Glass Fiber-reinforced Thermoplastics Research Articles

Biaxial fatigue failure of short glass fiber reinforced polyamide 6,6: An in-depth investigation of stiffness drop and microstructural evolution

In the automotive industry, short glass fiber-reinforced thermoplastics are widely used under the hood and subjected to dynamic vibrations of the engine in multiple directions resulting in fatigue failure. Under fatigue loading, a significant portion of the strain energy is stored within the material, while the remaining portion is lost due to internal frictions and the damage occurrence. Internal friction results in heat generation, which in turn causes an increase in external temperature. This increase in temperature leads to thermal degradation of the polymer. Investigations on the cause of the stiffness drop are not widely available in the literature. Therefore, this study explores the source of the stiffness drop under biaxial fatigue loading of a polyamide 6,6 reinforced with 30 wt. % short glass fibers (PA66GF30) and distinguishes the contributions of thermal degradation and damage accumulation. The thermal evolution of the specimens was captured by means of thermography. In addition, the digital image correlation (DIC) technique was used to measure the in situ strain field during the fatigue. Despite the temperature stabilization being observed around the 10,000th cycle, the reduction in the stiffness continued until failure which was attributed to the mechanical damage accumulation and cyclic creep during the fatigue tests. Dynamic mechanical analyses (DMA) were carried out to quantify the stiffness drop with the varying temperature. From the results, it is seen that the damage accumulation and cyclic creep during the fatigue tests were responsible for the major part of the stiffness drop. Finally, scanning electron microscopy (SEM) inspection of the fracture surface was performed to identify fatigue damage mechanisms. Four unique features associated with the fatigue damage were identified: (1) debonding of fibers from the matrix, (2) polymer matrix crazing, and (3) cavitation and porosities, (4) pull out fiber ends and break on the fiber.

Four-dimensional printing of continuous glass fiber-reinforced thermoplastics

Shape memory polymers (SMPs) are a new class of materials in which their shapes can be changed over time. Despite their lightness and ease of fabrication, SMPs have very low recovery forces and are therefore inefficient when high loads are applied. To improve the mechanical properties of polymeric materials, glass fiber (GF) is commonly used as a reinforcement. The purpose of this study was to demonstrate a four-dimensional (4D) printing process using material extrusion additive manufacturing on both polylactic acid (PLA) and thermoplastic polyurethane (TPU). The goal was to improve the recovery forces in SMPs. GF roving was fed continuously into the nozzle of a three-dimensional (3D) printer to fabricate composite specimens. Also, multi-layer PLA/TPU specimens were printed. There was a measurement of shape fixity, shape recovery, and force recovery ratios. A multi-objective function analysis was performed to determine the optimum material based on recovery force priority in this study. In terms of recovery force, GF showed a superior effect. For composite specimens, shape fixity and recovery ratios decreased and increased, respectively. According to the result of optimization, PLA with 6.62 % GF proved to be the best material. PLA's recovery force has been improved by annealing heat treatment. Furthermore, cyclic experiments up to three cycles were conducted to evaluate the performance of the optimum material.

Relationship between interfacial shear strength and impact strength of injection molded short glass fiber-reinforced thermoplastics

Short glass fiber-reinforced thermoplastics (SGFRTPs) are being used to reduce carbon dioxide emissions from transportation equipment, especially domestic vehicles, because of their properties and because they are lighter than metal or ceramic materials. Interfacial shear strength (IFSS) strongly affects mechanical properties of SGFRTPs, such as the impact strength. In recent years, investigations of IFSS and impact strength have been very active. Positive correlation between these properties is often reported, but no clearly defined quantitative relation has been found. This study used the short beam method and the notched Charpy impact test to elucidate IFSS and the impact strength of injection-molded SGFRTPs with varying fiber contents: IFSS decreases concomitantly with increasing fiber content; the notched Charpy impact strength increases concomitantly with increasing fiber content. Fiber pull-out occurred along the entire fracture surface. Findings confirmed that fiber pull-out occurred with both crack initiation and propagation, indicating that energy absorption in the impact test was entirely attributable to the frictional energy necessary for fiber extraction. Based on this conclusion, a mechanical model was developed to explain the notched Charpy impact strength of SGFRTP injection molded products in terms of their IFSS, pull-out fiber length, and fiber orientation angle. The impact strength calculated using the predicted results shows good agreement with the experimentally obtained results.

A Fatigue Damage Model for Life Prediction of Injection-Molded Short Glass Fiber-Reinforced Thermoplastic Composites.

