Long Fiber Reinforced Thermoplastics Research Articles

Critical length prediction for fiber breaking in injection molded of long-fiber reinforced thin-walled products

Fiber length is one of the vital factors in determining the properties of long fiber reinforced thermoplastics (LFRT). However, many factors may generate fiber breakage in the injection molding process of LFRT, such as friction, melt shear, injection rate, etc. Especially for thin-walled products, owing to the relatively narrow mold cavity and frozen layer near the mold wall, it’s usually difficult for the fibers to move freely with the melt, leading to fiber breakage under the shear stress of the flow field eventually. In such a situation, the existing buckling breakage model based on the assumption fibers immersed in the flow field being in an unconstrained state is no longer applicable. In this paper, a new model for calculating the critical length of constrained fiber in thin-walled injection molded products is developed. A typical long glass fiber reinforced polypropylene thin-walled product was employed to verify the reliability of the model. The high-precision fiber length analyzer was used to calculate the fiber length distribution at different distances from the injection port. At the same time, the length distribution at the corresponding position was predicted via the model. The average prediction accuracy in the three sampling sections is 87.8%, 91.4% and 83.6%, respectively. The results show that the proposed model can effectively predict the fiber length distribution of injection molded thin-walled products. This conclusion provides important support for further accurate calculation of the mechanical properties of products.

Experimental and homogenized orientation-dependent properties of hybrid long fiber-reinforced thermoplastics

This research presents a investigation of long fiber-reinforced thermoplastics (LFT) with mixed fiber types, combining experimental analysis with numerical modeling techniques. By accurately predicting the stiffness of mixed fiber composites, the design margin between mono fiber reinforced materials can be effectively exploited, facilitating the use of such materials. For this purpose in particular, a novel application of the Mori–Tanaka approach with two different inclusions guaranteeing symmetric stiffnesses is presented. This is a method that has never been used before in field studies. In addition, the study integrates fourth-order plate-averaged orientation tensors measured and subsequently interpolated to improve the accuracy of the modeling. Consistency with the established shear-lag modified Halpin–Tsai method is demonstrated, confirming the suitability of both approaches for predicting the tensile modulus of GFLFT and CF+GFLFT. However, discrepancies between predictions and experiments for CFLFT are attributed to the complex microstructure of the material caused by bundling and poor dispersion of the CF. Furthermore, the study reveals remarkable hybridization effects within the mixed fiber LFT, particularly evident in the 22% increase in elongation at break observed in CF+GFLFT compared to CFLFT. Overall, this research significantly advances the understanding and predictive capabilities regarding mixed fiber LFTs, which opens up a new design space of specific properties. This provides valuable insight for future research and industrial applications.

Fibre and failure characterization in long glass fibre reinforced polypropylene by X-ray computed tomography

Long fibre reinforced thermoplastics (LFTs) have become important in recent years, due to outstanding mechanical properties (such as high strength, high stiffness, and excellent impact behaviour). Nevertheless, there is still a lack of knowledge regarding the failure micromechanics of LFTs. This publication focuses on the qualitative and quantitative analysis of influencing factors for failure initiation in long fibre reinforced thermoplastics. Existing and new methodologies are combined for detailed analysis of the local microstructure and micromechanical behaviour. In situ investigations of the LFT via X-ray computed tomography (CT) and subsequent fibre and mechanical characterization based on the volume data were performed. A measurement workflow for the decision on the scanning area before starting a scan series is suggested. The difficulties in fibre orientation analysis of long, curved fibres are revealed by a comparison of different evaluation approaches. Fibre straightness, fibre volume fraction, fibre orientation and fibre end accumulations are investigated in detail. Local strains are determined with digital volume correlation (DVC) and related to the true stress along the measured specimen length. The investigations showed that the test specimens do not necessarily break at the position of the smallest cross-section under uniaxial loading conditions. The failure behaviour of LFTs is strongly influenced by the local microstructure and thus the combination of various microstructural factors such as fibre bundles, fibre ends, local fibre volume fraction and orientation.

