Short Fiber Composite Materials Research Articles

Strain rate and temperature dependence of short/unidirectional carbon fibre PEEK hybrid composites

Short fibre and hybrid carbon fibre PEEK composite materials were tested in tension and compression under quasi-static and high strain rate conditions to observe the strain rate dependence. Multiple temperatures including room temperature, ＋85 and −50 °C were used to investigate the temperature dependence of the materials. The hybrid laminate comprised a consolidated short fibre core reinforced with outer UD plies in the 0°orientation to provide maximum reinforcement whilst minimising the quantity of expensive UD composite used. Under compression, the beneficial effect of the hybridisation strategy was observed for all high-strain rate testing conditions, where the hybrid laminate outperformed the response of the individual constituents in terms of strength and strain rate dependency. The outer unidirectional (UD) layers contributed to confining the short fibre core, providing superior structural integrity. Under tension, the response was dominated by the UD layers with a 288% increase in strength at room temperature over the short fibre material. However, in the high temperature quasi-static case, the strength was dramatically reduced, by 64%, due to the debonding of the UD reinforcement. This study shows the suitability of hybrid composites for impulsive applications and provides material parameters for the future design of composite structures subjected to impact events.

Discrete element approach to simulate debonding process in 3D short glass fibre composite materials: Application to PA6/GF30

This paper discusses the development of a numerical approach based on the Discrete Element Method (DEM) to simulate the interfacial debonding in Short Fibre Reinforced Composites (SFRC). For that purpose, we consider a hybrid lattice-particle approach based on a cohesive beam model. Already used to study composite materials, we aim to extend this concept to investigate the damage mechanism of SFRC in particular the PA6/GF30. To do so, a specific technique to estimate the Representative Elementary Volume (REV) of PA6/GF30 is proposed and discussed. The suggested discrete modelling is then validated by comparison with micromechanical approaches and experimental data for elastic behaviour predictions. At this time, the development of a DEM-based framework to model SFRC composite represents one of the novelties of this work. A mixed-mode discrete damage model based on an energetic formulation (which constitutes another originality of this paper) is subsequently discussed. To do so, the cohesive beam model is first implemented and validated through standard delamination problems. Thereafter, the case of SFRC is explored, focusing on the case of UniDirectional (UD) single fibre and aligned short-fibre composites under bending test. Simulation results in terms of onset and propagation of the debonding of fibre/matrix interface confirm the potential of the discrete modelling presented.

Processing, mechanical characterization, and micrography of 3D-printed short carbon fiber reinforced polycarbonate polymer matrix composite material

The objective of this research is to perform the processing and mechanical characterization on 3D-printed high-temperature polymer (polycarbonate) reinforced with short carbon fiber (SCF) composite material fabricated with the help of fused filament fabrication process. For this study, different SCF volume fractions (3%, 5%, 7.5%, 10%) with varying printing speed (25, 50, 75 mm/s) are taken as the input variables. It was observed that tensile, flexural, compressive properties and micro-hardness were greatly affected by varying the input processing parameters. To find the orthotropic properties of 3D-printed specimens, tensile properties are analyzed on 0° in the X-Y plane, 90° in the X-Y plane, and 90° in Z-axis. Scanning electron microscopy (SEM) is performed to study the effect of fiber breakage, fiber distribution, fiber accumulation, and fiber length on the mechanical performance of the final part. After performing mechanical testing, investigation of microstructural behavior of tensile, flexural, and compressive samples is accomplished using SEM. From the micrograph analysis and mechanical testing, it was noticed that fiber behavior inside the composite has created a great influence in deciding the mechanical performance of the final part. Micromechanics and classical lamination theory phenomena are followed to determine the effective young’s modulus of 3D-printed samples mathematically. Printing direction and reinforcement percentage are found out to be the most influential parameters in deciding the final properties of 3D-printed specimens by using the statistical tool ANOVA. Response surface methodology is used to determine the optimum parameters to get good-quality print with SCF-reinforced PC.

