A Strain Rate Dependent Progressive Damage Model for Carbon Fiber Woven Composites under Low Velocity Impact

A progressive damage model was presented for carbon fiber woven composites under low velocity impact, considering the strain rate sensitivity of both mechanical properties and failure mechanisms. In this model, strain rate dependency of elastic modulus and nominal strength along in-plane direction are considered. Based on the Weibull distribution, stiffness progressive degradation is conducted by introducing strain rate dependent damage variables for distinct damage modes. With the model implemented in ABAQUS/Explicit via user-defined material subroutine (VUMAT), the mechanical behavior and possible damage modes of composites along in-plane direction can be determined. Furthermore, a bilinear traction separation model and a quadratic stress criterion are applied to predict the initiation and evolution of interlaminar delamination. Comparisons are made between the experimental results and numerical simulations. It is shown that the mechanical response and damage characteristics under low velocity impact, such as contact force history and delamination, are more consistent with the experimental results when taken the strain rate effect into consideration.

An Advanced Finite Element Modeling for the Failure of Notched Ceramic Matrix Composite With TFP Patch Reinforcement

An advanced modeling strategy for notched ceramic matrix composite coupons with patch reinforcement was proposed to investigate the failure mechanisms. This model considered the tailored fiber–placed (TFP) yarn details obtained from the design phase and the embedded element concept which was used to successfully overcome the meshing difficulties. Inter-ply “glue” layers were simulated using the surface-based contact cohesive element method, so the delamination due to interfacial material discontinuity and damage can be well reproduced and analyzed. For composite ply, the energy-based composite progressive damage model that is independent of the mesh size was applied. Virtual test campaign was performed with a variety of geometrical and material parameters, and the damage and failure mechanisms based on the stress analysis can be revealed to support the design optimization of patch reinforcement.

A new progressive damage model for predicting the tensile behavior of the three-dimensional woven carbon/carbon composites using micromechanics method

A new progressive damage model for the three-dimensional (3 D) woven carbon/carbon (C/C) composites is developed at fiber-matrix level using the micromechanics method. A woven architecture based Representative Volume Element (RVE) model composed of yarns, matrix and yarn/matrix interface is constructed, in which the manufacturing void defects are accounted for. The fiber-matrix concentric cylinder model is employed as a repeating unit cell to represent the yarn, and the matrix micro strain field is computed analytically by the micromechanics method. The maximum stain criteria is utilized for fiber longitudinal breakage, and the Von-Mises criterion is applied for the damage initiation of matrix in both intra-yarns and inter-yarns. The damaged fiber and matrix are modeled by the stiffness degradation method combined with exponential damage evolution equations. The zero thickness cohesive elements governed by bilinear traction-separation constitutive are adopted for yarn/matrix interfacial debonding behavior. The micro progressive damage and failure behavior of the 3 D woven C/C composites subjected to tension is implemented through a developed user-defined material subroutine in commercial software ABAQUS. The predicted stress-strain response is in a good agreement with experimental results. In addition, the effect of manufacturing void defects is also examined by the developed model.

Burst Pressure of Glass Fiber Tape Reinforced Polyethylene Pipes with Interlayer Delamination Defect

Glass fiber tape reinforced polyethylene (GFTRP) pipes are widely used for the transportation of oil and high pressure gas due to their good load bearing capacity and environmental adaptability. Delamination defect is one of the most common defects of GFTRP pipes during manufacturing and service. This paper investigates the load bearing capacity of GFTRP pipe with interlayer delamination defect in between glass fiber tapes, via a combined experimental and numerical method. In the burst experiments, GFTRP pipes with layup of [±55°]12 were prepared with the artificial delamination defects set in between the 6th and 7th plies. In the numerical model, we used progressive damage model and cohesive element method to analysis the failure of GFTRP pipe with interlayer delamination defect. The results show that both the widths and axial locations of interlayer delamination defects will affect the burst pressure of GFTRP pipe, and the numerical analysis results are in good consistency with experiments. Ultimately, the influence of defect width and location on the burst pressure of GFTRP pipe was discussed in detail.

A progressive damage model of composite laminates under low-velocity impact

In this paper, a progressive damage model for studying the dynamic mechanical response and damage development of composite laminates under low-velocity impact was established. The model applied the Hashin and Hou failure criteria to predict the initiation of intra-laminar damage (fiber and matrix damage); a linear degradation scheme combined with the equivalent displacement method was adopted to simulate the damage development; a cohesive zone model with the bilinear traction-separation relationship was used to predict delamination. A user material subroutine VUMAT was coded, and the simulation analysis of carbon fiber reinforcement composite laminates subjected to 25 J impact was performed via commercial software ABAQUS. The predicted impact force-time curve, impact force-displacement curve, and damage distribution contours among the layers were in a good agreement with the experimental, which verified the proposed model. According to the simulation results, the fiber damage and matrix damage were analyzed, and the expansion of delamination was discussed.

Influence of gap filling on mechanical properties of composite-aluminum single-lap single-bolt hybrid joints

Composite-aluminum structures exist in aircraft structures generally. It is easy to cause gap between mating surfaces in composite-aluminum assembled structures with the curing deformation of composite. The composite-aluminum, single-lap, single-bolt joints were utilized to investigate the influence of forced assembly, liquid shim and peelable fiberglass shim on the mechanical properties of assembled structures. A steel gasket that removed the middle part was used in the joint to make a gap. The 3D Digital Imagine Correlation (3D-DIC) system was utilized to measure the strain field of specimens and the progressive damage model was created in ABAQUS. The results show that the shim filling can significantly increase the tension stiffness and peak load of the joint compare with forced assembly. As the shim thickness changes, the effects of the liquid shim and the peelable fiberglass shim on the tensile stiffness and peak load shows different. The liquid or peelable fiberglass shim can reduce the strain value around the hole and the peelable fiberglass shim has a better result than liquid shim. The squeeze between the bolt and composite laminate has a greater impact on matrix damage and fiber-matrix shear damage, while the secondary bending has a greater impact on matrix damage and fiber damage.

Progressive damage characteristics of screwed single-lap CFRPI-metal joint subjected to tensile loading at RT and 350°C

This paper outlines progressive damage characteristics of screwed single-lap CFRPI-metal joints subjected to tensile loading at RT (room temperature) and 350°C. Quasi-static tensile tests were performed on screwed single-lap CCF300/AC721-30CrMnSiA joint at RT and 350°C, and the load versus displacement curve, strength and stiffness of joint were gauged and discussed. With due consideration of thermal-mechanical interaction and complex failure mechanism, a modified progressive damage model (PDM) based on the mixed failure criterion was devised to simulate progressive damage characteristics of screwed single-lap CCF300/AC721-30CrMnSiA joint, and simulations correlate well with experiments. By using the PDM, the effects of geometry dimensions on mechanical characteristics of screwed single-lap CCF300/AC721-30CrMnSiA joint were analyzed and discussed.