Thermoplastic Composite Sheet Research Articles

Development of the forming limit diagram for fiber-reinforced thermoplastic composites and its temperature effect

The aim of this study is to investigate the formability properties of thermoplastic composite sheets and to develop a forming limit diagram (FLD) for them under ambient and elevated temperatures. Polypropylene thermoplastic composite sheets reinforced with unidirectional continuous glass fibers in a four-layer 0–90 layup were used in this research. Experimental findings demonstrate that the failure of samples at room temperature is more similar to brittle failure and occurs suddenly, whereas at elevated temperatures, the failure resembles ductile failure and occurs gradually. Employing the Nakajima method, a forming limit diagram for the composite material was successfully established at both ambient and elevated temperatures. The resultant forming limit diagrams illustrate an augmented strain tolerance of the material at elevated temperatures. Notably, despite the increased depth of stretch observed at elevated temperatures in comparison to ambient conditions, a concomitant reduction in the force requisite to induce deformation is evident.

Thermoforming Simulation of Woven Carbon Fiber Fabric/Polyurethane Composite Materials

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.

Development and Characterization of Sugar Palm (Arenga Pinnata (Wurmb. Merr)) Fiber Reinforced Cassava (Manihot esculenta) Starch Biopolymer Composites

ABSTRACT The study aims to develop a biopolymer composite made of sugar palm fiber and cassava starch that may degrade over time and to investigate the physical and structural characteristics of biocomposite films. Sugar palm fiber (SPF) was cast into a biocomposite with cassava starch (CS) as the matrix and fructose as the plasticizer using the casting process. The thermoplastic CS composite sheet was loaded with different amounts of SPF (0%, 5%, 10%, 15%, and 20% dry starch). The addition of SPF considerably improved the physical and thermal properties. It enhanced the thickness of the material while lowering its density, water content, and biodegradability. However, there was no significant increase in the tensile properties of the composite films. The filler had been absorbed into the matrix, according to SEM micrographs. With a higher concentration of SPF, the SPF/CS films had a more heterogeneous surface. It is indeed possible that the addition of SPF changed the film characteristics of cassava starch, potentially compromising the performance of the films. Overall, the findings of this study concentrate on enlightening about biopolymer composite film and highlighting its great potential for the food packaging market.

Investigation of the spring-back phenomenon in two-dimensional bending of continuous glass fiber-reinforced polyamide composite sheets

Thermoplastic composite sheets have great potential for use in industrial applications owing to their fast-forming properties in the mold. One of the important matters of forming is the tendency of the part to recover elastically after it comes out of the mold. This behavior affects the dimensional accuracy of the final part. In this study, V-bending experiments were carried out to understand the spring-back phenomenon of continuous glass fiber-reinforced polyamide-6 composite sheets. Unidirectional and cross-ply composite sheets were used in the experiments and bending angle, die radius, pressure, and dwell-time were investigated systematically. After bending, the spring-back angles of the parts were measured and the effects of the inspected parameters were compared. Also, variations in part thickness caused by spring-back were evaluated. Finally, the deformations in the specimens resulting from the residual stress were visualized with a scanning electron microscope. When the results were compared, it was determined that the bending conditions where the spring-back defect could be minimized were 6 mm radius, 90° angle, 120 s dwell-time, and 3 MPa pressure. Under these situations and in sheets bent 90°, the amount of spring-back was determined as 22° for unidirectional composites and 15° for cross-ply composites.

Warmforming Flow Pressing Characteristics of Continuous Fibre Reinforced Thermoplastic Composites.

The paper presents research regarding a thermally supported multi-material clinching process (hotclinching) for metal and thermoplastic composite (TPC) sheets: an experimental approach to investigate the flow pressing phenomena during joining. Therefore, an experimental setup is developed to compress the TPC-specimens in out-of-plane direction with different initial TPC thicknesses and varying temperature levels. The deformed specimens are analyzed with computed tomography to investigate the resultant inner material structure at different compaction levels. The results are compared in terms of force-compaction-curves and occurring phenomena during compaction. The change of the material structure is characterized by sliding phenomena and crack initiation and growth.

