Mechanical Properties Of Thermoplastic Composites Research Articles

Micromechanical deformation modeling and failure prediction of thermoplastic composites

Based on the multi-scale progressive homogenization theory, a micromechanical model is proposed that can predict the plastic deformation of thermoplastic fiber-reinforced composites. By developing microscopic representative volume elements (RVEs) that include three materials phases: fiber, matrix and fiber–matrix interface, the effect of elastic–plastic material behaviors and interface debonding on the mechanical properties of thermoplastic composites can be considered. Employing this model, the deformation and failure process of carbon fiber reinforced PEEK composite is studied, considering the effects of random size and distribution of carbon fiber, as well as the ratio of interface debonding. It can be found that the yielding strength is most sensitive to the proportion of interface debonding compared to Young’s modulus and ultimate strength. Interface debonding has the most significant impact on the mechanical performances of thermoplastic composites by introducing a higher degree of plastic deformation into the polymer matrix and changing the evolution path of material damage.

Interfacial Engineering Methods in Thermoplastic Composites: An Overview.

The paper critically analyzed different interfacial enhancing methods used in thermoplastic composites. Although the absence of cross-linked polymer chains and chemical bonds on solidification enables the thermoplastics to be remelted, it creates weak interfacial adhesion between fibre reinforcements and the thermoplastic matrix. The weak fibre-matrix interface bonding reduces the efficiency with which the applied load can be transferred between these composite constituents, causing the composite to fail prematurely. Their need for high-temperature processing, poor compatibility with other polymer matrices, and relatively high viscosity render thermoplastics challenging when used to manufacture composite laminates. Therefore, various methods, including nanoparticles, changing the polarity of the fibre surface by plasma etching, chemical treatment with ozone, or an oxidative attack at the fibre surface, have been applied to improve the fibre/matrix bonding in thermoplastic composites. The fabrication steps followed in these techniques, their progress in research, and the associated toughening mechanisms are comprehensively discussed in this paper. The effect of different fibre-matrix interfacial enhancement methods on the mechanical properties of thermoplastic composites is also deliberated.

Effects of recycling and hygrothermal environment on mechanical properties of thermoplastic composites

Recyclability of nine types of composites including natural and mineral fillers in polypropylene and nylon matrix have been studied through injection molding and mechanical grinding. No significant degradation in mechanical properties of natural fiber composites occurred after recycling or water absorption tests. In contrast, glass fiber composites showed decrease in tensile strength and modulus by up to 45% and 40%, respectively after five rounds of recycling mainly due to severe fiber attrition. Glass bubbles breakage occurred after recycling, which diminished its ability to provide lightweighting. Only glass fiber reinforced nylon composites were affected by hygrothermal conditioning, which were characterized as a function of recycling. At saturation point, water absorption for nylon composites was 7.7% by wt. after 45 days of immersion, which significantly affected the mechanical properties. Tensile strength and modulus of glass fiber nylon composites reduced from 88.4 MPa and 5.6 GPa to 36.2 MPa and 1.8 GPa, respectively.

Physical and Mechanical Properties of Thermoplastic Composites Filled with Wood Flour of Underutilized Chaste Tree

The potential use of a lignocellulosic filler, Vitex agnus-castus plant (Chaste tree), which is a deciduous invasive shrub, in thermoplastic composites was investigated. The stems of chaste trees with a diameter of 5-10 cm from Mugla city, Western Turkey, were used for the study. The different amounts (0 to 50 wt%, by 10 % increments) of the wood flour passing through the screen openings of 0.237 mm were added to the polypropylene matrix. Premixed raw materials were put into the volumetric feeder of the twin-screw extruder. The extruder barrel temperature was gradually increased from 170 °C (feeding zone) to the die zone (190 °C) at a constant screw speed (40 rpm). Then, the dried granules were hot-pressed into the 4 mm thick WPC panels at 2 MPa and 190 °C for 5 min. 3 wt% of maleic anhydride grafted polypropylene (MAPP) was added as compatibilizer into the formulation. The WPCs showed an increase in the thickness swelling (0.58 to 5.68 %) as the amount of the filler increased from 10 to 50 wt% in the polypropylene. The bending strength of the polypropylene composites increased from 33.9 to 44.8 MPa as the amount of the chaste wood flour was increased to 30 wt%, but further increase caused the decrease in the tensile strength (25.7 MPa). As for the bending modulus, it increased from 815 to 3250 MPa when the wood content reached 50 wt%. The tensile modulus increased from 1690 to 2253 MPa when the wood content arised from 10 to 50 wt%. The tensile strength, tensile modulus, flexural strength and flexural modulus of the unfilled polypropylene were found to be 19.6 MPa, 1505 MPa, 30.2 MPa and 664 MPa, respectively. According to the test results, it was concluded that the 30-40 wt% of Vitex agnus-castus wood could be efficiently used in the polypropylene composites for the semi-building applications such as decking or siding. The evaluation of underused invasive chaste wood in the production of tWPC production may result in an effective way to utilize this resource.