An assessment of new materials that are light weight for use in automobiles to improve fuel efficiency

Global energy demand is currently contributing to a severe problem of rising fuel prices for automobile users. One solution is to reduce the weight of the car body to improve fuel efficiency and reduce fuel costs. The choice of car body material can achieve this purpose. This paper will present the criteria such as stiffness, strength, and density to determine the suitability of substituting traditional materials, such as mild steel and carbon steel, with new materials High Strength Steel (HSS), aluminum alloys, and Long Fiber Thermoplastic (LFT). A literature review of the research is done to showcase the challenges traditional materials experience and how the development of these three new materials can overcome these challenges. Results from the case study show the feasibility of implementing these new materials in an automobile. More future research should be conducted to overcome the challenges and limitations posed by using these new materials, focusing on the low-cost replacement, manufacturing, and co-joining techniques of car body parts.

Approaching Polycarbonate as an LFT-D Material: Processing and Mechanical Properties.

Long-fiber thermoplastic (LFT) materials compounded via the direct LFT (LFT-D) process are very versatile composites in which polymers and continuous reinforcement fiber can be combined in almost any way. Polycarbonate (PC) as an amorphous thermoplastic matrix system reinforced with glass fibers (GFs) is a promising addition regarding the current development needs, for example battery enclosures for electromobility. Two approaches to the processing and compression molding of PC GF LFT-D materials with various parameter combinations of screw speed and fiber rovings are presented. The resulting fiber lengths averaged around 0.5 mm for all settings. The tensile, bending, Charpy, and impact properties were characterized and discussed in detail. Special attention to the characteristic charge and flow area formed by compression molding of LFT-D materials, as well as sample orientation was given. The tensile modulus was 10 GPa, while the strength surpassed 125 MPa. The flexural modulus can reach up to 11 GPa, and the flexural strength reached up to 216 MPa. PC GF LFT-D is a viable addition to the LFT-D process, exhibiting good mechanical properties and stable processability.

Thermoplastic composite connecting rods

Engineering carbon fiber thermoplastics have been used in the development and optimization of composite connecting rod(s) with design requirement of bearing 14,000 N and 1 mm maximum deflection. The studies featured engineering thermoplastics- 30 wt percent carbon fiber poly ether ether ketone (C-PEEK) long fiber thermoplastics (LFT) injection over molded in conjunction with 70 wt percent carbon/polyphenylene sulfide (C-PPS) and carbon/poly ether imide (C-PEI) tapes. Over molding of thermoplastic tapes has been investigated in terms of number of tape winding around the small and big end, and different winding patterns within the connecting rod geometry. The design was progressively optimized for the geometry of the connecting rod, i.e., increasing the wall thickness of the small end and width of the center section. The effect of over molded metal bushing with C/PEEK LFT at the bearing surfaces was also investigated. The material and geometry optimization successfully met 14,000 N while several design iterations were necessary to meet the 1 mm deflection limit constraint. Finite element analysis (FEA) was adopted to optimize the increase of the width of the center section width and wall thickness of the small end. The optimized composite connecting rod was estimated to be 78% lighter than the steel incumbent.

Influence of Polymer Matrices on the Tensile and Impact Properties of Long Fiber-Reinforced Thermoplastic Composites

To investigate the influence of polymer matrices on the tensile and impact properties of long fiber-reinforced thermoplastic (LFT) composites, composites of long basalt fiber-reinforced thermoplastic were developed in this work. Two types of polyethylene, namely 8008 and 100S, and two types of polyethylene, namely C4220 and K8303, were chosen as the matrices. The fiber volume fractions were set as 2.8%, 5.9%, 8.1%, and 10.6%. The melt flow index (MFI), crystallinity, tensile properties, impact strength, and fracture morphology of the neat polymers and the corresponding composites were tested. The composites of 8008 showed the highest tensile strength since neat 8008 showed a much higher MFI value and crystallinity. The composites of 8008 and K8303 showed a much higher tensile modulus since the neat thermoplastic showed a higher tensile modulus than the other two composites. The polymer toughness was the factor that determined whether the polymer could be toughened by fibers. Moreover, the interfacial shear strength was calculated and compared with the matrix shear strength, based on which fracture modes of the LFT were predicted. Effective methods were proposed for further improvement of the mechanical properties. The results of this paper were essential for attaining the anticipated properties when designing LFT composites.

