This paper reports a novel method for fabrication of an electro-thermal heating element, as de-icer or anti-icer, for the polymer-based composites. The plasma spray technique was utilized for the deposition of a Nickel-Chrome-Aluminum-Yttrium (NiCrAlY) coating layer as a heating-element on top of the glass/epoxy composite. To improve the adhesion strength and deposition efficiency of the coatings and to protect the composite fibers during grit blasting and spraying, a woven wire stainless steel mesh was added to the composite substrates during the composite fabrication process. Metal mesh will act as an anchor to keep the coating on the surface. Two types of woven wire and two types of NiCrAlY powder with the fine and coarse particle size distributions were used. Good processing parameters for grit blasting and plasma spraying are identified. It is found that the surface modification method applied to the composite substrates prior to the coating process makes a significant improvement in the coating thickness uniformity and deposition efficiency. Several tests were conducted on the coated samples for determination of their mechanical and electrical properties. Using flat-wise tensile tests, it is shown that application of proper surface modification method and set of spray parameters could result in improving the coating bonding strength significantly. The electrical and thermal analyses of the coated samples are also performed. It is shown that the coated samples have a high capability in the generation of heat and can be used as a heating-element.

The synergistic effect of combining different modification methods was investigated in this study to improve the interlaminar toughness and delamination resistance of fiber reinforced polymers (FRP). Epoxy-compatible polysulfone (PSU) was end-capped with epoxide group through functionalization, and the fiber surface was chemically grafted with an amino functional group to form a micron-size rough surface. Consequently, the long chain of PSU entangles into cross-linked thermoset epoxy network, additionally, epoxide group on PSU further improves the bonding through chemical connection to the epoxy network and amino group on the fiber surface. The combined modification methods can generate both strong physical and chemical bonding. The feasibility of using this method in vacuum-assisted resin transfer molding was determined by rheometer. The impact of formed chemical bonds on the cross-linking density was examined through glass transition temperatures. The chemical modifications were characterized by Raman spectroscopy to determine the chemical structures. Synergistic effect of the modification was established by mode I and mode II fracture tests, which quantify the improvement on composites delamination resistance and toughness. The mechanism of synergy was explained based on the fracture mode and interaction between the modification methods. Finally, numerical simulation was used to compare samples with and without modifications. The experiment results showed that synergy is achieved at low concentration of modified PSU because the formed chemical bonds compensate the effect of low cross-linking density and interact with the modified fiber.

A low concentrated polystyrene (PS) additive to epoxy is used, since it is able to reduce the curing reaction rate but not at the cost of increasing viscosity and decreasing glass transition temperature of the curing epoxy. The modified epoxy is cocured with a compatible thermoplastic interleaf during the vacuum assisted resin transfer molding (VARTM) to toughen the interlaminar of the composites. Using viscometry, the solubilities of thermoplastics (TPs) polycarbonate (PC), polyetherimide (PEI), and polysulfone (PSU) are determined to predict their compatibility with epoxy. The diffusion and precipitation process between the most compatible polymer PSU and epoxy formed semi-interpenetration networks (semi-IPN). To optimize bonding adhesion, these diffusion and precipitation regions were studied via optical microscopy under curing temperatures from 25 °C to 120 °C and PS additive concentrations to epoxy of 0–5%. Uniaxial tensile tests were performed to quantify the effects of diffusion and precipitation regions on composite delamination resistance and toughness. Crack paths were observed to characterize crack propagation and arrest mechanism. Fracture surfaces were examined by scanning electron microscopy (SEM) to characterize the toughening mechanism of the thermoplastic interleaf reinforcements. The chemically etched interface between diffusion and precipitation regions showed semi-IPN morphology at different curing temperatures. Results revealed deeper diffusion and precipitation regions increase energy required to break semi-IPN for crack propagation resulting in crack arrests and improved toughness.

Various methods of toughening the bonding between the interleaf and laminate glass fiber reinforced polymer (GFRP) have been developed due to the increasing applications in industries. A polystyrene (PS) additive modified epoxy is used to improve the diffusion and precipitation region between polysulfone (PSU) interleaf and epoxy due to its influence on the curing kinetics without changing glass transition temperature and viscosity of the curing epoxy. The temperature-dependent diffusivities of epoxy, amine hardener, and PSU are determined by using attenuated total reflection–Fourier transfer infrared spectroscopy (ATR–FTIR) through monitoring the changing absorbance of their characteristic peaks. Effects of PS additive on diffusivity in the epoxy system are investigated by comparing the diffusivity between nonmodified and PS modified epoxy. The consumption rate of the epoxide group in the curing epoxy reveals the curing reaction rate, and the influence of PS additive on the curing kinetics is also studied by determining the degree of curing with time. A diffusivity model coupled with curing kinetics is applied to simulate the diffusion and precipitation process between PSU and curing epoxy. The effect of geometry factor is considered to simulate the diffusion and precipitation process with and without the existence of fibers. The simulation results show the diffusion and precipitation depths which match those observed in the experiments.