Enhanced Simulation of Infrared Heating of Thermoplastic Composites Prior to Forming under Consideration of Anisotropic Thermal Conductivity and Deconsolidation by Means of Novel Physical Material Models.

In recent years, thermoplastic composites have found their place in large business sectors and are in direct rivalry to thermoset matrix composites. In order to ensure efficient and lean processes, process modeling gains ever-growing attention. This work shows the computational fluid dynamics (CFD)-modeling of a typical heating step in a thermoforming process of a thermoplastic composite sheet. When heating thermoplastic composites, the heat conduction proceeds anisotropic, and the sheets are subject to thermal deconsolidation when heated above the melting temperature of the polymer matrix adding to the anisotropic effect. These effects are neglected in known process models and this study shows the first successful attempt at introducing them into CFD-modeling of the heating of thermoplastic composite sheets. Thus, the simulation requires temperature dependent values for the anisotropic thermal conductivity and the coefficient of linear thermal expansion, which are calculated with novel physical models which were developed solely for this cause. This alters the behavior of an isotropic CFD-model and allows the successful validation via laboratory experiments using glass fiber reinforced polypropylene (PP/GF) sheets with embedded thermocouples to check the internal temperature distribution when the sheet is heated to the designated forming temperature in a composite thermoforming press. The incorporation of this newly developed process model reduces the error in the core temperature prediction from close to 70 °C to 3 °C at the forming temperature.

Effects of gripper location and blank geometry on the thermoforming of a carbon-fiber woven-fabric/polyphenylene sulfide composite sheet

The effects of gripper location and blank geometry on the thermoforming of a pre-consolidated carbon-fiber woven-fabric/polyphenylene sulfide (PPS) thermoplastic composite sheet (deformed into a U-beam geometry) are investigated both experimentally and numerically. The thermoforming experiments and simulations are performed at constant tool (160oC) and sheet (315oC) temperatures by using four thermoplastic composite blanks, which are different in geometry and inserted into the blank holder using gripping springs. Thermocouples are inserted on the composite sheet and forming molds in order to monitor the temperature variations during thermoforming. Thermoforming process is simulated in Ls-Dyna; the composite sheet is modeled using the Anisotropic Hyperelastic Material Model (MAT_249). An optimum punch speed and a spring constant are initially determined through numerical simulations. Afterward, the numerical thermoforming processes of four different blanks are implemented separately. Results reveal that the simulations show good agreements with the experiments in terms of defects formation and the maximum shear angles between the fiber directions on the final thermoformed U-beam geometry. When the blank is attached with eight springs from the lugs to the blank holder, the deformation and distortion of the net edge of the sheet are avoided, resulting in significant reductions in the extent of defect formation.

Investigation of dynamic properties of a three-dimensional printed thermoplastic composite beam containing controllable core under non-uniform magnetic fields

This paper presents the dynamic responses of sandwich beams with 3D printed thermoplastic composite face sheets and multi-walled carbon nanotubes reinforced magnetorheological elastomer (MWCNT-MR elastomer) cores under non-uniform magnetic fields. A higher-order beam theory (HoBT) is employed to express the beam‘s displacement field. The governing equations of the 3D printed thermoplastic sandwich beam are derived using Lagrange‘s principle and discretized by the finite element method. The validity of the present method is confirmed through comparison with the results available in the literature. The stiffness and damping characteristics of the 3D printed thermoplastic sandwich beam are investigated in relation to support conditions, non-homogeneous magnetic flux, and core-face sheet thickness ratio.

Investigating the Effects of Forming Parameters on Molding Force and Springback in Deep Drawing Process of Thermoplastic Composite Laminates

The automotive industry and research centers have intensified the search for innovative solutions in the field of material technologies and have recently accelerated their work on thermoplastic based composites in line with their requirements. Thermoform method is used for rapid forming of thermoplastics and composites. In this process, mold design and especially molding parameters are important for part quality. Thermoplastic composite sheets take the shape of their final form by spring back after they come out of the mold as in sheet metals. Therefore, springback is a parameter that should be taken into account in the manufacturing process and product design. In this study, preliminary research was carried out to design the forming process in thermoform mold. The experiments were done on Nakajima test setup and according to ISO 12004 standard. In the deep drawing of thermoplastic composite laminates, the effects of different holding pressure (0.4; 0.6; 0.8 MPa), punch speed (90, 120, 150 mm/min), specimen temperature (129, 159, 169 oC) and piece depth (20, 25, 30 mm) parameters on the molding force were examined and the spring back amount of deep drawn specimens was determined. As a result of the experiments, as the specimen temperature increased the molding force decreased. The molding force increased as the holding pressure increased. Increasing punch speed caused an increase in required molding force. As a result of the experiments, it was concluded that deep drawing can be made up to a depth of 25 mm.