Study on Surface Dmage and Residual Strength of Short Fiber Composite Material due to Sphere Impact

Study on Surface Dmage and Residual Strength of Short Fiber Composite Material due to Sphere Impact

Microstructure and Mechanical Properties of a Near-α-Titanium-Alloy/TiB Composite Prepared in situ by Casting and Subjected to Deformation and Heat Treatment

This paper presents the results of our study of the microstructure and mechanical properties of a short-fiber composite material based on Ti/TiB prepared in situ by casting. We used a two-phase titanium alloy VT18U (Ti–6.8Al–4Zr–2.5Sn–1Nb–0.7Mo–0.15Si) as the matrix material for this study. The addition of boron and pure titanium into the titanium alloy led to the formation of 6.5 vol % TiB fibers. Two deformation treatments were used in this research. The first was isothermal forging in two directions (2D) at temperatures of the upper part of the α + β phase field to provide an elongation of TiB fibers along one direction; the second treatment was 3D forging at temperatures of the α + β phase field to ensure the refinement and random orientation of borides for fabricating material with isotropic properties as far as possible. The deformed semifinished samples of the composite materials and of the matrix alloy were annealed. The composite materials demonstrated noticeably higher strength and creep resistance compared to the matrix alloy and retained an acceptable plasticity. The microstructural studies of the fractured samples showed a high adhesion strength of boundaries between the matrix and the TiB fibers, which is retained even with increasing test temperature irrespective of the orientation and morphology of the borides. The failure of the composites begins with the breaking of borides and is followed by the ductile fracture of the matrix material.

Evaluating the number of fibre orientations required in homogenization schemes to predict the elastic response of long fibre sheet moulding compound composites from X-ray computed tomography measured fibre orientation distributions

For predicting the mechanical response of mis aligned short fibre composite materials a two step homogenization procedure coupled with orientation averaging of the elastic material properties is often used. Orientation averaging is not valid for long fibre composites due to non-symmetric strain localization tensors. A method to homogenize the stress for mis aligned long fibre composites using the Functionally Graded Interphase (FGI) approach is presented and the results are compared to two step Mori Tanaka homogenization. The microstructure of long fibre Sheet Moulding Compound (SMC) composite is evaluated using X-ray micro computed tomography. The measured fibre orientation distributions are used to evaluate the number of representative fibre orientations required to predict the stress state of the SMC due to applied strains. It is found that 60 orientations are required to capture the stress response of the long fibre SMC composite using the FGI model and two step Mori Tanaka model.

FEA of flow field of short fiber and rubber composite material during extrusion process

Die structure is one of the most important factors that impacts short fibers orientation during extrusion process. As a result, the effects of two kind of die structure which is dam-die and expansion-die on flow field including pressure field, velocity field and the velocity of short fiber and rubber composite material during extrusion process has been researched by Polyflow. The FEA results about the flow field of the short fiber and rubber composite material indicate that, compared with the two kind of dam-die and expansion-die, the dam die is better for short fibers get orientation in rubber matrix during extrusion process than the expansion-die.

Research on Extrusion of Rubber Composites Reinforced by Short Fibers Orientation Based on FEA

In recent years, rubber composites reinforced by short fibers has been researched deeply, because of its good performances such as higher wear resistance, higher cut resistance and so on. Some research results indicated that if short fibers get orientation in rubber composites, the performances of rubber products could be promoted greatly. But how to make short fibers get orientation in rubber matrix during extrusion is still a real problem. And there are many parameters affect the short fibers orientation. So, in this paper, the effects of die structure including expansion-die and dam-expansion-die on extrusion flow field of short fiber and rubber composite material during extrusion process has been researched by Polyflow. And the FEA results about the pressure field, velocity field and the velocity vector of the rubber composites flow field indicate that, comparing with expansion-die and the dam-expansion-die, the latter one is better for the extrusion process of rubber composites and making short fibers get radial orientation in rubber matrix.

Effect of Sphere Diameter on Residual Strength Degradation of Short Fiber Composite Material due to Sphere Impact

Effect of Sphere Diameter on Residual Strength Degradation of Short Fiber Composite Material due to Sphere Impact

Study on residual strength of short fiber composite material due to sphere impact

In this study, a small sphere impact test was carried out using a short fiber reinforced composite material to investigate damage due to impact. After the impact test, the bending test was carried out and the residual strength was investigated. As the results, when the impact speed of the sphere is low, only indentations are formed on the surface of the specimen. It was found that radial cracks occurred in addition to indentations as the impact speed of the sphere increased. As a result of the four point bending test, the residual strength tended to decrease as the impact speed increased. It was found that the fracture position can be classified into three types: (a) rupture at a position irrelevant to the indentation, (b) rupture along the edge of the indentation, (c) rupture across the indentation.