Short glass fiber-reinforced (SGFR) thermoplastics are used in many industries manufactured by injection molding which is the most common technique for polymeric parts production. Glass fibers are commonly used as the reinforced material with thermoplastics and injection molding. In this paper, a critical plane-based fatigue damage model is proposed for tension–tension or tension–compression fatigue life prediction of SGFR thermoplastics considering fiber orientation and mean stress effects. Temperature and frequency effects were also included by applying the proposed damage model into a general fatigue model. Model predictions are presented and discussed by comparing with the experimental data from the literature.

Evaluation of Self Weight Deflection Property of GFRTP Laminate at Moulding Temperature and Formability Simulation of Diaphragm Forming

The application of Glass Fibre Reinforced Thermoplastics (GFRTP) is expected to reduce the weight of automobiles. In order to use GFRTP for automotive parts, it is essential to apply Computer Aided Engineering (CAE) technology. Until now, prepreg sheets with thermosetting resin matrix are assumed to be used for materials in simulation software. When FRTP is applied for materials in simulation software, it is required to grasp the characteristics of FRTP under moulding temperature. In our previous study, a system capable of evaluating the tensile properties of FRTP laminates at moulding temperatures had been developed and their tensile properties had been evaluated. Bending stiffness under moulding temperature is also required for simulation software. While bending stiffness can be determined using Young's modulus for isotropic materials, thermoplastic prepregs have large anisotropy, especially at moulding temperature. In this study, a system that enables self-weight deflection test of thermoplastic resin laminate under moulding temperature was developed and self-weight deflection characteristics of plain weave GFRTP were evaluated. The analysed results in which the bending stiffness under the moulding temperature of GFRTP was taken into account, gave the most suitable results to the experimental results.

Process chain based data capture for a flexible and reliable life cycle inventory of a glass fiber-reinforced thermoplastic lightweight structure

In recent years, fiber-reinforced polymers (FRP) found their way into automotive serial production. This was motivated by vehicle weight reduction resulting in decreased fuel consumption in the use phase. Due to the complexity of FRP manufacturing processes, only few data for life cycle inventory (LCI) are available in databases. Furthermore, a widespread range of LCA results can be attained in dependence of the actual process parameters and part design. In order to keep up with the composite technology development, a process chain based data capturing is required taking into account deviations from the target state. This contribution therefore suggests the combination of LCI with process chain analysis. In the FOREL project FuPro, an innovative process chain for manufacturing of functionalized hollow profiles made of glass fiber-reinforced thermoplastics was developed. It comprises several steps, which cannot be evaluated using state-of-the-art databases. Hence, technologically and ecologically relevant data were captured. For this purpose, a gate-to-gate perspective was used. The process steps of plasma treatment and IR heating are selected. The presented course of action provides a resilient and flexible basis for LCA, which prospectively allows a goal-oriented multi-criteria analysis and derivation of best practice process management.

Influence of fiber orientation and weld position in welding injection-molded fiber-reinforced thermoplastics

Several publications deal with the influence of the initial fiber orientation in joining parts on the weld strength of fiber-reinforced thermoplastics. The welding partners have been sawn before welding. Preparing the joining parts after injection molding is not suitable since it is an additional manufacturing step. Since injection molding results in a non-uniform fiber orientation, there is a possibility that the position of the weld influences weld characteristics. The influence of the initial fiber orientation was investigated by preparing parts with longitudinal or transverse initial fiber orientation. Short and long glass fiber-reinforced thermoplastics with a glass fiber content of 30% have been welded by hot-plate and vibration welding. The initial fiber orientation in non-welded parts influences the weld strength: longitudinal fibers are more advantageous for the weld strength than transverse fibers. The influence of the position of the weld in injection-molded parts was investigated by welding the plates at the end of the flow path, at the sawn gate, and at the lateral side. The weld strength is similar at the gate or at the end of the flow path. For PA-GF30, the weld strength at the gate is even higher. Positioning the weld at the lateral side in injection-molded parts results in significantly lower weld strengths for short and long glass fiber-reinforced thermoplastics in hot-plate and vibration welding.

Effects of polishing on surface roughness and hardness of glass-fiber-reinforced polypropylene.

Removable partial dentures (RPDs) with resin-clasp retentive parts, which are known as non-metal-clasp dentures (NMCDs), have been used as alternatives for conventional RPDs with metal clasp, in case of aesthetic prosthodontic treatments. In this study, a profilometer and dynamic micro-indentation tests were used to investigate the effects of polishing on the surface properties such as surface roughness (Ra), dynamic hardness, and elastic modulus of high-rigidity glass-fiber-reinforced thermoplastics (GFRTPs) composed of E-glass fibers and polypropylene for NMCDs. The Ra values of the GFRTPs after polishing were significantly lower than those before polishing. The values were close to the Ra threshold level of 0.2, which corresponds to an acceptable surface smoothness for denture base materials. Polishing did not significantly change the dynamic hardnesses and elastic moduli of the GFRTPs. The fiber loading did not greatly affect the micromechanical properties of the GFRTPs because the glass-fiber reinforcement is embedded in the polypropylene matrix.

