The research of the residual stress influence on unidirectional composite materials mechanical properties through micromechanical analysis.
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Qingchuan LIU (CHINA), Xiaodong WANG (CHINA), Zhidong GUAN , Zengshan LIAbstract :
Background:
Residual stress (RS) in CRFP composites arise from varying properties of component materials during manufacturing, affecting their failure strength and mechanisms. Understanding and evaluating RS through quantitative analysis is vital for assessing composite materials' mechanical performance.
Methods:
In this study, viscoelastic properties were ascertained through Dynamic Mechanical Analysis (DMA), and thermal expansion coefficients of fully cured resin were measured. A finite element model using representative volume elements was developed, incorporating periodic boundary conditions for stress continuity. Mechanical performance, including load-bearing and failure behaviors of fibers, matrix, and their interface, was examined. A novel approach was proposed for incorporating residual stress into the mechanical analysis model using a pre-loaded stress field. This model was applied to analyze unidirectional plates under transverse tension, compression, and longitudinal shear to understand the damage patterns and stress/strain evolution due to residual stress.
Results & discussion:
The study involved fitting the viscoelastic parameters and thermal expansion coefficients of materials, determining a characteristic temperature for the simplified viscoelastic constitutive model considering stress relaxation. Residual stress simulation was based on this model. Analysis revealed that due to the lower transverse thermal expansion coefficient of fibers compared to the matrix, the matrix was under tensile stress while fibers were compressed. In unidirectional plates, there were notable tensile and compressive stress around fibers in the matrix. Longitudinal shear residual stress was nearly absent in-plane due to the lack of shear deformation during the curing process of unidirectional plate.
The study of mechanical performance focused on transverse tension, compression, and longitudinal shear. Residual stress in transverse tension caused early plastic deformation and initial damage in the matrix, leading to higher overall damage strain and ultimate strength. In transverse compression, residual stress slightly advanced initial matrix damage, marginally reducing overall damage strain and strength. longitudinal shear was minimally affected by residual stress due to the absence of a shear component in the stress, leaving ultimate strength and failure load largely unchanged.
Conclusion:
The research established viscoelastic parameters for simulating residual stress in composite materials. It identified residual stress distribution in 90° unidirectional plates and incorporated this into a microscale model for damage analysis under various loads. The study revealed that residual stress enhance strength in transverse tension, slightly reduce strength and damage strain in compression, and marginally increase damage strain in longitudinal shear without significantly affecting ultimate strength.
Residual stress (RS) in CRFP composites arise from varying properties of component materials during manufacturing, affecting their failure strength and mechanisms. Understanding and evaluating RS through quantitative analysis is vital for assessing composite materials' mechanical performance.
Methods:
In this study, viscoelastic properties were ascertained through Dynamic Mechanical Analysis (DMA), and thermal expansion coefficients of fully cured resin were measured. A finite element model using representative volume elements was developed, incorporating periodic boundary conditions for stress continuity. Mechanical performance, including load-bearing and failure behaviors of fibers, matrix, and their interface, was examined. A novel approach was proposed for incorporating residual stress into the mechanical analysis model using a pre-loaded stress field. This model was applied to analyze unidirectional plates under transverse tension, compression, and longitudinal shear to understand the damage patterns and stress/strain evolution due to residual stress.
Results & discussion:
The study involved fitting the viscoelastic parameters and thermal expansion coefficients of materials, determining a characteristic temperature for the simplified viscoelastic constitutive model considering stress relaxation. Residual stress simulation was based on this model. Analysis revealed that due to the lower transverse thermal expansion coefficient of fibers compared to the matrix, the matrix was under tensile stress while fibers were compressed. In unidirectional plates, there were notable tensile and compressive stress around fibers in the matrix. Longitudinal shear residual stress was nearly absent in-plane due to the lack of shear deformation during the curing process of unidirectional plate.
The study of mechanical performance focused on transverse tension, compression, and longitudinal shear. Residual stress in transverse tension caused early plastic deformation and initial damage in the matrix, leading to higher overall damage strain and ultimate strength. In transverse compression, residual stress slightly advanced initial matrix damage, marginally reducing overall damage strain and strength. longitudinal shear was minimally affected by residual stress due to the absence of a shear component in the stress, leaving ultimate strength and failure load largely unchanged.
Conclusion:
The research established viscoelastic parameters for simulating residual stress in composite materials. It identified residual stress distribution in 90° unidirectional plates and incorporated this into a microscale model for damage analysis under various loads. The study revealed that residual stress enhance strength in transverse tension, slightly reduce strength and damage strain in compression, and marginally increase damage strain in longitudinal shear without significantly affecting ultimate strength.