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The quality of woven carbon fiber fabric/polycarbonate thermoplastic composites after thermoforming and demolding was investigated using finite element simulation and the Taguchi orthogonal array. The simulation utilized a discrete approach with a micro-mechanical model to describe the deformation of woven carbon fabric, combined with a resin model. This simulation was validated with bias extension tests at five temperatures. The thermoforming process parameters considered were blank temperature, mold temperature, and blank holding pressure, with three levels for each factor. Optimal values for the fiber-enclosed angle, spring-back angle, mold shape fitness, and the strain of the U-shaped workpiece were desired. The results indicated that the comparison of the stress-displacement curve of bias extension tests verified the application of the discrete finite element method. Results from the Taguchi array indicated that blank holding pressure was the dominant parameter, with the optimal value being 1.18 kPa. Blank temperature was the second most significant factor, effective in the range of 160 °C to 230 °C, while mold temperature had a minor effect. Furthermore, the four quality values are dependent and have a similar trend. The best combination was identified as a blank holding press of 1.18 kPa, a blank temperature of 230 °C, and a mold temperature of 190 °C. [ABSTRACT FROM AUTHOR]

The spring-in behavior of woven carbon fiber/polycarbonate thermoplastic composite is investigated by both the experiment and simulation ways. These thermoplastic composite plates are thermoformed into V-shaped structures, and the final bending angle is measured after demolding. In the finite element simulation to describe the thermoforming and spring-in behavior of the composite, the discrete approach is adopted to simulate the behavior of woven carbon fabric and combined with a resin model. The results from both the experiment and the simulation indicate the spring-in behavior of this thermoplastic composite. For [(±45)]6 blanks, the spring-in angle is around 2.60° for a 60-degree V-shape and around 1.72° for a 90-degree V-shape. For [(0/90)]6 blanks, the spring-in angle is around 2.38° and 1.19° for 60-degree and 90-degree V-shapes, respectively. The [(±45)]6 blank always has a slightly higher spring-in angle than the [(0/90)]6 blank, even though the difference is small. The finite element results show 6% to 12% differences with the experimental values if the spring-in angle is used, and the error is less than 0.6% when the bending angle is compared. By using the present finite element analysis, the results indicate that the stacking sequence could have an evident effect on the spring-in angle, and symmetric laminates have less spring-in effect as compared to their unsymmetric counterparts. [ABSTRACT FROM AUTHOR]

A finite element simulation was utilized in this work to analyze the thermoforming process of woven carbon fiber fabric/polyurethane thermoplastic composite sheets. In the simulation that may be classified as a discrete method, the woven carbon fiber fabric was treated as an undulated fill yarn crossed over an undulated warp yarn, and the resin was considered separately. Then, they were combined to represent the composite sheets. To verify this simulation, bias extension tests under three constant temperatures were executed. After that, the composite was thermoformed into a U-shaped structure and small luggage. From the bias extension tests, the finite element simulation and material properties of the fiber and resin were confirmed. From the comparison of the thermoformed products, the present simulation could provide the deformed profile and fiber-included angles and has good agreement with the experiment. The results also indicate that the stacking sequences of [(0°/90°)]4 and [(+45°/−45°)]4 have quite different product profiles and fiber-included angles. [ABSTRACT FROM AUTHOR]

After manufacturing, fiber-reinforced polymer composite laminates may have residual stresses, resulting in warpage in flat structures and angle changes in angular sections. These shape distortions may cause fitting mismatch problems under high-level assembly, and extra efforts to fix these problems may be needed. The present paper only makes an overview of the angle deviation of angular composite laminates made of either thermoset matrix with autoclave curing or thermoplastic matrix with thermoforming. Depending on the positive or negative angle deviation, spring-back or spring-in behavior is observed. There are many parameters, including intrinsic and extrinsic parameters, that could affect the angle deviation. In the first part of this review paper, experimental results concerning the effects of the part angle, part thickness, lay-up sequence, corner angle, flange size, tool material, tool surface, and cure cycle are summarized. Spring-in angles are generally obtained in this part. In the second part, several prediction methods, such as simple equations and finite element methods, are compared to indicate the considered parameters. Some have good agreement and some have larger errors. The crucial differences may be dependent on the micromechanical theories and the input properties of the composite and the constituents. [ABSTRACT FROM AUTHOR]

An 18-in hybrid wheel consisting of an aluminum alloy disk and a composite rim under 13° impact test is considered in this study. The rim is made of carbon fabric/polyurethane composites fabricated by resin transfer molding. Explicit finite element analysis with progressive failure function is used to investigate the failure situation of the hybrid wheel and the suitable braid angle of the braided composite. The effective elastic constants and strengths of the braided composites predicted by basic finite element analyses are adopted, whereas the true stress-strain curve of aluminum is used for the disk. Simulation results indicate that the aluminum alloy disk is safe after the impact test, whereas the rim is damaged. The volume of failed elements after impact simulation is selected as an indicator to obtain a quantity that can be used to represent the damage situation of the rim. Compared with the test results of a real hybrid wheel with [±30°] fiber angle in the rim, the hybrid wheel with fiber angle in the rim that is greater than [±30°] could pass the impact test. [ABSTRACT FROM AUTHOR]

In the electromagnetic forming (EMF) process, the Lorentz force is generated by the repulsive interaction of magnetic field between a pulse transient current in a coil and an eddy current in a workpiece. During the process, the current will generate Joule heat in both the coil and workpiece raising their temperatures. The objective of this work is to build a coupled analysis to consider the temperature effect during the electromagnetic sheet metal forming process by using a finite element analysis. During the analysis, the electromagnetic, mechanical and temperature problems are considered simultaneously. Then, the coupling effects of the temperature with eddy currents, magnetic fields, magnetic force density, and deflection of the sheet metal are discussed. The results indicate that the temperature increasing is significant especially during repeated working cycles, and the deflection of a sheet metal is reduced as the increasing of the coil temperature. Hence, this temperature effect should be considered to avoid the failing of products and to improve the life of the forming coil, especially in a mass production process. [ABSTRACT FROM AUTHOR]

Nonlinear buckling analysis using the finite element method is employed to study the buckling and postbuckling behavior of unidirectional composite materials with two delaminations under uniaxial compression. Strain energy release rates around the crack tips are calculated to assess the possible growth of the two delaminations in various positions and with different lengths. From the analysis, the results indicate that if the long delamination is close to the surface of the laminate, the inner, short delamination has no effect on the buckling stress. However, the presence of inner, short delamination may significantly change the behavior of delamination growth. If the short delamination is above the long delamination that is located on the middle surface, the presence of the short delamination may significantly reduce the buckling stress. But its effects on the behavior of delamination growth is minor. [Copyright &y& Elsevier]

The buckling and postbuckling behaviors of composite laminates with multiple delaminations under uniaxial compression are experimentally studied. The through-width multiple delaminations with triangular shape are used to simulate impact damage. A nonlinear buckling analysis from finite element method is also used to predict the buckling loads that are compared with experimental results. The critical delamination growth loads of multiple delaminations are obtained from postbuckling tests. The difference of single delamination and multiple delaminations on buckling behavior and postbuckling behavior is discussed. The results indicate that the buckling loads obtained by the nonlinear buckling analysis are in reasonable agreement with the experimental values. Experiments have proven that short delaminations distributed under the near-surface, long delamination have no effects on the buckling loads. The critical delamination growth loads of single-delamination specimens are much higher than those of multiple-delamination specimens, and the shape of the triangular multiple delaminations can affect the critical delamination growth loads. [ABSTRACT FROM PUBLISHER]