Glass fiber-reinforced thermoplastics for use in metal-free removable partial dentures: combined effects of fiber loading and pigmentation on color differences and flexural properties

PurposeThe purpose of this study was to investigate the combined effects of fiber loading and pigmentation on the color differences and flexural properties of glass fiber-reinforced thermoplastics (GFRTPs), for use in non-metal clasp dentures (NMCDs). MethodsThe GFRTPs consisted mainly of E-glass fibers, a polypropylene matrix, and a coloring pigment: the GFRTPs with various fiber loadings (0, 10, and 20mass%) and pigmentations (0, 1, 2, and 4mass%) were fabricated by using an injection molding. The color differences of GFRTPs were measured based on the Commission Internationale de l’Eclairage (CIE) Lab color system, by comparing with a commercially available NMCD. The flexural properties of GFRTPs were evaluated by using a three-point bending test, according to International Standards Organization (ISO) specification number 20795-1. ResultsThe visible colors of GFRTPs with pigment contents of 2mass% were acceptable for gingival color, and the glass fibers harmonized well with the resins. The ΔE* values of the GFRTPs with pigment contents of 2mass% obtained by using the CIE Lab system were lowest at all fiber loadings. For GFRTPs with fiber contents of 10 and 20mass% at 2mass% pigment content, these GFRTPs surpassed the ISO 20795-1 specification regarding flexural strength (> 60MPa) and modulus (> 1.5GPa). ConclusionsA combination of the results of color difference evaluation and mechanical examination indicates that the GFRTPs with fiber contents of 10 or 20mass%, and with pigment contents of 2mass% have acceptable esthetic appearance and sufficient rigidity for NMCDs.

Complex fibers orientation distribution evaluation in short glass fiber-reinforced thermoplastic (PA66 GF50)

The use of composites made of polyamide 6.6 matrix and short-glass-fibers in automobile industry is progressive due to its low density and cost. The injection molded short glass fiber-reinforced (SGFR) thermoplastics structural parts such as intake, manifold and engine mount housing, induce complex fiber orientation distributions (FOD). This microstructure governs the macroscopic properties such as the mechanical stiffness and fatigue resistance. To estimate the FOD on such industrial parts at complex angles and ribs, we rely on simulation results and micro tomography analysis. The interest of this paper is to develop a semi-automated, quick and efficient orientation tensor identification approach from 2D microscopic images, which is capable of observing relatively larger surface compared to micro tomography. We finally conclude by comparing it with micro tomography and simulation results. Furthermore, we investigate its relevance with fatigue service ability.

Characterization of mechanical properties and fracture mode of additively manufactured carbon fiber and glass fiber reinforced thermoplastics

Continuous fiber-reinforced polymer (FRP) composites have been used for many applications to create strong yet lightweight products due to their high strength-to-weight and stiffness-to-weight ratios. Aerospace [1], automotive [2], and sport [3]industries are three of the few industries that have been using FRP composites. The increasing need for prototyping and customization of fiber reinforced polymer composite parts is prompting innovations in new manufacturing processes to realize short manufacturing cycle time and low production cost, which is challenging to accomplish using conventional molding process. Fused filament fabrication (FFF) - a material extrusion additive manufacturing (AM) technique trademarked as fused deposition modelling (FDM) by Stratasys- holds promise to achieve low-cost production on continuous fiber-reinforced thermoplastic (FRTP) composites. In this paper, the FFF technique is employed to fabricate continuous carbon and glass FRTP composites and its microstructural characteristics and the resulting tensile, flexural, and quasi-static indentation characteristics of the printed composites are examined. Additionally, the fracture behavior of each test sample is evaluated and discussed in detail.

Prediction of Static and Dynamic Mechanical Properties of GFRTP Product through Injection Molding

This paper aims at evaluating the prediction accuracy of macroscopic static and dynamic mechanical properties, including damping properties, of glass fiber reinforced thermo plastics (GFRTP) obtained via computer simulations. The prediction procedure is based on the Eshelby-Mori-Tanaka approach using fiber orientation tensor. The prediction accuracy of mechanical properties depends on the fiber orientation tensor. In this paper, we compare that prediction accuracies obtained using measured fiber orientation tensor and using simulated fiber orientation tensor by resin flow analysis. Additionally, we propose a linearized damping model based on the Eshelby-Mori-Tanaka approach and modal strain energy method to predict damping property, as well as a method for evaluating the contribution of the elastic modulus in order to quantitatively comprehend the anisotropic characteristics of GFRTP.