Fatigue Damage Evaluation of Short Carbon Fiber Reinforced Plastics Based on Phase Information of Thermoelastic Temperature Change.

Carbon fiber-reinforced plastic (CFRP) is widely used for structural members of transportation vehicles such as automobile, aircraft, or spacecraft, utilizing its excellent specific strength and specific rigidity in contrast with the metal. Short carbon fiber composite materials are receiving a lot of attentions because of their excellent moldability and productivity, however they show complicated behaviors in fatigue fracture due to the random fibers orientation. In this study, thermoelastic stress analysis (TSA) using an infrared thermography was applied to evaluate fatigue damage in short carbon fiber composites. The distribution of the thermoelastic temperature change was measured during the fatigue test, as well as the phase difference between the thermoelastic temperature change and applied loading signal. Evolution of fatigue damage was detected from the distribution of thermoelastic temperature change according to the thermoelastic damage analysis (TDA) procedure. It was also found that fatigue damage evolution was more clearly detected than before by the newly developed thermoelastic phase damage analysis (TPDA) in which damaged area was emphasized in the differential phase delay images utilizing the property that carbon fiber shows opposite phase thermoelastic temperature change.

Progressive damage analysis of a rate-dependent hybrid composite beam

A hybrid beam combined of a molded woven fabric beam and over injected or compressive molded short fiber composite material, are manufactured and three point bending tests with different loading rates and two different boundary conditions are performed. Since the experimental results demonstrate a rate dependent behavior of the beam, then to predict its mechanical behavior under different loading velocities two strain rate sensitive progressive damage models have been developed based on Continuum Damage Mechanics approach. For internal reinforcing constituent of the beam which dominated by matrix, the matrix failure index of Hashin-Rotem’s failure criterion was chosen and for outer part which governed by fibers the maximum stress theory is considered as damage initiation indicator. For both models Lapczyk-Hurtado’s approach is followed to capture damage propagation. To account for rate-dependent material properties, where is needed, equations derived from a logarithmic formula, are utilized. The models are applied on the commercial finite element software of ABAQUS using user-written subroutine based on explicit numerical method. The numerical results are verified by the bending tests and it is shown that the numerical results of the proposed models have shown better agreement with experimental results of compressive molding technology than back injected one.

短繊維CFRPにおける熱弾性温度変動の位相情報を用いた損傷評価

Carbon Fiber-reinforced plastic (CFRP) is widely used in such as aviation and structural material because it is an excellent material in specific strength and specific rigidity in contrast with the metal. Short fiber composite materials is receiving a lot of attention because it is excellent in moldability and productivity, but it shows complicated behavior of fatigue fracture due to the random fibers orientation. The infrared thermography is expected to be a usable non-destructive testing technique for composite materials. In this study, Thermo-elastic stress analysis was applied to the short fiber composite for evaluation of fatigue damage. The range of thermoelastic temperature change and the phase difference between the thermoelastic temperature change and load stress are calculated during the fatigue test. The range of thermoelastic temperature change corresponds to the propagation of delamination, like thermoelastic damage analysis (TDA). The phase difference shows the change distribution corresponding to the propagation of delamination. The fatigue damage evaluation technique using the phase difference, which called the thermoelastic phase damage analysys (TPDA) is suggested.

An incremental-secant mean-field homogenization method with second statistical moments for elasto-plastic composite materials

In this paper, the incremental-secant mean-field homogenization (MFH) scheme recently developed by the authors is extended to account for second statistical moments. The incremental-secant MFH method possesses several advantages compared to other MFH methods. Indeed the method can handle non-proportional and non-monotonic loadings, while the instantaneous stiffness operators used in the Eshelby tensor are naturally isotropic, avoiding the isotropization approximation required by the affine and incremental-tangent methods. Moreover, the incremental-secant MFH formalism was shown to be able to account for material softening when extended to include a non-local damage model in the matrix phase, thus enabling an accurate simulation of the onset and evolution of damage across the scales. In this work, by accounting for a second statistical moment estimation of the current yield stress in the composite phases, the plastic flow computation allows capturing with a better accuracy the plastic yield in the composite material phases, which in turn improves the accuracy of the predictions, mainly in the case of short fibre composite materials. The incremental-secant MFH can thus be used to model a wide variety of composite material systems with a good accuracy.