Multiscale simulation on nonlinear mechanical properties of cellulose composites with different fiber morphologies

The effect of fiber morphology on mechanical properties of thermoplastic composites reinforced by cellulose microfibers was investigated by multiscale numerical analysis. The homogenization theory was employed for scale coupling, and representative volume element (RVE) models with random fiber orientation was generated based on the random sequential adsorption (RSA) algorithm. The effects of fiber aspect ratio and aggregation on nonlinear mechanical properties were investigated. The elastic properties and maximum tensile stress were found to vary by 26.8% and 39.6%, depending on the fiber aspect ratio, and by 5.95% and 4.20%, depending on fiber aggregation.

An Investigate of the Effect of Manufacturing Parameters on the Mechanical Properties of Thermoplastic Composites

An Investigate of the Effect of Manufacturing Parameters on the Mechanical Properties of Thermoplastic Composites

Quasi-static and low-velocity impact responses of polypropylene random copolymer composites with adjustable crystalline structures

Currently, the effect of cooling rates on mechanical properties of continuous glass fiber-reinforced isotactic polypropylene (CGF/iPP) composites cannot be well revealed, due to the imperfect impregnation containing voids, limited selection of crystalline structures (i.e., boundary defects and lamellae thickness) and impact energy. Moreover, compared to the polypropylene random copolymer (PPR) with toughness-rigidity balance, the brittleness of iPP and incompatibility of iPP/elastomer system also limit the further improvement of impact resistance. Furthermore, to date, the influence of cooling rates on mechanical properties of CGF/PPR composites has not been reported. Herein, we reveal the influence mechanism of multiple crystalline structures on quasi-static, and on low-velocity impact behavior of CGF/PPR composites based on perfect impregnation. Results show that the tensile strength and impact resistance under perforation threshold both increase first and then decrease with the increased cooling rate, while the impact resistance at non-perforation threshold gradually improves. Severe boundary defects mask the contribution of other crystalline structures, resulting in the lowest tensile strength. After overcoming boundary defects, the type of lamella is the most important factor for the effect of stress transfer. In the case of non-perforation damage, laminate with the smallest crystallinity and the widest size distribution only suffers from subcritical damage. The stiffness of amorphous area generated by the density of tie chains and chain entanglements becomes the decisive factor for improving impact resistance of laminate above perforation threshold. This work may pave the way for improving mechanical properties of thermoplastic composites via generating specific crystalline structures.

Thermoplastic Pultrusion: A Review.

Pultrusion is one of the most efficient methods of producing polymer composite structures with a constant cross-section. Pultruded profiles are widely used in bridge construction, transportation industry, energy sector, and civil and architectural engineering. However, in spite of the many advantages thermoplastic composites have over the thermoset ones, the thermoplastic pultrusion market demonstrates significantly lower production volumes as compared to those of the thermoset one. Examining the thermoplastic pultrusion processes, raw materials, mechanical properties of thermoplastic composites, process simulation techniques, patents, and applications of thermoplastic pultrusion, this overview aims to analyze the existing gap between thermoset and thermoplastic pultrusions in order to promote the development of the latter one. Therefore, observing thermoplastic pultrusion from a new perspective, we intend to identify current shortcomings and issues, and to propose future research and application directions.

