavior under tensile loading, a series of tensile tests on thermally cycled specimens are performed. The effect of thermal cycling on matrix cracking under tension is evaluated in terms of the change in the critical energy release rate and the critical stress for matrix cracking.

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Measurement of residual strains as a parameter of matrix cracking in CFRP laminates

Journal of Advanced Mechanical Design Systems and Manufacturing ◽

10.1299/jamdsm.2021jamdsm0040 ◽

2021 ◽

Vol 15 (4) ◽

pp. JAMDSM0040-JAMDSM0040

Author(s):

M. J. Mohammad FIKRY ◽

Shinji OGIHARA ◽

Vladimir VINOGRADOV

Keyword(s):

Matrix Cracking ◽

Cfrp Laminates ◽

Residual Strains

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Measurement of Residual Strains As a Parameter of Matrix Cracking in CFRP Laminates

JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing ◽

10.1115/lemp2020-8512 ◽

2020 ◽

Author(s):

M. J. Mohammad Fikry ◽

Shinji Ogihara ◽

Vladimir Vinogradov

Keyword(s):

Viscoelastic Behavior ◽

Matrix Cracking ◽

Time Dependent ◽

Strain Gauges ◽

Recovery Test ◽

Cfrp Laminates ◽

Matrix Cracks ◽

Theoretical Predictions ◽

Residual Strains ◽

Good Agreement

Abstract Matrix cracking in CFRP laminates results in degradation of mechanical properties of the material and appearance of residual strains. In this study, the residual strains investigated are experimentally and analytically for CFRP [0/756]s laminates. The strain gauges were used in this study to measure the strains. Due to very small residual strains at the unloading condition, the residual strains were also measured at different stress levels for laminates with different crack densities and are compared with theoretical predictions. Time-dependent viscoelastic behavior of the material is also considered to accurately measure the residual strains due to the occurrence of matrix cracks. This was done by using the strain recovery test when the loads were stopped for 1–1.5 hours during unloading and the strain changes during these times were recorded. The experimental results of the residual strains are in reasonably good agreement with the theoretical predictions. The fiber non-linearity properties of the laminates may cause some experimental data to shift above the analytical line.

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Correlation Study of IR TNDT Analysis with Structural Failure Modes of Carbon-Fabric-Reinforced Epoxy Composites

Journal of Engineered Fibers and Fabrics ◽

10.1177/155892501501000108 ◽

2015 ◽

Vol 10 (1) ◽

pp. 155892501501000 ◽

Cited By ~ 2

Author(s):

Vasanthanathan Arunachalam ◽

P. Nagaraj

Keyword(s):

Failure Modes ◽

Epoxy Composite ◽

Tensile Loading ◽

Matrix Cracking ◽

Strength Parameter ◽

Uniaxial Tensile ◽

Carbon Fabric ◽

Plane Shear ◽

Microstructural Investigation ◽

Uniaxial Tensile Loading

In the present work, a generic experimental investigation procedure was developed on mechanical characterization and testing of carbon fabric/epoxy material under uniaxial tensile loading condition. In this study, using IR Thermographic NDT, the defects are identified by measuring changes in temperature online during testing and by taking temperature contour images on the surface of the composite samples. The unidirectional elastic properties such as tensile modulus, in-plane shear modulus, Poisson's ratio, and strength parameter like ultimate tensile strength, shear strength are reported. The estimated mechanical properties of carbon fabric/ epoxy composite were statistically analysed in this work using the Weibull distribution. In addition, emphasis on the microstructural investigation using Scanning Electron Microscope (SEM) is given, in order to study the fracture mechanism of the carbon fabric/epoxy composite under uniaxial tensile loading. The failure surfaces of the tensile tested carbon fabric/epoxy specimens were examined by SEM and the detailed fracture process such as matrix cracking, fiber pull outs and delamination are observed and discussed.

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Cluster analysis of acoustic emission signals and tensile properties of carbon/glass fiber–reinforced hybrid composites

Structural Health Monitoring ◽

10.1177/1475921719833467 ◽

2019 ◽

Vol 18 (5-6) ◽

pp. 1686-1697 ◽

Cited By ~ 1

Author(s):

Wen-zheng Zhao ◽

Wei Zhou

Keyword(s):

Acoustic Emission ◽

Digital Image Correlation ◽

Glass Fiber ◽

Digital Image ◽

Hybrid Composites ◽

Correlation Method ◽

Tensile Loading ◽

Image Correlation ◽

Matrix Cracking ◽

Woven Composites

Understanding the damage and failure of carbon/glass epoxy hybrid woven composites under tensile loading based on acoustic emission signals is a challenging task in their practical uses. In this study, an approach based on fuzzy c-means algorithm is proposed to process the acoustic emission signals from tensile loading of composites monitored by combining acoustic emission technology and digital image correlation method. The results show that the acoustic emission signals from tensile loading can be divided into three clusters. The three clusters correspond to three kinds of damage modes including matrix cracking, fiber/matrix debonding, delamination, and fiber breakage. By comparing the acoustic characteristics of these classes, a correlation procedure between the clusters and the damage mechanisms observed is proposed. Meanwhile, it can be found that debonding and fiber break signals for glass fiber correspond to a lower frequency range than that for carbon fiber. Moreover, the method combining acoustic emission and digital image correlation can effectively monitor the damage process of the specimen both on the inside and outside, which can provide a reference for the health monitoring of composite structure.

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