Measuring fibre orientation in sisal fibre-reinforced, injection moulded polypropylene – Pros and cons of the experimental methods to validate injection moulding simulation

In commercial injection moulding simulation software only tools for glass fibre-reinforced thermoplastics exist, but not for natural fibres. In our research, we adapted a simulation software for sisal fibre-reinforced polypropylene. To evaluate our simulation results, three experimental methods, to measure fibre orientation are compared to each other using injection moulded sisal fibre-reinforced polymer parts: terahertz spectroscopy, μ-CT and light microscopy measurements (LMM) of microtome sections. Terahertz spectroscopy determines the main orientation over the plate thickness, but it neglects variances of fibre orientation across the plate thickness. Using μ-CT and LMM allows measuring fibre orientation at different layers across the plate thickness and to detect a shell-core effect. Care has to be taken comparing results from μ-CT and LMM, due to their differences in the slice thicknesses. The orientation found with the μ-CT correlates well with the injection moulding simulation developed for sisal fibre-reinforced polypropylene.

Inductive heating of glass fibre-reinforced thermoplastics using fibre- and wire-shaped stainless steel susceptors

This article deals with an experimental and numerical study of the inductive heating of glass fibre (GF)-reinforced thermoplastics with susceptors made of stainless steel that are embedded in them. The objective of this article is to examine the links between individual process and system parameters and the heating behaviour of fibre-reinforced plastics. Two different susceptor designs were tested in relation to their heating capability. Furthermore, it was possible to experimentally study the dependency of the space between the specimens and inductors and therefore the impact of the generator output of the induction system and inductor attachments differing in their geometric shapes in terms of heating. Moreover, it was possible to use numerical simulation to examine the heating behaviour at different frequencies. These findings indicate that it is possible to heat GF-reinforced semi-finished products by fibre-shaped susceptors. Finally, it was possible to demonstrate that the heating process can be designed by means of the frequency of the induction system and directly controlled using the generator output.

Fabrication and physical properties of glass-fiber-reinforced thermoplastics for non-metal-clasp dentures.

Recently, non-metal-clasp dentures (NMCDs) made from thermoplastic resins such as polyamide, polyester, polycarbonate, and polypropylene have been used as removable partial dentures (RPDs). However, the use of such RPDs can seriously affect various tissues because of their low rigidity. In this study, we fabricated high-rigidity glass-fiber-reinforced thermoplastics (GFRTPs) for use in RPDs, and examined their physical properties such as apparent density, dynamic hardness, and flexural properties. GFRTPs made from E-glass fibers and polypropylene were fabricated using an injection-molding. The effects of the fiber content on the GFRTP properties were examined using glass-fiber contents of 0, 5, 10, 20, 30, 40, and 50 mass%. Commercially available denture base materials and NMCD materials were used as controls. The experimental densities of GFRTPs with various fiber contents agreed with the theoretical densities. Dynamic micro-indentation tests confirmed that the fiber content does not affect the GFRTP surface properties such as dynamic hardness and elastic modulus, because most of the reinforcing glass fibers are embedded in the polypropylene. The flexural strength increased from 55.8 to 217.6 MPa with increasing glass-fiber content from 0 to 50 mass%. The flexural modulus increased from 1.75 to 7.42 GPa with increasing glass-fiber content from 0 to 50 mass%, that is, the flexural strength and modulus of GFRTP with a fiber content of 50 mass% were 3.9 and 4.2 times, respectively, those of unreinforced polypropylene. These results suggest that fiber reinforcement has beneficial effects, and GFRTPs can be used in NMCDs because their physical properties are better than those of controls. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2254-2260, 2017.

New Sandwich Structures Consisting of Aluminium Foam and Thermoplastic Hybrid Laminate Top Layers

Sandwich structures consist of one light core layer and two top layers, which form the load-bearing structure. These layers have to be stiff and strong and have to protect the structure against indentations. The main task of the core layer is to keep the top layers in place and to generate a high shear stiffness. In order to obtain the required space between the top layers, the core layer has to have a high specific volume. Different sandwich materials with aluminium or steel top layers and cores of aluminium combs, corrugated aluminium sheets or aluminium foams are already known. In order to obtain better properties in terms of strength fibre-reinforced plastics (FRP) are utilised as top layers; this is the focus of numerous of the current research studies. The sole use of these materials leads to negative effects regarding the damage and impact behaviour. New top layers with high strength and high stiffness characteristics as well as good damage tolerances are to be expected by utilising metal layers in combination with endless fibre-reinforced plastics, so called hybrid laminates. These hybrid laminates combine the positive properties of metals (e.g. ductility) and fibre-reinforced plastics (e.g. tensile strength). The focus of this investigation lies on the production and characterisation of sandwich structures with aluminium foam core layers and hybrid laminate top layers. The foam cores consist of closed pore aluminium foams produced by utilising ingot and powder metallurgical techniques. The top layers consist of glass fibre-reinforced thermoplastics and aluminium layers. The production of the sandwich materials is realised by means of thermal pressing.

