Long-fiber Thermoplastic Composites Research Articles

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.

Long fiber thermoplastic composite for offshore drilling application - Design and prototyping

Long fiber thermoplastic composite (LFT) has been mainly used in conventional applications such as automotive because of its low cost, great specific mechanical properties, excellent impact performance, excellent corrosion resistance and ease of processibility. All of these great properties enable it a potential material candidate in unconventional applications such as offshore gas and oil drilling. This work focuses on the design optimization, prototyping, and testing of a long glass fiber reinforced polyamide 66 (glass/PA66) stop collar for stabilizing buoyancy modules on a drill pipe for offshore gas and oil drilling application. Solid model is created using CREO and structural models are constructed using ANSYS Workbench with proper boundary and loading conditions. The material properties obtained from previous material studies are used for the modeling input and geometry design is optimized to achieve the required safety factor. The glass/PA66 stop collar is then prototyped using extrusion compression molding process. The performance of the LFT stop collars is finally validated with a slip testing and a successful practical run in a drilling operation.

Tensile fatigue characterization of polyamide 66/carbon fiber direct/in-line compounded long fiber thermoplastic composites

Fiber reinforced polymer (FRP) composite materials can be advantageous alternatives to structural metals due to their high specific stiffness and strength. One potentially useful class of FRPs are Long-Fiber Thermoplastic composites (LFT) as these materials have significantly higher aspect ratios for the fibers. A possible lower cost variant of LFTs, Direct Long Fiber Thermoplastics (DLFT), where the long discontinuous fibers are created directly during the extrusion process from fiber rovings. The objective of this study was to determine the fatigue performance of DLFT composites. Therefore, tensile fatigue characterization was carried out for compression molded direct/in-line compounded (DLFT) 40% (by weight) carbon fiber/polyamide 66 composites. This characterization yielded fatigue life prediction curves (stress ratio of 0.1) for 0°, 45°, and 90° orientations with respect to flow. The evaluations showed a reasonable match to a power law approximation for the relationship of peak stress to number of cycles to failure for these materials under these test conditions (23 °C, dry as molded, R = 0.1, 3 Hz). Peak stresses at which the samples achieved 106 cycles were 105 MPa for samples oriented in the flow direction, 72 MPa for samples oriented 45° to the flow direction, and 53 MPa for samples oriented 90° to flow.

A review of Long fibre thermoplastic (LFT) composites

ABSTRACTLong fibre-reinforced thermoplastic or long fibre thermoplastic (LFT) composites possess superior specific modulus and strength, excellent impact resistance, and other advantages such as ease of processability, recyclability, and excellent corrosion resistance. These advantages make LFT composites one of the most advanced lightweight engineering materials and enable their increasing use in various applications. This review paper summarises the research and development work that has been conducted on LFT composites since their initial development. Different aspects of LFTs, such as process development, fibre orientation distribution (FOD), fibre length distribution (FLD), and their effects on the mechanical properties of LFT composites are described. The characterisation of the FOD and FLD in the LFT composites using advanced imaging technology such as high-resolution 3D micro-CT scanning technique is summarised. Research and development of LFT hybridisation and LFT additives are also discussed. Finally, conclusions are made and the future outlook of LFT composites is given.

Fabrication and Characterization of Carbon Long-Fiber Thermoplastic Composites using the LFT-D System

Fabrication and Characterization of Carbon Long-Fiber Thermoplastic Composites using the LFT-D System

Reliability in the characterization of fiber length distributions of injection molded long carbon fiber composites

The mechanical properties of a discontinuous fiber reinforced composite material are dependent on the length of the reinforcing fibers. Long‐fiber thermoplastic (LFT) composites offer a compromise between ease of manufacture and mechanical properties for structural applications and are conventionally made using fibers that are initially 10–14 mm long. However, fiber attrition during the injection molding process significantly reduces the final fiber lengths in molded composite and produces a fiber length distribution (FLD), which depends on the processing parameters. Thus, accurate FLD measurements are important for reliable predictions of the composite properties. Here, we present a detailed methodology for experimentally measuring the FLD in LFT composites based on best practices. Possible biases occurring during the measurement process are discussed and their effect on the measured FLD and averaged fiber length values are evaluated. We then employ a Mori–Tanaka implementation of the Eshelby model to predict the elastic stiffness of the LFT composite and analyze the sensitivity of the stiffness values to the biases in the FLD measurements. POLYM. COMPOS., 39:4594–4604, 2018. © 2017 Society of Plastics Engineers