The objective of this research is to study the effect of graphene platelet (GPL) loading on the machinability of epoxy-based GPL composites. To this end, micro-milling experiments are conducted on composites with varying GPL content and their results are contrasted against that of plain epoxy. The material microstructure is characterized using transmission electron microscopy and scanning electron microscopy methods. Chip morphology, cutting force, machined surface morphology, and tool wear, are employed as the machinability measures for comparative purposes. At lower loadings of GPL (0.1% and 0.2% by weight), the deformation of the polymer phase plays a major role; whereas, at a higher loading of 0.3% by weight, the GPL agglomerates and interface-dominated failure dictates the machining response. The minimum chip thickness value of the composites decreases with an increase in GPL loading. Overall, the 0.2% GPL composite has the highest cutting force and the lowest tool wear.

A multiphase finite element model using the commercial finite element package ABAQUS/EXPLICIT is developed for simulating the orthogonal machining of unidirectional fiber reinforced composite materials. The composite materials considered for this study are a glass fiber reinforced epoxy and a tube formed carbon fiber reinforced epoxy. The effects of varying the fiber orientation angle and tool rake angle on the cutting force and damage during machining are considered for the glass fiber reinforced epoxy. In the case of carbon fiber reinforced epoxy, only the effect of fiber orientation on the measured cutting force and damage during machining is considered. Two major damage phenomena are predicted: debonding at the fiber-matrix interface and fiber pullout. In the multiphase approach, the fiber and matrix are modeled as continuum elements with isotropic properties separated by an interfacial layer, while the tool is modeled as a rigid body. The cohesive zone modeling approach is used for the interfacial layer to simulate the extent of debonding below the work surface. Bulk deformation and shear failure are considered in the matrix for both the models and the glass fiber. A brittle failure criterion is used for the carbon fiber specimen and is coded in FORTRAN as a user defined material (VUMAT). The brittle failure of the carbon fibers is modeled using the Marigo model for brittle failure. For validation purposes, simulation results of the multiphase approach are compared with experimental measurements of the cutting force and damage. The model is successful in predicting cutting forces and damage at the front and rear faces with respect to the fiber orientation. A successful prediction of fiber pullout is also demonstrated in this paper.

The most common method currently employed in industry to trim composites is machining either with conventional fluted cutters or with diamond abrasive cutters. Although diamond abrasive machining is a common method for trimming composites, there is no research literature which addresses the use of this type of cutter. As a result, an experimental investigation was undertaken to establish the characteristics of the machined edges produced by diamond abrasive cutters in graphite/epoxy laminates. In addition, preliminary tests were performed to document the cutter forces produced by representative cutters with various grit sizes and feed rates. The machined edges produced were generally found to be free of delamination and characterized by regular grooving produced by the diamond grains. The surface finish was found to be inversely proportional to the grit number and was not affected by feed rate or cutting mode. Cutter forces were generally found to increase with material removal rate and the average side load was generally about 60 percent of the thrust forces.

Rapid prototyping (RP) technologies are valuable for reducing product development cycle times by creating physical models for visual inspection and form-fit studies directly from a 3-D database. However, if the part is meant for volume production, tooling will be necessary. Tool development and fabrication using conventional techniques and materials is time consuming and expensive. Therefore, it is risky to commit to production tooling in the initial stages of product development. Low volume prototyping is highly desirable but requires a small number of parts (hundreds) to be produced quickly and economically. To meet this need, this paper studies direct tooling using the RP technology of stereolithography (SL) to produce photopolymer tools. Without modifications to improve thermal response, SL molds will not be able to produce production-quality parts. This experimental study quantifies the thermal characteristics of an SL mold for a simple part geometry. Several modifications that affect thermal properties are then studied and both thermal response and part quality are quantified. The data indicate that although it is possible to change the thermal response of an SL mold and obtain reasonable parts, the ability to duplicate traditional mold characteristics (and thus simulate part production before committing to high-volume tooling) is probably not practical. Similar results were achieved when using a more realistic final-part geometry on a production mold machine. Although mold process simulation using SL molds could provide useful design guidance for traditional high-volume part production, this work suggests that these SL molds can be used for low-volume part production. By reducing mold fabrication time and costs, low-volume part production could become cost-effective using traditional high-volume manufacturing techniques. [S1087-1357(00)00702-4]

