Glass Mat Reinforced Thermoplastic Research Articles

Reinforcement of thin hot-stamped components by fiber reinforced plastic structures with optimized fatigue strength properties

Multi-material structures in the automotive industry hold great potential for lightweight design, body construction, and functionalization due to their favorable mechanical properties and reduced structural weight. The combination of metal and plastic, in particular, is commonly used to enhance the overall properties of the end product when compared to single-material structures.This paper describes a process development with a hot-stamping and an extrusion tool. By means of this tool, a thermally assisted extrusion process can be used to join GMT (Glass Mat reinforced Thermoplastics) and 22MnB5 steel in a single process step. Through adhesion, the GMT adheres to the rough surface of the AlSi(aluminum-silicon)-coated 22MnB5. Test components were manufactured and through static tests the influence of process parameters was evaluated. Assuming that the parameters determined for the reference component are already sufficient for a design in the vehicle, the reduction of the steel thickness of the structure from 1.5 mm to 1.2 mm can be recommended on the basis of the results obtained. This is accompanied by a reduction in the mass of the test structure used while maintaining or improving its dynamic and static properties. Further weight savings appear possible through further component and process optimization.

Computed tomography investigations of 3D aluminum-GMT hybrid profiles manufactured by compression molding

The main work issue is to optimize the manufacturing of hybrid profiles bearing loads defined by the automotive application, based on the monitoring of the production quality using computed tomography (CT). This offers an efficient, accurate and non-destructive inspection of the products in terms of time and costs in order to prove the production quality. The investigated parts consisted of glass mat reinforced thermoplastic (GMT) 3D structures covered by aluminum straps (AA5754) with different thicknesses. They were manufactured at varied process temperatures by compression molding. The profiles quality was evaluated by CT, where the designed and actual dimensions were compared and the porosity and the fiber distribution inside the profiles were examined. In a next step, quasi-static three point bending tests were carried out on the produced profiles in order to evaluate the impact of the production effects on the mechanical behavior. First CT results showed an inhomogeneous distribution of the fibers in the matrix especially for the profiles fabricated at lower tool temperature. Pores were also found in the areas with low concentration of fibers. After bending, the cracks tended to propagate along the fiber orientation. Consequently, the main failure mechanisms consisted in inter fiber fracture and delamination of the aluminum strap.

Analysis of GMT Composite Material-based Building Formwork

GMT (Glass Mat Reinforced Thermoplastics) is a new type of composite material made of mica and glass fiber blended into a polypropylene resin substrate, and it is durable, lightweight, high-strength, translucent and easy to install, what’s more, it can be recycled and reused to meet the needs of energy conservation and environmental protection. It is one of the mainstream building formwork materials at present. This paper analyzes and summarizes the performance of the new formwork of GMT, compares it with the traditional mainstream template, studies the problems existing in the development of GMT formwork and conducts corresponding analysis. It is pointed out that through continuous improvement of GMT formwork construction technology and the entire formwork system, its technical advantages can be fully utilized and maintained, in order to provide reference for the further development of GMT new building formwork.

In-Mold-Assembly of Hybrid Bending Structures by Compression Molding

The further development of in-mold-assembly (IMA) technologies for structural hybrid components is of great importance for increasing the economic efficiency and thus the application potential. This paper presents an innovative IMA process concept for the manufacturing of bending loaded hybrid components consisting of two outer metal belts and an inner core structure made of glass mat reinforced thermoplastic (GMT). In this process, the core structure, which is provided with stiffening ribs and functional elements, is formed and joined to two metal belts in one single step. For experimental validation of the concept, the development of a prototypic molding tool and the manufacturing of hybrid beams including process parameters are described. Three-point bending tests and optical measurement technologies are used to characterize the failure behavior and mechanical properties of the produced hybrid beams. It was found that the innovative IMA process enables the manufacturing of hybrid components with high energy absorption and low weight in one step. The mass-specific energy absorption is increased by 693 % compared to pure GMT beams.

FE Crash Modeling of Aluminum-FRP Hybrid Components Manufactured by a Hybrid Forming Process

Through the patented process of hybrid forming [1], it is possible to produce a bonded metal-plastic-hybrid component in one process step with the help of an edge-sealed pressing tool. Such a component exhibits an enormous energy absorption potential. To use this complete potential, a reliable FE-Modelling is necessary, that can exactly replicate the complex material layup consisting of an isotropic metal, a very thin bonding layer, and an anisotropic glass mat reinforced thermoplastic (GMT) for crash load case. A methodology is proposed to numerically predict the behavior of the metal GMT aluminum components. And finally, the experimental results of Hybrid components are validated for three-point bending and axial crash load cases.