Design and manufacturing of long fiber thermoplastic composite helmet insert

Long fiber thermoplastic composite (LFT) is one type of thermoplastic polymer matrix composites reinforced with discontinuous fibers above critical fiber length. It has been increasingly used in various applications due to its excellent specific strength and specific modulus in addition to its infinite shelf life, intrinsic recyclability, and high-volume processability even for complex geometries. In this work, long carbon fiber reinforced polyphenylene sulphide (LFT C/PPS) is used to prototype a helmet insert with high rigidity for stiffening a relatively soft ballistic shell. The helmet insert is designed to have a rim along its periphery in order to offer extra rigidity and facilitate a readily clip-on with the ballistic shell. Static structural analysis is carried out for evaluating the performance of the insert. Comparison was made among different patterns of the helmet insert in their rigidity. A compression molding tool is designed and machined and the helmet insert is prototyped using LFT C/PPS. A compression test is conducted for the ballistic shell integrated with the helmet insert to validate the stiffening capability of the LFT C/PPS helmet insert.

Pullout Performance of Common Construction Fasteners from Long Fiber Thermoplastic Composites

The recent increase in cyclone activity in the last 20 years has pressured the construction industry to look for alternative materials for roof construction. Although plywood is a cheap material, its mechanical properties are highly dependent on moisture content. Long fiber thermoplastics are an emerging type of plastic materials that feature enhanced mechanical properties due to high aspect ratio discontinuous fibers in a tough polymer matrix. The present study focuses on comparing the pullout strength of commonplace fasteners from plywood and long fiber thermoplastic composite panels. Specimens were tested according to ASTM standards D1761-88 and D6117-97 for mechanical fasteners in wood and long fiber thermoplastic (LFT) composites. Common construction nails like 6D, 10D and 16D and a #8 screw were used to compare the performance in terms of withdrawal. The data showed that LFT composites had withdrawal strength on average two to three times that of plywood for all tested fasteners types. Experimental data was analytically verified by APA TT-109 guidelines.

Colored inorganic-pigmented long-fiber thermoplastics

Long-fiber thermoplastic (LFT) composite materials are rapidly expanding in automotive, transportation, and recreational industry. Most of these materials are natural or black in color with a need for secondary painting of the manufactured products. Standard organic pigments and dyes are not stable above 250°C and degrade during processing. Alternatively, inorganic pigments are thermally stable to at least 800°C. High-performance inorganic pigments offer resistance to outdoor weathering, chemicals, and acids. However, in fiber-reinforced composites, the pigment causes fiber attrition and thereby shows reduction in strength. This work explores colored inorganic-pigmented LFT composites. The ability to integrate the color in the manufacturing steps eliminates the need for secondary painting. Pigment variables such as particle size, distribution, chemistry, and coatings have been investigated. The article presents the processing and performance envelopes of colored inorganic-pigmented LFTs in comparison with unpigmented standard LFTs.

Characterization of long fiber thermoplastic/metal laminates

Long fiber thermoplastic (LFT) composite/metal laminate (LML) is a hybrid composite consisting of alternate layers of metals such as aluminum and an LFT composite, which combines advantages from both the constituents. The LFT/Al laminates (LMLs) were processed by compression molding and were characterized for their Young’s modulus, mechanical strength, and low-velocity impact (LVI) properties. The average values of specific elastic modulus and specific tensile strength were approximately 20 GPa/(gcm−3) and 108.5 MPa/(gcm−3), respectively. Failure mechanisms included delamination between LFT composite and Al, fiber fracture and pullout in LFT composite, and shear fracture of aluminum and LFT composite layers. Rule-of-mixtures (ROM) predictions of laminate properties in tension compared well with the experimental values. Specific perforation energy of the laminates determined by LVI tests was 7.58 J/(kgm−2), which is significantly greater than that of the LFT composite alone, 1.72 J/(kgm−2). Overall, the LML showed significant improvement in the properties as compared to the LFT composite.