Effect of MgOH/TiO2 on flame retardancy and mechanical behavior of composite

Flame retardancy and mechanical properties of thermoplastic composites containing magnesium hydroxide (MH) and titanium dioxide (TiO2) were investigated. Low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) blend was incorporated with flame retardants (FRs) MH and TiO2 in different wt.% ratios. Effect of flame retardants on fire resistance and mechanical properties of composites were characterized through UL94, limiting oxygen index, thermogravimetric analysis, tensile and impact tests. The flame retardancy was improved to V-0 with LOI value 24.9% due to the synergistic effect of both FRs. The thermal gravimetric analysis showed that the mass residue obtained was increased from 5 wt% to 25 wt%. Mechanical properties such as tensile strength and modulus of LDPE/EVA was improved from 6.4 MPa to 7.1 MPa and 127 MPa to 133 MPa respectively after the incorporation of both FRs. Impact energy absorbed was also improved from 27.8 KJ mm−2 to 35.2 KJ mm−2.

Surface Modification of Carbon Fibers by Grafting PEEK-NH2 for Improving Interfacial Adhesion with Polyetheretherketone.

Due to the non-polar nature and low wettability of carbon fibers (CFs), the interfacial adhesion between CFs and the polyetheretherketone (PEEK) matrix is poor, and this has negative effects on the mechanical properties of CF/PEEK composites. In this work, we established a modification method to improve the interface between CFs and PEEK based chemical grafting of aminated polyetheretherketone (PEEK-NH2) on CFs to create an interfacial layer which has competency with the PEEK matrix. The changed chemical composition, surface morphology, surface energy, and interlaminar shear strength were investigated. After grafting, the interlaminar shear strength (ILSS) was improved by 33.4% due to the covalent bonds in the interface region, as well as having good compatibility between the interface modifier and PEEK. Finally, Dynamic Mechanical Analysis (DMA) and Scanning Electron Microscopy (SEM) observation also confirmed that the properties of the modified CF/PEEK composites interface were enhanced. This work is, therefore, a beneficial approach towards enhancing the mechanical properties of thermoplastic composites by controlling the interface between CFs and the PEEK matrix.

EFFECT OF VARIOUS PULLING SPEEDS ON THE MECHANICAL PROPERTIES OF VARIOUS FIBER MIXTURE COMBINATIONS OF POLYAMIDE 6 AND 6.6 MATERIALS

Nowadays, thermoplastic composites have increasingly wide application areas due to their high stiffness and impact strength properties, superior fracture toughness, long duration of raw material shelf life and ease of production processes. Besides, they provide safer work environment. In this study, it has been examined that how the pulling speeds effects mechanical properties of thermoplastic composites. Non-reinforced, 15 percent reinforced and 30 percent reinforced polyamide 6 and polyamide 6.6 samples are produced with using plastic injection molding method and they are subjected to tensile testing at five different pulling speeds using the Tensile Testing Device. The results obtained from testing and those gathered from the plastics manufacturer company are compared with data obtained from the literature to check mechanical properties of thermoplastic composites which have been used in pulling speed test. It is observed that the experimental results were highly consistent with those in literature. According to these results, the positive effect of higher pulling speeds is observed. In this way, the different types of unreinforced and fiber glass reinforced polyamide 6 / polyamide 6.6 samples behavior under different pulling speeds have been determined. The results are in similar behavior with all types of polyamides. In order to gain an understanding of the effect of the overall testing procedure for all speeds, stress–strain graphics are constructed. Article DOI: https://dx.doi.org/10.20319/mijst.2018.41.162179 This work is licensed under the Creative Commons Attribution-Non-commercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Microstructures and mechanical properties of thermoplastic composites based on polyarylate/nylon6 islands‐in‐sea fibers