Deflection Sheaves for Elevator Application in Lightweight Design

Current elevators are mostly designed as rope-dependent elevators. Main components in the roping system are the deflection sheaves which are conventional manufactured of grey cast iron. Due to the high weight of cast iron sheaves there is a high potential for reducing mass, especially when regarding aspects of effort, safety and ergonomics while assembly and maintenance in the elevator shaft. Within the framework of a R&D co-operation the Chemnitz University of Technology and the AMB Oberlungwitz GmbH developed a fibre-reinforced plastic sheave that comply with the requirements of lightweight design. The technological basic approach to realize that development is compression molding of glass-mat-reinforced thermoplastics (GMT). The project includes the whole development-chain, consisting of part design, tool design, process chain arrangement, parameter studies as well as validation of specimen. In the course of the project appeared a high potential for improvement of the part properties by alternative design solutions. In this context current activities are focused on multi material design methods such as combining GMT with other thermoplastic prepregs. In this manner it is possible to equip every local area with the specific properties that are required. For example the ribs of the sheave, that receive highest values of stress, can be made of materials with continuous-fibre-reinforcement while the basic part body consists of GMT, which is long-fibre-reinforced. This method also enables to avoid process influenced effects like the segregation of the fibre-matrix distribution in GMT. Additionally the input of different materials offers chances to inlay non-preheated prepreg blanks into the compression mould, so that the amount of the preheated material volume can be reduced. In this way cycle times and also lost of temperature due to transfer times of the heated blanks to the mould can be reduced.

Effect of temperature on formability of glass mat reinforced thermoplastic sheets with ductile dummy sheets

Given the increasing use of glass mat-reinforced thermoplastic (GMT) composites, the formability of GMT sheets is currently a topic of research. A new sheet forming process for solidified GMT was developed. In this process, a GMT sheet was sandwiched by dummy metallic sheets during deep drawing. The dummy metallic sheets acted as protective materials and media for heating the GMT sheet. In this study, tensile tests of GMT specimens were carried out under different temperature conditions. The effect of temperature on the tensile deformation was analyzed. The effect of temperature on the deep drawing process of GMT sheets with dummy sheets was further investigated. Finite element method (FEM) was conducted to simulate the deep drawing process. In the drawing force rising stage, the law of drawing force with the depth of the drawing was analyzed using FEM and experiments.

Material characteristics of random glass-mat-reinforced thermoplastic under cryogenic thermal cycles

Abstract In this study, cryogenic (77 K) to ambient (293 K) thermal shocks are induced to investigate the material behavior and failure characteristic of a random glass-mat-reinforced thermoplastic (GMT). The GMT has numerous advantages such as robust thermal conductivity, good mechanical strength, and good impact resistance. Hence, the GMT serves as an insulation material in liquefied natural gas (LNG) carrier-cargo containment systems (CCSs). In this study, 50, 100, 200, 400, and 800 cryogenic thermal cyclic shocks (77 K to 293 K) were applied to the fabricated GMT samples. The time for each cycle was 40 min, and it took up to approximately four months to completely apply the thermal cyclic shock to the specimens. The elongation, tensile strength, and elastic modulus of the testing samples obtained from the stress–strain relationship and morphologies were investigated in terms of the number of thermal cyclic shocks and strain rate. Finally, explicit formulae were proposed considering the parameters such as material properties and number of cryogenic thermal cycles to predict the material capabilities under arbitrary loading rates and cryogenic thermal cycles. It was confirmed that the degradation and defects increased with an increase in the number of cryogenic thermal cycles.

Effect of the initial fiber alignment on the mechanical properties for GMT composite materials

A glass-mat-reinforced thermoplastic (GMT) material is widely used in the automotive industry for components such as underbody shields, seat structures, front/rear bumper, and front-end modulus. Due to the higher residual length of the glass strands, GMT usually offers better mechanical properties than injection-molded fiber-reinforced thermoplastics. The GMT material is typically manufactured by compression molding (CM) of preimpregnated fibers–reinforced resin sheets called mat. Two types of mats, one with discontinuous random (RD) fibers and other with aligned continuous fibers, are considered in this study. A stack of such mats with different combinations is used to tailor the mechanical properties of the final part. During the CM, the fibers in the mat flow with the resin and change the alignment. In this study, we are presenting an approach to account for the initial condition, such as fiber length, orientation and concentration of the fibers in the mat, and process conditions used, to develop a material model for the finished part. First, a stack of mat with known fiber orientation, length, and concentration as initial conditions is simulated for CM to predict the fiber orientation in the finished part. Next, the material model for the finished parts is developed using a Mori–Tanaka homogenization approach. The fiber orientation in the finished part is mapped from the CM simulation. For the fiber concentration and fiber length distribution, we used an empirical approach. The cross section of the finished part is investigated under optical microscope, and the fiber length and concentration are estimated based on the microstructure and initial stacking of mats. The predicted fiber orientation tensor is verified with orientations measured using computerized tomography (CT) scan on actual parts. The material model is verified by comparing the predicted performance with the actual tensile and bending test results.