Enhanced Infrared Heating of Thermoplastic Composite Sheets for Thermoforming Processes

Abstract Thermoforming of thermoplastic composites attracts increasing attention in the community due to the mechanical performance of these materials and their recyclability. Yet there are still difficulties concerning the uniformity of the heating and overheating of parts prior to forming. The need for higher energy efficiencies opens new opportunities for research in this field. This is why this study presents a novel experimental method to classify the efficiency of infrared heaters in combination with different thermoplastic composite materials. In order to evaluate this, different organic sheets are heated in a laboratory scale heating station until a steady state condition is reached. This station mimics the heating stage of an industrial composite thermoforming device and allows sheets to slide on top of the pre-heated radiator at a known distance. By applying thermodynamic balances, the efficiency of chosen parameters and setups is tested. The tests show that long heating times are required and the efficiency of the heating is low. Furthermore, the efficiency is strongly dependent on the distance of the heater to the sheet, the heater temperature and also the number of heating elements. Yet, using a full reflector system proves to have a huge effect and the heating time can be decreased by almost 50%.

Finite-element analysis of EPP foam core/self-reinforced PP sandwich structures

In this study, fully recyclable and elastic–plastic deformable sandwich panels were developed by considering the mass production requirements, as well as the lightweighting needs of the automotive industry. Expanded polypropylene (EPP) foam core and self-reinforced polypropylene (PP) thermoplastic composite face sheets were selected to produce sandwich panels. Three-point bending experiments were performed to obtain the flexural behavior of the sandwich panels. Finite-element analysis (FEA) of the sandwich beams was carried out and confirmed by experimental results. Three different EPP foam cores with densities of 65.7, 36.5 and 27.0 kg/m3 were used. The FEA models were built in the Abaqus commercial software in three-dimensional (3D) space, and analyses were performed using 3D elements. The crushable foam material model was selected for FEA from the Abaqus material model database to obtain the best correlation with the foam compression test results. The force–displacement results of the three-point bending FEA results excellently correlated with the experiments. In three-point bending experiments of the sandwich panels, elastic–plastic deformation of the core with indentation failure was observed. The lowest-density foam core sandwich beam showed the highest deformation and energy absorption performance. Also, deflection recovery was observed after load removal for all sandwiches.

Surrogate Model Based Analysis of Inter-Ply Shear Stress in Fiber Reinforced Thermoplastic Composite Sheet Press Forming

The anisotropic nature of fiber reinforced composite materials causes great challenges in predicting the inter-ply shear stress during forming. The complexity of understanding the functional dependency of inter-ply shear stress on multiple forming parameters such as blank temperature, pressure load, inter-ply slippage, and the relative fiber orientation angle of adjacent plies further limits the effort to produce a defect-free composite structure. Performing real experiments for various combinations of the mentioned parameters is both time consuming and economically costly. To overcome these difficulties, a surrogate-based analysis of inter-ply shear stress is proposed in this study. Based on the ranges of the forming parameters, computer experiments were performed. Using these experimental data, a radial basis function (RBF) based surrogate model that mimics inter-ply shear stress during composite press forming was developed. The fidelity of this model was checked with test data and found to be over 98% efficient.