Relation between injection molding conditions, fiber length and mechanical properties for highly reinforced long fiber polypropylene

AbstractA complete study on the relation between the injection molding parameters and the resulting fiber length, orientation and mechanical properties is presented for highly reinforced long fiber thermoplastic (LFT) polypropylene (PP). It has been found that the longest fibers obtained are the ones processed with the lowest backpressure and the highest screw speed. The backpressure gains importance over screw speed when the amount of glass fiber reinforcement increases, contrary to what was found for less reinforced thermoplastics. The injection speed does not influence the fiber breakage phenomena, while it has great importance in fiber orientation and thus on the tensile strength, especially when the weight fiber average length is below 1000 μm. When this average is over 1000 μm, fibers begin to weave a mesh that thickens the core region and hinds its orientation, reducing the tensile strength but improving impact resistance.

Lightweight design approach of an LFT-metal multi-material vehicle door concept

This work presents a new approach to design and validate an economical lightweight multi-material roof-integrated vehicle door concept made of long-fiber thermoplastics (LFT) and metals with the consideration of package constrain, critical static and crash loading cases. A novel “two-ring” door structure is introduced, which consists of a major load-bearing region and a minor load-bearing but highly function-integrated region. This concept design concentrates on using cost-efficient lightweight materials, such as aluminum, LFTs and uni-directional tapes (UD-Tapes), as well as corresponding mass-production methods. Using the topology and parameter optimization along with the load anisotropy analysis, the rib structure on the door concept is optimized and the effective usage of UD-Tapes is guaranteed. In comparison to the steel reference, the final LFT-metal multi-material door concept achieves 20% weight reduction with a comparable or improved mechanical performance.

Using long fiber thermoplastic composites as substitutes for metal: design considerations

Long fiber thermoplastic (LFT) composite design studies often emphasize fiber content but are sketchy on fiberorientation, fibermatrix interface, and mold design. At PlastiComp we use an all-inclusive approach to successfully deploy LFT materials in metal replacement applications. Examples show how long carbonfiber compounds were successfully substituted for die-cast magnesium by redesigning the application for injection molding production, achieving tailored fiber architectures at key stress locations through strategic gate locations, as advised through finite element analysis (FEA) and mold flow analysis (MFA), and maximizing mechanical properties through optimized molding processes.

Development of PA6/GF Long-Fiber-Reinforced Thermoplastic Composites Using Pultrusion and Direct Extrusion Manufacturing Processes

The mechanical properties of polyamide 6 glass fiber (PA6/GF) long-fiber-reinforced thermoplastic (LFT) composites were characterized by studying the process conditions in terms of manufacturing methods (direct extrusion and pultrusion) and material characteristics (void content and fiber volume fraction). The LFT composites prepared through the pultrusion process have higher mechanical properties than those prepared via the direct extrusion process. The PA6/GF composite prepared via pultrusion had the tensile and flexural strengths of 233 MPa and 338 MPa, respectively. The impact strength measured using the Izod method was 296 J/m, which is 64% higher than that of the composite fabricated via the direct process. The optical microscope images showed that the glass fiber length of the pultruded composites is longer than the fiber length of the direct composites, leading to higher mechanical properties of the LFT composites prepared through the pultrusion process. Moreover, the interfacial shear strength between the resin and the fiber, measured via single fiber pullout tests, can account for the higher fiber reinforcing efficiency. If the void content of a composite is sufficiently small to not be detrimental to the composites, the mechanical properties are observed to be proportional to the fiber volume fraction of the composites.

Mechanical Property of Long Glass Fiber Reinforced Polypropylene Composite: From Material to Car Seat Frame and Bumper Beam.

Long Fiber Reinforced Thermoplastic (LFT) is a lightweight, high-strength, and easy-to-recycle new vehicle composite material, and has good mechanical properties, heat resistance, and weather resistance, which has found increasing application in automobile industry. It is of importance to understand the relationship between micro phase, macro-mechanical properties and the structural performance of automobile components. This article evaluates the performance of LFT from the level of material to automobile components. The mechanical properties of LFT were numerically and theoretically predicted to provide instruction for the next material choice. Two typical structural components, namely, car seat frame and bumper beam, were selected to evaluate the performance of LGF/PP compared with other competing materials in terms of mechanical properties and cost. In the case of the same volume, the seat frame of 40% LECT/PP composite material is lighter and cheaper, which is conducive to energy saving and emission reduction. It was shown that the 40% LECT/PA66 car bumper beam had a higher energy absorption ratio, lighter weight, higher specific energy absorption, and advantageous material cost. LFT is a promising candidate for existing automobile components with its performance fulfilling the requirements.