A Novel Method for Producing Light GMT Sheets by a Pneumatic Technique

A novel method for producing a kind of light glass-mat- reinforced thermoplastic (GMT) sheets by using a pneumatic technique is presented. The tensile and flexural properties of produced light GMT sheets, with various lengths of glass fibers and PP content, were determined experimentally. Results of the experimental investigation show that the light GMT sheets are fully suitable for engineering applications.

Gas-assisted compression moulding of recycled GMT: Effect of gas injection parameters

Gas assisted compression moulding (or GasComp) is a novel process based on the injection of nitrogen gas during a conventional compression moulding cycle, a technique originally introduced in the injection moulding industry.The gas is injected into the molten material at a preset gas inlet point, hollowing out the part and thus assisting the compressive force of the press in generating material flow. This paper presents gas injection parameter studies on polypropylene based recycled glass mat-reinforced thermoplastic (GMT). The parameters investigated are gas ramp rate, gas injection delay time, and peak pressure. The size of cavity was found to be inversely proportional to gas injection delay time. Rheological instabilities at the polymer–gas interface were observed; a phenomenon previously noted during the development of gas assisted injection moulding.

Effect of Fiber Content and Fiber Orientation on the Tensile Strength in Glass Mat Reinforced Thermoplastic Sheet

The study for strength calculation of one way fiber-reinforced composites and the study measuring precisely fiber orientation distribution were presented. Need the systematic study for the DB that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed. Therefore, this study investigated what affect the fiber content ratio and fiber orientation distribution have on the strength of composite sheet after making Glass Mat Reinforced Thermoplastic Sheet by changing fiber orientation distribution with the fiber content ratio. The result of this study will become a guide to design data of the most suitable parts design or fiber reinforced polymeric composite sheet that uses the Glass Mat Reinforced Thermoplastic Sheet in industry part, because it was conducted in terms of developing products. It studied the effect the fiber orientation distribution has on tensile strength of Glass Mat Reinforced Thermoplastic Sheet and achieved this result below. The increasing range of the value of Glass Mat Reinforced Thermoplastic Sheet’s tensile strength in the fiber orientation direction is getting wider as the fiber content increases.

Deconsolidation in glass mat thermoplastics: Influence of the initial fibre/matrix configuration

The influence of the initial configuration of glass mat and polypropylene on the deconsolidation during post-processing of the resulting composite is investigated. Deconsolidation experiments of a classic type of glass mat reinforced thermoplastic (GMT) produced by infiltration and a new type of commingled mat produced by consolidation are carried out, followed by void content measurements. A model predicting the kinetics of deconsolidation and final void content after reheating is applied to the two different systems. The numerical results completed by compressive tests carried out on both initial dry glass preforms show that the difference in fibre bundle arrangements leads to different deconsolidation kinetics and final state.

Graded glass mat-reinforced polypropylene

In the impregnation process, when pressure is applied, the dry fiber preform is first compressed and then unloads as the matrix flows within the pores. It has been shown earlier that for glass mat-reinforced thermoplastic (GMT) materials, the time to provide complete infiltration of the matrix is significantly shorter than the unloading time of the reinforcement. This effect is exploited here to control the processing time in order to provide full infiltration but limited relaxation of the fiber bed, thereby producing a graded fiber content structure. Symmetric glass fiber/polypropylene (PP) composites were impregnated for different processing times to produce parts with a higher fiber content on the surface, decreasing towards the center. The elastic modulus in bending of the GMT parts was measured by a three-point flexure test while the distribution of fibers in the matrix was quantified using optical microscopy combined with image analysis. The flexural modulus of GMT was found to decrease with the impregnation time, in good agreement with the prediction from infiltration and mechanics theory. Controlled processing could therefore be used to maximize the bending stiffness of GMT.

Impregnation of Compressible Fiber Mats with a Thermoplastic Resin. Part II: Experiments

The impregnation of compressible glass fiber mats by a thermoplastic resin in the transverse direction is investigated with application to the Glass Mat reinforced Thermoplastics (GMT) lamination process in a double belt press. Amodel proposed in Part I to simulate the kinetics of impregnation and the evolution of the fiber volume fraction profile as the resin front progresses across the fiber mat, as well as after macro-impregnation is complete, is further developed to include micro-impregnation effects. The predictions are compared with experimental results obtained using model systems such as polyethylene glycol and glass fiber mats, as well as an industrially relevant system consisting of polypropylene and glass fiber mats used in the production of GMT blanks. It is shown that significant compression of the fiber mat may occur during impregnation, with subsequent relaxation on a much longer time-scale. Also, fiber bundle impregnation generally occurs after macro-impregnation is complete, the driving force being the local pressure in the resin around the bundles, dictated by the local state of compression of the mat. The model is then used to provide guidelines for optimization of the preform impregnation conditions for a given material configuration.