Feasibility of foam forming technology for producing wood plastic composites

AbstractCellulose fiber‐containing thermoplastic composite materials are being used in an increasing number of applications produced typically by injection molding and extrusion processing methods. One potential way to manufacture thermoplastic cellulosic fiber composites is foam forming technology developed originally for paper manufacturing. This article compares the low‐density polyethylene (LDPE) and unrefined northern bleached softwood kraft pulp (NBSKP) composite materials prepared with foam forming, extrusion, and injection molding. The results show that the foam forming enabled three times higher Charpy impact strength properties and 68% higher tensile modulus compared to injection molded 30% NBSKP fiber‐containing LDPE composites without changes in composite color. Foam forming is a potential large‐scale manufacturing method for thermoplastic composite sheets used, for example, in compression molding or thermoforming.

Compositional and structural design of thermoplastic polyurethane/carbon based single and multi-layer composite sheets for high-performance X-band microwave absorbing applications

In this study, morphological features, dielectric properties, and microwave absorbing performances of thermoplastic polyurethane composite sheets prepared with solution mixing method by using different amounts and types of carbon fillers, carbon black (CB), graphite (G), carbon nanofiber (CNF), and multiwalled carbon nanotube (MWCNT) were investigated, in detail. Microstructural properties and microwave absorbing characteristics of composites were analyzed with scanning electron microscope and vector network analyzer by transmission line method, respectively. Reflection loss (RL) analyses of composites showed that CNF and CNT were more efficient than CB and G for improving the electromagnetic wave absorbing performances of sheets at low filler contents. It was found that the broadest effective absorption area (EAA) (10.03–12.96 GHz) was obtained with the sample having 3 phr of CNF. However, single layer TPU/carbon composite sheets were not effective “RADAR stealth” materials because their RL values were higher than −10 dB at X-band. Thus, multilayer (two, three, and four-layer) composite structures were designed to obtain higher microwave absorption performance within this frequency range via genetic algorithm approach. Multilayer design and modeling works showed that a four-layer composite with a total thickness of 4.8 mm yielded excellent microwave absorbing performance and broad EAA, 6.98–13.415 GHz, at X-band.

Non-destructive inspection of initial defects of PA6.6-GF50/aluminum self-piercing riveted joints and damage monitoring under mechanical static loading

A self-piercing riveting process is used to join a thermoplastic composite sheet of PA6.6-GF50 with an aluminum alloy sheet 5182 O. Two shapes of self-piercing rivet are tested: the countersunk rivet and the button head rivet. Non-destructive inspections by pulse thermography and post-mortem cross-section observations are made to assess the damage that might have occurred during the rivet piercing process. The manufacturing defects are characterized and the possible causes for their emergence are explained. Then, single-lap joint tests were carried out to determine the best joint in terms of its mechanical strength. These tests were also instrumented by various monitoring techniques such as passive thermography, digital image correlation, and acoustic emission to clarify the joint damaging behavior. Non-destructive inspections by pulse thermography are finally correlated with the thermal fields acquired by passive thermography during the mechanical test to improve the understanding of the damage mechanisms and their criticality.

Effect of Press Slide Speed and Stroke on Cup Forming Using a Plain-Woven Carbon Fiber Thermoplastic Composite Sheet

Carbon-fiber-reinforced thermoplastic (CFRTP) is viewed as a prospective material for high-cycle production of CFRP parts. This paper deals with a process whereby a preheated thermoplastic plain-woven carbon fiber fabric sheet is formed into a circular cup by a mechanical servo-press. The effects of press parameters, specifically the bottom dead center and slide speed in the forming of CFRTP cup, on the press load, pressure, internal temperature, shape accuracy, and internal structure have been investigated. A plain-woven carbon-fiber-reinforced PA6 thermoplastic sheet was used. The sheet consisted of four layers of woven 3K carbon and had a thickness of 1 mm. The sheet was heated to 320°C under a halogen heater so that it would be around the recommended temperature for forming 260°C after transfer to the mold. The sheet was pressed into a circular cup shape by a cold mold while the periphery was cramped by a heated holder so as not to cool the sheet before it was pulled into the mold cave. Die clearance was designed considering the thickness increase due to the fiber concentration during the forming. By increasing the slide stroke to the bottom dead center, the applied press load was increased and the internal structure was improved, showing no voids. By increasing the slide speed, the final press load was reduced and shape accuracy was improved through a good pressure distribution on the mold. Measurement of the surface temperature of the sheet during the forming revealed that it remained in the melting region of the resin in the case of fast slide speed, but dropped below the melting temperature in the case of low slide speed. This difference apparently led to spring-in or spring-back after the forming. The experimental results indicate that appropriate balance among press speed, bottom dead center, and sheet temperature is important in the high-cycle forming of CFRTP.