UK charity picked for energy-saving trials

Long fiber thermoplastic composite (LFT) is one type of thermoplastic polymer matrix composites reinforced with discontinuous fibers above critical fiber length. It has been increasingly used in various applications due to its excellent specific strength and specific modulus in addition to its infinite shelf life, intrinsic recyclability, and high-volume processability even for complex geometries. In this work, long carbon fiber reinforced polyphenylene sulphide (LFT C/PPS) is used to prototype a helmet insert with high rigidity for stiffening a relatively soft ballistic shell. The helmet insert is designed to have a rim along its periphery in order to offer extra rigidity and facilitate a readily clip-on with the ballistic shell. Static structural analysis is carried out for evaluating the performance of the insert. Comparison was made among different patterns of the helmet insert in their rigidity. A compression molding tool is designed and machined and the helmet insert is prototyped using LFT C/PPS. A compression test is conducted for the ballistic shell integrated with the helmet insert to validate the stiffening capability of the LFT C/PPS helmet insert.

Thermal stresses in aluminum 6061 and nylon 66 long fiber thermoplastic (LFT) composite joint in a tailcone

The present paper involves a metal/polymer joint in a tailcone in a kinetic energy penetrator (KEP), one of the ammunition types used by the military. It is currently made of aluminum 7075 alloy, which could be partly replaced by long fiber thermoplastic (LFT) composite. Two different types of aluminum insert geometries were considered, viz., beaded and threaded. Thermal stresses set in during cooling of the tailcone from the processing temperature mainly because of the difference in the values of coefficients of thermal expansion and differential cooling between the aluminum and the LFT composite. Finite element (FE) modeling was done to predict the temperature profile during the cooling of the tailcone from the processing temperature. FE results showed that the LFT composite part of the tailcone cooled faster than the aluminum insert. Experimental verification of this temperature profile was obtained by infrared (IR) thermography. Based on the temperature profile, thermal stresses at the metal/LFT composite interface were estimated using an FE model. Different magnitudes of thermal stresses were present at the aluminum/LFT composite interface owing to the nature of distribution of fibers around the insert. Magnitude of thermal stresses in the case of a beaded insert was approximately 2.5 MPa whereas in the case of a threaded insert, it was approximately 12 MPa.

Mechanical properties of long-fibre thermoplastic composites with laser drilled microperforations: 1. Effect of perforations in consolidated material

A study is presented concerning a novel technique for enhancing the formability of long-fibre thermoplastic composites. A laser beam has been used to drill arrays of holes into PEEK/AS-4 and PPS/AS-4 carbon-fibre composite pre-preg. These arrays were designed to cut all the fibres to pre-determined lengths. Holes were of the order of 150 μm in diameter, with average fibre length reduced to either 20, 50 or 100 mm. Once perforated, the pre-preg material was consolidated into laminates in an autoclave. Tensile testing has been used to evaluate the effects of the laser drilling. Experimental data show that the perforation process does not affect the stiffness, but strength is reduced somewhat. This reduction is dependent on the distribution of holes and the nature of the laminate. The strength of notched laminates was found to be unaffected by perforation. Off-axis testing has been used to evaluate the transverse and shear strength of both PEEK- and PPS-based composites, and this has been linked to observed failure mechanisms. Finite element modelling has been used to confirm that shear failure parallel to the fibres is initiated by the stress concentrating effect of the perforations.

Mechanical properties of long-fibre thermoplastic composites with laser drilled microperforations: 2. Effect of prior plastic strain

An examination is presented of how the mechanical properties of a PPS-based carbon-fibre composite, in which an array of fine holes had been generated by laser drilling, are affected by the prior imposition of large plastic strains. This was done in order to explore how a typical high temperature forming operation would be likely to change the microstructure of such microperforated material and hence to affect its mechanical properties. Tensile strains of up to 200% were imposed in a drawing operation, with imposed transverse constraint sufficient to ensure that the fibres remained within the plane of the specimen. After drawing, specimens were tested to failure in tension at room temperature. It has been found that the strength and stiffness of the material remains relatively close to the corresponding values prior to deformation for strains of up to about 50%. Above this level, both strength and stiffnesses were observed to decrease fairly rapidly. These results have been explained in terms of the microstructural changes which accompany the drawing process.