Processing of long-fibre reinforced thermoplastics using the direct strand-deposition process

The use of compression moulding compounds with a thermoplastic matrix, such as glass-mat reinforced thermoplastics (GMT) and more recently long-fibre r

Micromechanical Modeling of Viscoelastic Response of GMT Composite

Experimental studies have been performed to obtain creep compliance functions of polypropylene (PP) and Glass Mat reinforced Thermoplastics (GMT) with PP matrix. It was found that both GMT and PP in the considered loading region may be considered as linear viscoelastic materials. The obtained viscoelastic compliance functions were successfully used to describe material behavior in the stress relaxation test. A micromechanical model based on the correspondence principle in the Laplace domain was developed to describe the viscoelastic behavior of GMT. This model considers the GMT composite with a given fiber orientation distribution function as consisting of an infinite number of unidirectional layers with orientations corresponding to this distribution function. The viscoelastic properties of the unidirectional layer are calculated using Hashin's concentric cylinder model that uses the experimentally determined viscoelastic properties of PP matrix. The predictions for GMT have been compared with experimental data. The model predicts rather good initial properties of GMT but it gives slightly less time dependence than compared to experimental data for both relaxation functions and compliance. The cause of the difference (debonding) between matrix and fiber, nonuniform fiber spatial distribution, stress concentrations etc.) is discussed.

Micromechanical Modeling of Viscoelastic Response of GMT Composite

Experimental studies have been performed to obtain creep compliance functions of polypropylene (PP) and Glass Mat reinforced Thermoplastics (GMT) with PP matrix. It was found that both GMT and PP in the considered loading region may be considered as linear viscoelastic materials. The obtained viscoelastic compliance functions were successfully used to describe material behavior in the stress relaxation test. A micromechanical model based on the correspondence principle in the Laplace domain was developed to describe the viscoelastic behavior of GMT. This model considers the GMT composite with a given fiber orientation distribution function as consisting of an infinite number of unidirectional layers with orientations corresponding to this distribution function. The viscoelastic properties of the unidirectional layer are calculated using Hashin's concentric cylinder model that uses the experimentally determined viscoelastic properties of PP matrix. The predictions for GMT have been compared with experimental data. The model predicts rather good initial properties of GMT but it gives slightly less time dependence than compared to experimental data for both relaxation functions and compliance. The cause of the difference (debonding) between matrix and fiber, nonuniform fiber spatial distribution, stress concentrations etc.) is discussed.

Modeling the viscoelastic response of GMT structural components

A glass-mat-reinforced thermoplastic (GMT) composite material has been fabricated from randomly oriented continuous glass fibers embedded in a polypropylene matrix. The mechanical constitution of this composite has been characterized by using a linear viscoelastic micromechanically based material model. This material model has subsequently been implemented to several finite-element computer codes for analysis of structural components fabricated from polypropylene GMT. In this paper several example problems have been studied in order to determine the applicability of this modeling approach to predicting time-dependent deformations due to creep in GMT components. These example problems have been solved by utilizing two commercially available codes: ABAQUS, and ANSYS. Furthermore, results obtained with the codes have been compared to both analytic and experimental results, with varying degrees of success. The paper details these results for each of the example problems considered herein.

Impregnation of Compressible Fiber Mats with a Thermoplastic Resin. Part II: Experiments

The impregnation of compressible glass fiber mats by a thermoplastic resin in the transverse direction is investigated with application to the Glass Mat reinforced Thermoplastics (GMT) lamination process in a double belt press. Amodel proposed in Part I to simulate the kinetics of impregnation and the evolution of the fiber volume fraction profile as the resin front progresses across the fiber mat, as well as after macro-impregnation is complete, is further developed to include micro-impregnation effects. The predictions are compared with experimental results obtained using model systems such as polyethylene glycol and glass fiber mats, as well as an industrially relevant system consisting of polypropylene and glass fiber mats used in the production of GMT blanks. It is shown that significant compression of the fiber mat may occur during impregnation, with subsequent relaxation on a much longer time-scale. Also, fiber bundle impregnation generally occurs after macro-impregnation is complete, the driving force being the local pressure in the resin around the bundles, dictated by the local state of compression of the mat. The model is then used to provide guidelines for optimization of the preform impregnation conditions for a given material configuration.