Polyarylate (PAR) fiber‐reinforced nylon6 composites are manufactured by molding uniaxially‐aligned islands‐in‐sea fibers at different temperature (190–210°C), pressure (0.69–6.89 MPa), and time (1–10 min). For the purpose, the islands‐in‐sea fibers, in which 74 PAR islands act as reinforcing microfibers and nylon6 sea part serves as a semicrystalline matrix in the thermoplastic composites, are prepared by a conjugate melt‐spinning. The tensile and dynamic mechanical properties of the thermoplastic composites are investigated by taking into account their microstructural and morphological features, which are influenced by the molding conditions, as examined by differential scanning calorimetry, 2D‐X‐ray diffraction, scanning electron microscopy, micro‐CT, and polarized optical microscopy (POM) analyses. The thermoplastic composite manufactured at 200°C and 2.07 MPa for 3 min is found to have maximum tensile strength of ∼630 MPa and initial modulus of ∼70 GPa owing to multiple synergistic effects such as high crystallinity of nylon6 matrix, good alignment of PAR microfibers, interfacial crystallization of nylon6 on the reinforcing PAR microfibers, and low porosity. The findings of this study indicate that PAR/nylon6 inland‐in‐sea fibers can be utilized effectively for manufacturing high performance thermoplastic composites for sports, automotive, and protective applications. POLYM. COMPOS., 40:E484–E492, 2019. © 2018 Society of Plastics Engineers

Studies on mechanical properties of thermoplastic composites prepared from flax-polypropylene needle punched nonwovens

Abstract Natural fiber reinforced thermoplastic composites using flax and polypropylene were prepared using compression molding process. Needle punched nonwovens were used as preforms for preparing the composites. Three variables namely fiber weight proportion, areal weight of the mat, and needling density were chosen for the study. Modified Taguchi L18 experimental design with dummy variable was chosen for the study and the effect of the above variables on tensile, flexural, and impact properties of the composites were studied. By altering the fiber weight proportion and areal weight of the mat, tensile and flexural properties improved. An increase in 34% of tensile strength and 40% of flexural strength has been observed. Impact properties of the composites were significantly altered by modifying the process variables. Increasing the needling density led to a decrease in overall mechanical properties of the composites.

Acoustical and mechanical properties of thermoplastic composites from discarded carpets

Abstract Without additional matrix or reinforcement, compression molded composites from waste polypropylene (PP) carpets/nylon (PA) carpets or PP carpets/polyester (PET) carpets have higher mechanical properties and sound absorption than traditional jute/PP composites. Large amount of carpets have been discarded every year, leading to waste of petro-based materials and serious environmental pollution. Fabrication of composites from discarded carpets via compression molding could save petroleum resources and alleviate environmental pressure. In this research, the compression molded composites from waste PP/PA carpets or PP/PET carpets showed good mechanical properties, sound absorption and water stability. Compared to the jute/PP composites, nylon 6,6 (PA66)/PP carpet composites had 37% and 9% higher flexural strength and impact resistance, as well as 45% and 10% higher sound absorption and water stability, indicating their potential for transportation and construction industries.

The Effect of the Melt Viscosity and Impregnation of a Film on the Mechanical Properties of Thermoplastic Composites.

Generally, to produce film-type thermoplastic composites with good mechanical properties, high-performance reinforcement films are used. In this case, films used as a matrix are difficult to impregnate into tow due to their high melt viscosity and high molecular weight. To solve the problem, in this paper, three polypropylene (PP) films with different melt viscosities were used separately to produce film-type thermoplastic composites. A film with a low melt viscosity was stacked so that tow was impregnated first and a film with a higher melt viscosity was then stacked to produce the composite. Four different composites were produced by regulating the pressure rising time. The thickness, density, fiber volume fraction (Vf), and void content (Vc) were analyzed to identify the physical properties and compare them in terms of film stacking types. The thermal properties were identified by using differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). The tensile property, flexural property, interlaminar shear strength (ILSS), and scanning electron microscopy (SEM) were performed to identify the mechanical properties. For the films with low molecular weight, impregnation could be completed fast but showed low strength. Additionally, the films with high molecular weight completed impregnation slowly but showed high strength. Therefore, appropriate films should be used considering the forming process time and their mechanical properties to produce film-type composites.

Investigation into the mechanical properties of thermoplastic composites containing holes machined by a thermally-assisted piercing (TAP) process

A thermally assisted piercing (TAP) process has been investigated as an alternative to current methods of machining holes in thermoplastic composites. The spike force/displacement responses during piercing were affected by both the processing temperature and the size of the heated area, as were the resultant microstructure and subsequent mechanical performance. Overall, the results suggest that for advanced manufacturing of thermoplastic composites, good tensile and compressive open-hole properties are produced in the TAP process when using small heated areas and higher temperatures.

