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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 goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms. [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]

The deep drawing behavior of metal-composite sandwich plates, or fiber-metal laminates, in which aluminum or steel sheets are used as the face layer and composite materials are used as the core layer, is discussed in this work to find the workpieces without fractures and wrinkles. Two types of aluminum, 1050 and 6061, are considered their suitability as face sheets. The preheat effect of aluminum 6061 on formability is also investigated. When steel sheets are used, the effect of blank-holder pressure is included. In addition, to understand the deformation of fabric composite, pure composite laminates are deep drawn. The results of composite laminates show that after drawing, the weft and warp lines are shorter than the other radial lines, causing the specific deformed shape and the variation of the fiber intersection angle. For Al-composite sandwich plates, fractures and wrinkles are easy to occur. Even though the fracture and wrinkle conditions are released with the increase in preheating temperature of aluminum 6061, it may be not enough. For the deep drawing of the steel-composite sandwich plates, in which fractures are avoided, the increase of blank-holder pressure could reduce the wrinkle number. Hence, good quality workpieces without fracture and wrinkle could be obtained when the blank-holder pressure is high enough. [ABSTRACT FROM AUTHOR]

The effects of processing parameters on fatigue lives of graphene oxide papers (GOP) and reduced GOP (RGOP) are investigated. The fabrication method could be either vacuum filtration or pressure filtration, and the important processing parameters include graphene weight fraction in suspension, sonication time for suspension and pressure value for pressure filtration. Fatigue performance of the papers are studied by strain‐controlled fatigue test. Under vacuum filtration method, fatigue lives of both GOP and RGOP decrease with increasing graphene weight fraction. The longest fatigue life is 403 284 cycles for the GOP under highest power sonication time and lowest graphene weight fraction. Fatigue lives of most GOP increase with increasing sonication time up to medium level. Under pressure filtration method, all GOP have shorter fatigue lives than those by vacuum filtration. Scanning electron microscopy is employed to carefully analyse the failed papers in order to clarify the fatigue failure mechanism. [ABSTRACT FROM AUTHOR]

The mixing situation of Fe or Co atoms implanting onto Cu(001) substrate is investigated with regard to substrate temperature and deposition rate by molecular dynamics. The tight-binding-second-momentum-approach many-body potential is used to model the atomic interaction. The results indicate that the morphology of the layer is under epitaxial growth as the substrate temperature is 700 or 1000 K, while it is not epitaxial at the substrate temperature of 300 or 450 K. The quality of epitaxial film is better when the substrate temperature is increased. The intermixing at the deposited layers becomes clear as the substrate temperature increases. It also indicates that there are more Co atoms penetrating into the substrate than the Fe atoms, regardless of the substrate temperature. Hence, one could say that the interface mixing of Co and Cu atoms is better than that of Fe and Cu atoms. When the deposition rate is raised from 5 to 10 atoms/ps, there is no increase in the interface mixing at both systems except for that at low substrate temperature. Furthermore, the first peak of the radial distribution function becomes lower and wider for both the Fe–Cu and Co–Cu systems as the substrate temperature is increasing from 300 to 1000 K. [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]

For damage detection, a hybrid technique consisting of two strategies is proposed. First, grey relation analysis is used to exclude the impossible damage locations such that the number of design variables can be reduced. By using two simple rules proposed in this work, all actual damage locations are included as possible damage locations and the number of design variables is effectively reduced. Secondly, a real-parameter genetic algorithm is combined with simulated annealing and adaptive mechanisms for finding the actual damages. The proposed hybrid algorithm uses only vertical nodal displacements of static responses. In addition to the ideal error-free case in which there is no difference between the experimental data and the theoretical data, the case with 5% error, in which the experimental data is simulated by adding 5% error maximum to the corresponding theoretical data, is considered for measuring error and modeling error. From the results, it is demonstrated that the proposed technique is efficient in damage identification. For the error-free case, the predicted results agree with the true solutions exactly. For the case with 5% error, the prediction obtained is also reasonable. [Copyright &y& Elsevier]

Abstract: An effective algorithm, which combined an adaptive real-parameter genetic algorithm with simulated annealing, is proposed to detect damage occurrence in beam-type structures. The proposed algorithm uses the displacements of static response and natural frequencies of modal analysis, which are obtained by finite element software ANSYS. There are three different kinds of beam structures to verify the performance of the proposed algorithm. These three cases have different boundary conditions and different damage scenarios. From the results, it is demonstrated that the proposed algorithm is efficient in flexural stiffness damage identification for beam-type structures under free of noise condition. Even under the case of noise, the results show that the searched solutions are still in reasonable precision. [Copyright &y& Elsevier]

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]

The purpose of this work is to study the buckling loads, buckling modes, postbuckling behavior, and critical loads of delamination growth for delaminated unidirectional carbon/epoxy composites. Nonlinear buckling analysis, which is a finite-element method including contact elements to prevent the overlapping situation, was applied to predict the delamination buckling loads. In order to predict the delamination growth loads, the total strain-energy release rate criterion, the strain-energy release rate component criterion, and the inerlaminar stress criterion were used in the postbuckling analysis. Experimental results were also provided to compare with the prediction. The results indicate that nonlinear buckling analysis has very good agreement on the buckling loads with the experiments except for the global buckling case. For global buckling mode, the buckling loads are suggested to represent the failure loads of delaminated composites, and postbuckling analysis may not be necessary. For mixed and local buckling modes, the postbuckling behavior is in the mixed mode, and the failure of the delaminated composite is due to the growth of delamination. The errors of the three different criteria in predicting delamination growth loads are from 10% to 22% for different cases. [ABSTRACT FROM PUBLISHER]

The idea of fiber commingling is proposed to increase compressive strengths and the effect of fiber commingling is evaluated by considering two different failure models, buckling failure and shear failure. Micro-buckling failure theory is extended to account for the nonlinear effects of the fiber and matrix by using Ramberg-Osgood stress-strain relations and the tangential modulus concept. In the case of shear failure, a more appropriate method to estimate the shear strength of each component is proposed. The effect of fiber commingling can be estimated from the controlling mode. [ABSTRACT FROM PUBLISHER]