Composite materials are ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are required. Currently, linear cutting of composite materials has been increasingly practiced in industry and milling will be an important technology for wider applications of the materials and the benefit of onestation operation integrating linear and surface machining. Abrasive waterjet is adequate for machining of composite materials thanks to minimum thermal or mechanical stresses induced. The present paper discusses the feasibility of milling of composite materials by abrasive waterjet; it studies the basic mechanism of chip formation, single-pass milling, double-pass milling followed by the repeatable surface generation by multiple-pass milling. The mechanisms of material removal-deformation wear and cutting wear are studied first. High volume removal rate as well as a neat surface are desired. The major parameters affecting material removal rate are hydraulic pressure, standoff distance, traverse rate and abrasive flow rate. Dimensional analysis shows these significant parameters in machining and the results are compared with the theory of material erosion. The single-pass milling tests of carbon/epoxy are then conducted. The milling characteristics determining the generation of an extended surface are depth, width and width-to-depth ratio. The following dimensional analysis constructs the correlation between parameters and the surface characteristics. Based on the results of single-pass milling tests, the paper discusses the double-pass milling specifically considering the effect of lateral feed increments. The study then extends to six-pass milling. The obtained surface roughness from the sixpass milling is expressed as a function of the width-to-depth ratio and the lateral increment. With the knowledge of the volume removal rate and the surface roughness as well as the effects of the major process parameters, one can proceed to design a milling operation by abrasive waterjet.

Fiber reinforced composites, though relatively new, have already become important engineering materials. So far the main emphasis of research has been on the development of materials, but nowadays more attention is being paid to the industrial manufacture of products made of composites. Conventional machining methods and some unconventional machining methods like laser beam machining (LBM) and water jet machining (WJM) cannot be effectively applied for machining of composites due to the resulting problems of air borne dust, tool wear, and thermal damage. Recently electrochemical spark machining (ECSM) has been applied for the cutting and drilling of holes in composites. The success achieved in the application of ECSM for cutting of composites has stimulated interest in exploring the prospects of use of traveling wire electrochemical spark machining (TW-ECSM) process for cutting of composites. An apparatus for TW-ECSM is designed and fabricated in the laboratory. The results about the feasibility of the process and its performance during machining of composites are presented in this paper. Experiments are carried out on glass-epoxy and kevlar-epoxy composites, using sodium hydroxide (NaOH) as electrolyte. The wire and the workpiece were kept in physical contact with each other by the use of a gravity feed mechanism. The effects of voltage and concentration of the electrolyte on material removal rate, average diametral overcut, tool wear rate, and wire erosion ratio are reported. The theoretical analysis of the mechanism of the process identifies the thermo-mechanical phenomena as the main source of material removal in ECSM.

Delamination is the major concern during drilling of composite laminates. Delamination, in addition to reducing the structural integrity of the laminate, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Drilling-induced delamination occurs both at the entrance and at the exit planes. This paper presents an analysis of delamination during drilling. The analysis uses a fracture mechanics approach in which the opening-mode delamination fracture toughness, a material parameter, is used with a plate model of the laminate. The analysis predicts an optimal thrust force (defined as the minimum force above which delamination is initiated) as a function of drilled hole depth. Good agreement is achieved with data obtained from drilling carbon fiber-epoxy laminates. An advantage of the model is that it can predict varying degrees of delamination for other materials, such as glass fiber-epoxy, and for hybrid composites. In addition, the optimal thrust force for no delamination can be used to control a drilling machine with thrust force feedback for maximizing productivity.

Reports have indicated the poor performance of the conventional type of cutting tools during machining of composites. In this paper electrochemical spark machining (ECSM) for the cutting and drilling of holes in the composites is being proposed. The feasibility of using ECSM for composites was first ascertained. Then, kevlar-fiber-epoxy and glass-fiber-epoxy composites as work material, copper as tool material, and an aqueous solution of NaCl as electrolyte were used. It has been concluded that the ECSM is a viable solution for cutting of Fiber Reinforced Plastics (FRP). For achieving desired accuracy, surface finish, and economics of the process, the machining parameters should be optimized.

In this research, a statically-balanced direct-drive manipulator is designed and constructed to achieve improved dynamic behavior for compliance control [10, 11, 12]. The manipulator mechanism, incorporating a four-bar linkage, is designed so that its functional parts are balanced in all positions without the addition of counterweights. The motors are never loaded by gravity. As a result, smaller motors with less torque can be used to achieve higher speed, accuracy, and repeatability in fine manipulation tasks. The robot is powered by high-torque AC synchronous motors. The mechanism is comprised of graphite-epoxy and AA7075T6 aluminum materials. The manipulator is controlled by a parallel processor computer.