Design of microwave plasma and enhanced mechanical properties of thermoplastic composites reinforced with microwave plasma-treated carbon fiber fabric

Microwave plasma equipment was designed and manufactured to improve the interfacial bonding and mechanical interlocking between carbon fiber fabric (CFF) and the polymer matrix. Tensile specimens for the composites reinforced with the as-received and microwave plasma-treated CFFs were prepared using high-speed fabrication with a polymerizable and low-viscosity cyclic butylene terephthalate (CBT) oligomer matrix. Compared with the polymerized CBT (pCBT) matrix, the tensile strengths of the as-received and plasma-treated CFF reinforced composites (CFFRCs) were enhanced by approximately 362.5% and 436.3%, respectively. A high carbon fiber content of 70vol.% was achieved without introducing pores and/or defects into the CFFRC due to the low viscosity and high impregnation characteristics of the CBT resin. It was confirmed that the microwave plasma can increase the surface roughness of the tested CFF without varying the chemical composition and defect level of the CFF. In addition, the interfacial bonding and mechanical interlocking between the CFF and polymer matrix were improved.

Processing and mechanical properties of thermoplastic composites based on cellulose fibers and ethylene-acrylic acid copolymer

The melt processing and the tensile mechanical properties of composites consisting of 30 wt% softwood kraft pulp cellulose fibers and ethylene-acrylic acid copolymer (EAA) with 7% acrylic acid content were studied. The compounding techniques used were extrusion mixing performed with a single screw extruder and elongation dispersive mixing performed with the injection-molding machine. All blends were injection-molded in a final step. Fiber length, fiber content, and mechanical properties were measured and the number and the size of the fiber aggregates were determined by microscopy analysis. It was concluded that two passes of elongation dispersive mixing had a beneficial effect on the mechanical properties, which could be related to the fewer and smaller amounts of aggregates. The different types of processing performed had a small or insignificant effect on the fiber length since the fiber lengths measured were within the same range as that of the starting material. POLYM. ENG. SCI., 52:1951–1957, 2012. © 2012 Society of Plastics Engineers

Preforms and composites manufactured by novel flax/polypropylene cowrap spinning method

In the past decade, natural fiber composites with thermoplastic matrices have been embraced by many composite manufactures for its properties such as lightweight and low cost. Reinforced cowrap spinning yarns and thermoplastics offer a potential for low-cost manufacturing of complex-shaped and good, drapable composite parts, due to reduced impregnation times and resin flow distance during processing. In this article, the cowrap spinning yarns were produced by cowrap spinning method with flax and polypropylene (PP) and then woven to fabric preforms. The natural flax fibers were twistless in yarns and preforms, and PP served as a carrier for flax and prevented damage to flax fibers during processing, and became the polymer matrix in the final composites. To get an even distribution of fibers and thermoplastic resins in preforms and different flax fiber content, the main spinning parameters (hollow spindle twist and hollow spindle rotational speed) were analyzed and optimized. Besides fabric structure, the parameters affecting the mechanical properties of flax/PP preforms and composites were investigated. The fabric density, fabric structure (including plain, twill, and basket weave), and yarn tensile orientation (at 0°, 90°, and 45°) had a great influence on the tensile strength and elongation of preforms. Different pretreatments on flax/PP were investigated, and the microstructure and mechanical properties of thermoplastic composites showed improved wettability of impregnation and good adhesion and bonding interface between flax fiber and PP matrix in composites.

The Influence of Interfacial Adhesion on the Predicted Young's Modulus of Mica-Reinforced Nylon-6

ABSTRACT Particle-filled polymer composites have become attractive because of their wide applications and low cost. Various factors influence the mechanical properties of thermoplastic composites. Of these, the aspect ratio of the reinforcement, interfacial adhesion, and binder content are the most important. Other than these, the particle size and particle size distribution of the reinforcement also influence the mechanical properties. In this paper, injection molded mica composites were investigated, using nylon-6 as a binder. Many models are available to predict the Young's modulus of the composites. A theoretical model for Young's modulus by Lewis and Nielsen was used to predict the Young's modulus of the composites. Tetra isopropyl titanate (TYZOR® TPT) was used to modify the adhesion between the reinforcement and the binder by mixing it with the reinforcement prior to compounding. It was found that Young's modulus was greater than the predicted values.