Combination and development of carbon filament tows: Application of coextrusion with long fiber‐reinforced thermoplastics

AbstractIn this study, long fiber‐reinforced thermoplastics (LFT) and coextrusion are applied to wrap carbon fiber tows in a thermoplastic polyurethane (TPU) outer layer. In this way, the proposed wrapped yarns have a sheath–core structure. Scanning electron microscopy observation reveals that TPU and carbon fiber tows form a physical combination that allows TPU to further enhance the tensile strength of carbon fiber tows by 35.87%, which is 19.62 ± 1.88 MPa. The tensile strain of carbon fiber tows also improves. LFT and coextrusion are performed to produce successive carbon fiber tows that can be successfully fabricated into textiles, possessing good fabric flexibility. The technique of carbon fiber tows can be applied to mass production feasibility for the field of carbon fiber composites.

Novel modeling approach for fiber breakage during molding of long fiber-reinforced thermoplastics

Long fiber-reinforced thermoplastics (LFTs) are an attractive design option for many engineering applications due to their excellent mechanical properties and processability. When processing these materials, the length of the fibers inevitably decreases, which ultimately affects the mechanical performance of the finished part. Since none of the existing modeling techniques can accurately predict fiber damage of LFTs during injection molding, a new phenomenological approach for modeling fiber attrition is presented. First, multiple controlled studies employing a Couette rheometer are performed to determine correlations between processing conditions, material properties, and fiber length reduction. The results show shear stress and fiber concentration impact fiber damage. Based on these findings, a phenomenological model to predict breaking rate and unbreakable length of a fiber under giving conditions is developed. The model is based on the beam theory with distributed hydrodynamic stresses acting on a fiber. Fiber–fiber interactions are accounted for and correlated with the fiber volume fraction via a fitting parameter. The model tracks both the number-average and weight-average fiber length during processing, which can in turn be used to extract the fiber length distribution.

Effects of A, B, and S components on fiber length distribution, mechanical, and impact properties of carbon fiber/ABS composites produced by different processing methods

AbstractCarbon fiber/ABS composites with different acrylonitrile, butadiene, and styrene components were produced via extrusion/injection and long fiber thermoplastic (LFT)/injection molding processes, respectively. The effect of the components on fiber length distribution, tensile, flexural, impact, and dynamic mechanical properties of the composites was investigated. The properties of carbon fiber/ABS composites produced using 12 mm‐long LFT pellets were markedly higher than those produced using extruded pellets made with 12 mm‐long chopped carbon fibers. Uses of LFT pellets were preferable to enhancing the mechanical properties of carbon fiber/ABS composites. The tensile, flexural, and dynamic mechanical properties were increased in order of ABS750sw > ABS720 ≥ ABS780 > ABS740, whereas the impact strength was increased in order of ABS740 > ABS780 > ABS720 ≈ ABS750sw. Less carbon fiber damages and less carbon fiber length degradation upon LFT processing resulted in longer fiber length distribution and higher fiber aspect ratio in the composites with LFT pellets, indicating a beneficial reinforcing effect, which was responsible for the increased mechanical properties of ABS composites, particularly with ABS750sw. The results were agreed with each other, significantly depending on the A, B, and S components, being supported by fiber length distribution, fiber aspect ratio, and fracture surfaces.

Melt extruded versus extrusion compression molded glass-polypropylene long fiber thermoplastic composites

Long fiber thermoplastic (LFT) composites are processed either with extrusion compression or fiber injection processes. The properties of LFT materials are highly influenced by processing techniques, which lead to different porosity contents, fiber length distributions, and fiber orientation distributions. It is important to understand the various LFT processing techniques and their effects on mechanical, thermal, and microscopic properties. This work considered LFT sheets processed via extrusion, which offers highly aligned fibers (referred to as “Tecnogor composites”), and LFT composites produced via extrusion compression molding (ECM), which offers a random distribution of fibers. Tecnogor composites exhibited higher flexural strength (35–65%), flexural modulus (132–172%), tensile strength (39–52%), tensile modulus (67–75%), and Izod impact resistance (195–220%) than the random LFT composites. This response was attributed to the aligned fibers in Tecnogor composites. Mathematical models including Halpin-Tsai and Lavengood-Goettler were used to predict and compare the Young’s modulus of Tecnogor and ECM composites, respectively.