Study on resistance welding of glass fiber reinforced thermoplastic composites

Thermoplastic polymer industry has expanded a new impact with the introduction of Eco-friendly thermoplastic matrix composites (TPCs), which finds applications in medical, aerospace, electronic and automotive areas. Joints of non-conductive thermoplastic composite materials are processed by Resistance Welding (RW) by incorporating a conductive corrosion resistive conductive material, as an interlayer. Glass fiber reinforced polypropylene thermoplastic composite sheets were used for this study. The experimental set-up for resistance welding was fabricated. Welding current, clamping pressure and welding duration (Time) are the control parameters. The joining trials on composites were carried out using Taguchi method to reduce time and cost effective experimental studies. The effect of parameters which govern the quality of resistance welding of thermoplastic composites is also emphasized in this work. The purpose of this study is to determine the optimum process parameters for RW. The joints obtained were analyzed microscopically; it revealed the good integration of thermoplastic composite with the interlayer material. The mechanical strength of the joints is tested through lap shear strength testing.

An Overview of Recent Research Works on the Forming of Thermoplastic Composite Sheets

Recently, the forming of thermoplastic composite (TPC) sheets has been receiving the attention of researchers. Woven fabric TPCs have been successfully utilized in automotive, aerospace and defense industries, due to their high formability and strength. Hence, to optimize the forming process, it is essential to understand the mechanical behavior of the woven fabric and accordingly, various appropriate numerical methods are developed. A reliable simulation tool for forming is needed to obtain the optimum processing parameters, in which parts can be formed without defects, such as wrinkles. This paper explores the experimental, numerical and theoretical works conducted by many researchers to investigate the formability of TPC sheets.

Processing and Nonisothermal Crystallization Kinetics of Carbon/PPS in Single Diaphragm Forming

Single diaphragm forming (SDF) has been used in manufacturing high-quality thermoplastic composite sheet parts with complex geometries. However, temperature gradients through the thickness may exist in the composites, especially for thick, high temperature, semicrystalline composites. The thermal gradient may introduce residual stresses, which may degrade the mechanical properties or warp the part. Therefore, investigating temperature profile through the thickness during processing can improve the quality of SDF composite parts. A laboratory scale SDF with a cooling system was built for the temperature study through the thickness. Carbon fiber reinforced polyphenylene sulphide (carbon/PPS) was used for the temperature study, and the effect of cooling rate on the nonisothermal crystallization of the carbon/PPS was also investigated using differential scanning calorimeter. The start crystallization temperature and the peak crystallization temperature decrease with increasing cooling rates. A combination of Avrami and Ozawa theory was successfully used in the work for describing the crystallization kinetics, and the crystallization activation energy was determined for the carbon fiber reinforced PPS.

Mechanical properties of wetlaid lyocell and hybrid fiber-reinforced composites with polypropylene

The random wetlay process was used to fabricate thermoplastic composite sheets reinforced with chopped lyocell (regenerated cellulose from the N-methylmorpholine-N-oxide process) fibers, and with blends of lyocell and steam-exploded hardwood (SEW) fibers. Polypropylene (PP) served as matrix material in compression-molded composites reinforced with 25–65 wt.% fiber. Tensile and flexural properties of the resulting composites were compared with those reported for melt-processed (injection-molded) rayon fiber-reinforced PP composites. Association between fiber and matrix was also observed using scanning electron microscopy (SEM). Mechanical properties of wetlaid composites were found to be generally comparable with those of melt-processed composites over similar ranges of fiber loading. The fiber length-preserving advantage of the wetlay process was found to produce superior composite flexural properties. Tensile properties on the other hand, were found to require the presence of an interfacial binding agent. Results of hybrid composite studies revealed surprisingly high strength and modulus retention when as much as 60% of lyocell fibers were replaced with SEW fibers. The addition of wood fibers may potentially result in substantial savings in fiber cost.