Effect of fiber array irregularities on microscopic interfacial normal stress states of transversely loaded UD-CFRP from viewpoint of failure initiation

• Published in: Composites science and technology Vol. 69; no. 11; pp. 1726 - 1734
• Main Authors: Hojo, Masaki, Mizuno, Masaaki, Hobbiebrunken, Thomas, Adachi, Taiji, Tanaka, Mototsugu, Ha, Sung Kyu
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 01.09.2009; Elsevier
• Subjects: Applied sciences; B. Debonding; C. Finite element analysis (FEA); C. Residual stress; C. Transverse cracking; Exact sciences and technology; Forms of application and semi-finished materials; Laminates; Micromechanics; Polymer industry, paints, wood; Technology of polymers; Micromechanics; B. Debonding; C. Finite element analysis (FEA); C. Residual stress; C. Transverse cracking; Laminate; Unidirectional fiber material; Fiber reinforced material; Epoxy resin; Theoretical study; Mechanical properties; Tensile property; Transverse load; Mineral fiber; Modeling; Composite material; Finite element method; Stress cracking; Numerical simulation; Alignment defect; Carbon fiber
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/j.compscitech.2008.08.032

A detailed investigation has been carried out to determine the effect of local fiber array irregularities and controlling fiber distribution parameters on microscopic interfacial normal stress states for transversely-loaded unidirectional carbon fiber (CF)/epoxy composites. Linear elastic finite element analyses were carried out for two-dimensional image-based models composed of about 70 fibers. The relationship between the geometrical distribution of two adjacent fibers and the interfacial normal stresses (INSs) is investigated for all fibers in different image-based models. Three boundary conditions for loading were selected: Case A involved cooling from the curing temperature (the difference in temperature was −155 K); Case B involved transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength; and Case C involved both cooling from the curing temperature and transverse loading of 75 MPa. High compressive INSs due to the difference in the coefficients of thermal expansion are observed at the location of the shortest interfiber distance for Case A (cooling). High tensile INSs are observed at the location of the shortest interfiber distance and where the fiber alignment angle to the loading direction is small for Case B (loading). For Case C (cooling and loading), the high thermal residual compressive INSs and the high mechanical tensile INSs compensate each other, and the INSs at a short interfiber distance are much lower than those for Case B. These results clearly indicate the importance of the contribution of the thermal residual stresses to the transverse tensile failure initiation of CF/epoxy laminates.