On the bead design in LFT structures: the influence of manufacturing-induced residual stresses

Abstract In the design of long fibre reinforced thermoplastic (LFT) structures, there is a direct dependency on the manufacturing. Therefore, it is indispensable to integrate the manufacturing influences into the design process. This not only offers new opportunities for material- and load-adapted designs, but also reduces cost-intensive modifications in later stages. The goal of this contribution is to make the complexity manageable by presenting a method which couples LFT manufacturing and structural simulations in an automated optimization loop. Herein, the influence of linear-elastic, local anisotropic material properties as well as residual stresses resulting from the compression molding of LFT on the stiffness-optimized design of beaded plates is investigated. Based on the simulation studies in this contribution, it can be summarized that the resulting bead height and flank angle, considering anisotropies and residual stresses, are smaller compared to isotropic modelling. As a conclusion, the strength constraint limits the maximum bead height and the flank angle needs to be additionally chosen as a consequence of the local fibre orientations and residual stresses resulting from manufacturing. Optimized bead cross sections are only valid for a specific system under investigation, as they depend on the defined boundary conditions (load case, initial charge geometry and position, fibre orientations, etc.).

Automotive hybrid design production and effective end machining by novel abrasive waterjet technique

Hybrid designs with the combination of metal and long fiber reinforced thermoplastics (LFT) offer a great opportunity to reduce component weight for automotive applications. Production costs are typically high due to complex processes and challenging end machining. A complete manufacturing process chain for simultaneous hybrid design production is presented. Hybrid forming, a manufacturing process combining metal sheet forming, LFT compression molding and bonding, was developed to manufacture an automotive lightweight component, finally end machined by innovative waterjet techniques. Besides optimizing waterjet end machining strategies, waterjet controlled-depth machining was used to remove LFT material selectively, resulting in increased hybrid production flexibility.

Manufacturing and characterization of continuous fiber-reinforced thermoplastic tape overmolded long fiber thermoplastic

Light-weight construction, design freedom, integration of functions, and compelling cost element are desired by Original Equipment Manufacturers (OEMs) and their suppliers. The emergence of overmolding of continuous-discontinuous reinforcement enables design freedom and ability to tailor stiffness, strength, and damage tolerance for structural applications. In this work, long fiber thermoplastics (LFT) are overmolded with continuous fiber-reinforced thermoplastic (CFRTP) tape are combined using extrusion compression molding process to evaluate the structural performance. The CFRTP tape overmolded LFT samples were characterized using nondestructive and destructive techniques to track fiber alignment, fiber distribution, manufacturing defects, interfacial bonding of the tape – LFT and effect of CFRTP tape on LFT. Mode 1 fracture toughness, G1c for tape overmolded LFT was higher by 25–30% compared to literature reported G1c. This response was attributed to excellent fiber distribution, good fiber wetting, and absence of voids at the interface. Three-point bend test indicated that CFRTP tape overmolded LFT composites were better able to resist damage under the bending load compared to constituent LFT composite. Flexural strength of the overmolded composite was higher by 119–142%, and modulus higher by 77–65% compared to constituent LFT composite. Simulated flexural results accurately represents the mechanical behavior of composites. The penetration energy of tape overmolded LFT composites determined by LVI test was in the range of 27.66–30.15 J, which is significantly higher than constituent LFT composite, 7.76 J. CFRTP tape overmolded LFT composite exhibits progressive fiber fracture, matrix cracking, and interfacial debonding failure, whereas, constituent LFT composite showed catastrophic fiber fracture.

Long fibre-reinforced thermoplastic theoretical model for energy absorption analysis based on impact performance

This article deals with initial material selection and design method of long fibre-reinforced thermoplastic (LFT) based on impact resistance requirements. In this study, effects of material properties and impact condition, including total fibre thickness, fibre aspect ratio and impactor diameter, on the minimum penetration energy of LFT plates are analysed based on experiments and validated numerical models. Mathematical expression is established between them. Applicability of the original model for LFT plate with different fibre aspect ratios subjected to different impactors is discussed. The minimum penetration energy is used as the bridge between energy absorption characteristics and material parameters, impact condition. Finally, an updated theoretical model for energy absorption analysis is proposed. We conclude that the updated semi-empirical model is a valuable tool for a first stage material selection and design.