첨가제 배합 및 압력에 따른 GFRTP의 기계적 특성 연구

Abstract : Glass fiber reinforced thermoplastics(GFRTP) is made by adding chemical additive to glass fabric which is strong at a high temperate, incorrodible, and good at intensity and specific gravity. Although we focused on the weight lightening, the intensity of GFRTP is also important. To remedy thermoplastic resin's inferior property of matter to thermo-hardening resin, we formed several specimen, differing the chemical additive as Homo PP, MAPP 3%, Rubber 5%, and mixed. We put pressure of 5 type on the specimens. The analyses result for the different pressure, the resin spreads evenly, then the coherence is increased. Eventually, the mechanical properties are changed. When high intensity is needed, it is good idea to use polypropylene(PP) which has good coherence with glass fabric as chemical additive. We can get better intensity when we form the resin at the optimum pressure depending on mixing of chemical additive and glass fabric than when we increase the pressure. Key words

Fiber dispersion and breakage in deep screw channel during processing of long fiber-reinforced polypropylene

Long glass fiber-reinforced thermoplastics are usually processed by pultruded granules, but glass fiber rovings were used to process long glass fiber-reinforced thermoplastics in this study. This article investigated the dispersion and breakage of fibers during extrusion processing of long glass fiber-reinforced polypropylene containing 30 wt% glass fibers at a certain processing conditions. For this study, the morphology of the surface and polished cross-section of helices was observed by digital photography, as was the morphology of the remaining fiber after burning. On this basis, the fiber/polymer system behavior in the screw channel and the dispersion mechanism of the fiber bundles were analyzed. Moreover, scanning electron microscopy (SEM) was used to observe individual fiber cross-sections to analyze the mechanism of fiber breakage. Finally, the effect of processing conditions such as temperature, screw speed and fiber content on fiber length and dispersion was studied. The results show that the fiber agglomerates composed of fiber bundles form near the barrel surface at the fiber feed point and then undergo three main stages: compression, impregnation, and dispersion. The fiber bundles separate into daughter bundles and individual fibers in different parts of the screw channel. In addition, the results indicate that the fibers can suffer tensile fracture and bending fracture during the extrusion processing. Finally, this paper includes suggestions for improving fiber bundle dispersion and reducing fiber breakage.

Laser Surface Pre-treatment of Aluminium for Hybrid Joints with Glass Fibre Reinforced Thermoplastics

Lightweight construction is a major trend in the automotive industry. Theconnection of fibre reinforced plastics with aluminium is consequently seen as promising prospect. In this regard, thermal joining can be applied for bonding of such hybrid joints. But in order to create a load bearing metal plastic joint, the surface of the metal has to be pre-treated. Recent research has shown that with laser surface pre-treatment high joint strengths are obtained. Yet there are a variety of laser sources and manufacturable surface topographies with structure sizes ranging from macroscopic to nanoscopic profiles. Within this work,macroscopic, microscopic and nanoscopic laser processed structures are created on aluminium and consequently joined to glass fibre reinforced thermoplastics of different fibre length and fibre content. High shear tensile strengths of up to 42 N/mm2 were obtained depending on the allocated material and the surface pre-treatment.

Anomalous rheological behavior of long glass fiber reinforced polypropylene

Dynamic rheological properties of PP-based long glass fiber-reinforced thermoplastics (LFT) were investigated. Weight fractions of the glass fibers investigated in the present study ranged from 0.15 to 0.5, which are higher than those of previous studies. We observed very abnormal rheological behavior. Complex viscosity (η*) of the LFT increased with the glass fiber content up to 40 wt. %. However, the η* with a weight fraction of 0.5 is observed to be lower than that of LFT with a weight fraction of 0.4 in spite of higher glass fiber content. From various experiments, we found that this abnormal behavior is analogous to the rheological behavior of a lyotropic liquid crystalline polymer solution and concluded that the abnormal rheological behavior for the LFT is attributed to the formation of a liquid crystal- like structure at high concentrations of long glass fibers.