Papers by Keyword: CFRP Laminate

Abstract: Carbon fibre composites used in many safety-critical applications experience damage due to operating environment such as bird strike, hailstorm etc., In some cases, the damage is barely visible and its presence in the structure can cause accelerated damage leading to catastrophic failure. In this paper, the results of fatigue damage progression in woven CFRP laminate subjected to constant amplitude loading for un-impacted specimens as well as impacted specimens are presented. The stiffness of the specimens was periodically monitored during fatigue testing to arrive at the rate of damage progression. Special experiments were carried out under a programmed version of an equivalent fighter aircraft loading – FALSTAFF (Fighter Aircraft Loading Standard for Fatigue and Fracture) and it was observed that the damage progression is slower in case of spectrum loading compared to constant amplitude loading. The effect of load sequencing on damage is investigated in this paper.

Abstract: The effects of thickness and impact energy on the medium leakage of composite laminates were discussed in this paper. Impact tests for the composite laminates with the size of 600 mm×700 mm with three different thicknesses were subjected to impact energy levels from 5 J to 40 J. The medium leakage and the damaged area were investigated according to different energy levels and stacking sequences. The damage area was evaluated by visual inspection and three-dimensional microscope. The experimental results reveal that the impact damage of CFRP laminates with three different thicknesses tends to be more severe as impact energy increases. The impact area and the crater depth increases with increasing impact energy. The impact area and the crater depth decreases with increasing thickness for the same impact energy.

Abstract: Various kinds of damage may occur during the drilling of carbon fiber reinforced polymer composite (CFRP). To review the mechanism of CFRP drilling, a three-dimensional macro-mechanical finite element (FE) model was constructed for CFRP drilling based on FE software tool Abaqus. The workpiece was modeled as equivalent homogenous anisotropic material (EHAM) with elastic-failure behavior. Three-dimensional Hashin criterion was used to predict the material failure. The material was implemented in user subroutine VUMAT. The drilling process was analyzed and the thrust force with respect to cutting conditions was evaluated. The simulation shows that thrust force increase with feed rates while decrease with spindle speed, as agrees with experiment.

Abstract: The preexisting strains of structures have some influence on the efficiency of CFRP Laminate. Based on the analysis of the abundant existing research productions, the calculation formulas of CFRP Laminate are proposed based on the supposition of plane section and balance of forces considering the preexisting strain. And the formulas are easy to understand and master for designers. By discussing the relation between the preexisting strain and relative depth of compression area, the essentials of the impact on reinforcement effect of residual strain are confirmed. The results can offer reference bases for strengthening engineering design with CFRP.

Abstract: In this study, distributions of microscopic stress at free edges of unidirectional carbon fiber-reinforced plastic laminates (CFRP laminates) are analyzed three-dimensionally, based on a homogenization theory for time-dependent composites. For this, the homogenization theory is reconstructed for free edge problems using a traction-free boundary condition. Then, an analysis domain is reduced using the point-symmetry of the internal structure of the unidirectional CFRP laminate. Moreover, the substructure method is newly introduced into the theory to reduce the computational costs required for the analysis. The present method is then applied to the elastic-viscoplastic microscopic stress analysis at free edges of unidirectional carbon fiber/epoxy laminates subjected to an in-plane uniaxial tensile load. It is shown that complex microscopic stress distributions occur in the vicinity of the free edge, especially around fiber/matrix interface regions.

Abstract: A two-dimensional macro-mechanical finite element (FE) model is developed to study the orthogonal cutting process of CFRP unidirectional laminate by the finite element software ABAQUS. The CFRP laminate is defined as an equivalent orthotropic, homogeneous single-phase material. On the basis of composite unidirectional laminate plane stress-strain and strength theory, the author adopts Hashin progressive damage criteria in the FE model. Based on the results of finite element simulation, the changes of cutting force in the chip formation process of CFRP laminate are analyzed, the Hashin damage in the cutting process and the influences of fiber orientation on cutting force, chip formation mechanism and sub-surface damage are explored as well. The comparison between this paper and previous related research shows that the results have a reasonable agreement with the previous achievements.

Abstract: This article focuses on the drilling of carbon fiber reinforced plastics (CFRP) laminate with brazed diamond core drill under no cooling condition. The effect of grit size, wall thickness of core drill and feed speed on machining quality at the hole exit is studied. The experimental results indicate that the grit size has a significant influence on the diameter of the hole exit. The expanding factor of diameter at hole exit increases with the decrease of grit size. Both large wall thickness and high feed speed lead to serious drilling-induced defects of the hole exit. The drilling-induced defects at hole exit are transformed from broken-edge and burr to local tear.

Abstract: This study is mainly about the drilling of carbon-epoxy laminates. Variation of cutting parameter such as feed rate (50,100 and 150 mm/min) and speed(400,800,1200 rpm) were tested in this study. 6 different laminates orientation (0°/0°/0°/0°, 45°/45°/45°/45°, 0°/45°/0°/45°, 45°/0°/45°/0°, 0°/0°/45°/45° and 45°/45°/0°/0°) were tested in order to see which one is the best. HSS twist drill with 4mm diameter was use in this study. The damage of the composites was seen under digital microscope. The aim of this study is to find the minimum force and the minimum damage mechanism i.e.: entry and exit delamination. The drilling process with different parameter of cutting and the orientation were carried out in order to see the influenced of this parameter to the force and the damage mechanism. The general factorial was used to randomise the number of experiment.

Abstract: In this study, carbon fiber reinforced polymer (CFRP) laminates that were under three-point bending load within and without initial impact damage, were detected and monitored by ultrasonic C-scan method. The defect morphology at various load levels was recorded. The dynamic monitoring for the growth of delaminations in CFRP laminates was acquired, and it provided an experimental evidence for the health monitoring on CFRP in service.

Abstract: In this paper, experimental study is carried out to evaluate the flexural performance of reinforced concrete beams strengthened with different ratios of carbon fibre reinforced polymer (CFRP) laminates. Four rectangular reinforced concrete beams strengthened with different reinforcement ratios of CFRP laminates are tested to failure under transverse bending on a simply supported span of 1.9 m. The increase of ultimate strength provided by the bonded carbon fiber is assessed and failure mode is identified. The results indicated that the flexural capacity of beam was significantly improved as the layers of laminates increased. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened beams. However, de-bonding of CFRP laminates from the concrete surface is still a concern for the case of multi-layer strengthening of beam. Based on the observed results, recommendations are made to prevent the premature de-bonding failure of strengthened beams.