Several closed-form solutions exit to predict elastic constants of a composite material. Most of these methods give comparable results for epoxy matrix composites, but not for flexible matrix composites, where the matrix is much softer than the fiber. We have devised a method that uses energy values given by finite element analyses of composite models, subjected to various independent displacement conditions. Results for flexible matrix composites thus obtained are compared with those determined by some of the existing methods. Closed-form solutions are recommended for approximate prediction of the different elastic constants by this comparison.

A case study of curing deformations in square struts laminated from unidirectional prepreg is presented that uses laminate and three-dimensional finite element analyses to analyze critical shrinkage behavior. The manufacture of square graphite epoxy struts is complicated by twisting deformations during cooling from autoclave cure temperatures that are not predicted by laminate analyses. Three-dimensional finite element analyses are presented that correctly predict the twisting but not its amplitude which appears to be dependent on a geometric nonlinearity. The three-dimensional and laminate results both show large self equilibriating stresses in individual plies caused by local shrinkage and stiffness property differences. This is a key finding that identified the source of shape instability and confirmed design changes to minimize twisting deformations that were first determined experimentally.

Uncertain eigenvalue problem of linear vibration is analyzed by means of the stochastic finite element method, the basis of which utilizes mean-centered second order perturbation technique. Attention is paid to the fluctuation of the stacking sequence, that is, fiber orientation and layer thickness of FRP laminated plates. The stacking sequence is expressed in terms of probabilistic variables. The eigenvalue problem is formulated based on the Kirchhoff-Love’s theory of thin plate, the stretching, coupled and bending stiffnesses of which are uncertain due to the stacking sequence. The numerical analyses deal with the vibration of simply-supported graphite/epoxy plates. The sensitivity of the input stacking sequence and the correlation coefficients of the probabilistic variables are evaluated quantitatively.

A study of process-induced stresses in advanced fiber-reinforced composite laminates is presented. An analysis of the residual thermal stresses is conducted on the basis of laminate thermoelasticity theory in conjunction with a quasi-three-dimensional finite element method. Formulation of the numerical method is briefly outlined in the paper. To illustrate the fundamental nature of the problem, numerical examples for a quasi-isotropic [0 deg/90 deg/ ± 45 deg] s graphite-epoxy composite system are presented. Complex three-dimensional stress states of significant magnitude are reported. Emphasis is placed on the interlaminar stress distributions along ply interfaces. Effects of laminate stacking sequence on the residual thermal stresses are examined in detail. Implications of the results on deformation and failure of composite laminates are discussed.

A theoretical solution for the response of a viscoelastic beam to off-center low speed transverse impact is presented. The flexural model adopted for investigation consists of a uniform Bernoulli-Euler beam whose behavior has been generalized to include a linear viscoelastic constitutive relation for each element of the beam. Further, the beam and rigid impactor are assumed to remain in contact during the resulting motion and a consistent set of initial displacement and velocity distributions is adopted for the beam. The solution method utilizes two Laplace transforms, i.e., one with respect to space and the other with respect to time. Comparison of the numerical predictions of the theoretical model with central impact test results on graphite-epoxy composite laminates indicates a good agreement between theory and experiment.

The present paper is devoted to the study of the influence of flank wear upon the contact and internal stresses in a single-point tool. A comprehensive model for the distribution of contact stresses along the wear land is proposed and compared with experimental results obtained from photoelastic investigations. For this purpose orthogonal machining of lead was carried out at low speed and constant depth of cut, making use of a transparent epoxy tool provided with a pre-honed wear flat along the flank surface. Wear level and rake angle seem to have influence on both the tool-chip and tool-work contact stresses in differing degrees. The elastic stress field in the tool wedge is evaluated analytically for given mixed boundary loading conditions. These results, on comparison with the experimental data obtained from photoelastic investigation and actual cutting test, indicate noticeable influence of wear level upon contact stress redistribution and stress field reorientation. Based on this, the role of flank wear upon the brittle strength of the tool is clarified.

A general forced-vibration analysis is presented for laminated anisotropic rectangular plates including material damping. The theory used is the laminated version of the Mindlin plate theory and includes thickness-shear flexibility and rotatory and coupling inertia. Solution is obtained by the Rayleigh-Ritz method, extended to include the energy dissipated and the work done by the excitation. The analysis is applied to prediction of the resonant frequencies and associated nodal patterns and damping ratios of the first five modes for a series of rectangular plates with free edges. The plates considered consist of unidirectional boron-fiber/epoxy composite material with respective fiber orientations of 0, 10, 30, 45, 60, and 90 deg. Using ply stiffness and damping properties obtained from micromechanics analyses and constituent-material experimental properties, the agreement with the corresponding experimental results reported in the literature are excellent.