Microstructure and Mechanical Properties of Ti–TiB Based Short-Fiber Composite Materials Manufactured by Casting and Subjected to Deformation Processing

Microstructure and Mechanical Properties of Ti–TiB Based Short-Fiber Composite Materials Manufactured by Casting and Subjected to Deformation Processing

The effect of short fiber composite base on microleakage and load-bearing capacity of posterior restorations

Objectives: To determine the marginal microleakage of Class II restorations made with different composite base materials and the static load-bearing capacity of direct composite onlay restorations.Methods: Class II cavities were prepared in 40 extracted molars. They were divided into five groups (n = 8/group) depending on composite base material used (everX Posterior, SDR, Tetric EvoFlow). After Class II restorations were completed, specimens were sectioned mid-sagitally. For each group, sectioned restorations were immersed in dye. Specimens were viewed under a stereo-microscope and the percentage of cavity leakage was calculated. Ten groups of onlay restorations were fabricated (n = 8/group); groups were made with composite base materials (everX Posterior, SDR, Tetric EvoFlow, Gradia Direct LoFlo) and covered by 1 mm layer of conventional (Tetric N-Ceram) or bulk fill (Tetric EvoCeram Bulk Fill) composites. Groups made only from conventional, bulk fill and short fiber composites were used as control. Specimens were statically loaded until fracture. Data were analyzed using ANOVA (p = 0.05).Results: Microleakage of restorations made of plain conventional composite or short fiber composite base material showed statistically (p < 0.05) lower values compared to other groups. ANOVA revealed that onlay restorations made from short fiber-reinforced composite (FRC) as base or plain restoration had statistically significant higher load-bearing capacity (1593 N) (p < 0.05) than other restorations.Conclusion: Restorations combining base of short FRC and surface layer of conventional composite displayed promising performance related to microleakage and load-bearing capacity.

Investigation of thermal stress distribution in fiber-reinforced roller compacted concrete pavements

Roller compacted concrete (RCC) is a kind of concrete that is used in pavement construction. RCC has the strength and performance of conventional concrete with the economy and simplicity of asphalt. Unfortunately, this type of concrete is less sensitive to cracking in relation with drying shrinkage and thermal stresses. In this way, reinforcement of RCC with fibers would be a useful solution. The main aim of this study was therefore investigating into thermal stress distribution in fiber-reinforced RCC (FRRCC) pavements. Firstly, the thermal stress induced in fiber-reinforced rigid pavements was modeled by using “thermal expansion law” in short fiber composite materials and “Eshelby’s model” extended from the “theory of elasticity”. Consequently, an instrument was developed to measure the heat gradient in FRRCC samples at different origin temperatures of 40℃, 60℃, and 80℃. Steel and polypropylene fibers were used to prepare FRRCC specimens. The analytical results showed that fiber modulus, fiber volume fraction, fiber Poisson’s ratio, and fiber coefficient of thermal expansion determine the induced thermal stress in FRRCC pavements. The analytical outcomes were straightly correlated with the experimental results.

Effects of defects on the tensile strength of short-fibre composite materials

Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found. These new experimental findings highlight a problem of some existing strength criteria, which are principally based on a rule of mixture of the strengths of constituent phases, and not on the weakest link. Only a weak correlation was found between stress concentration induced by the critical agglomerate and the strength. A strong correlation was however found between the stress intensity and the strength, which underlines the importance of the size of largest defects in formulation of improved failure criteria for short-fibre composites. The increased use of three-dimensional imaging will facilitate the quantification of dimensions of the critical flaws.

A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites

An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting th ...

Effects of Short Fiber Reinforcement on the Local Damage of Concrete Plates under High Velocity Impact Loading

This study presents the effects of short fiber reinforcement on the local damage of concrete plates subjected to high velocity impact. In a series of tests, three short fiber composite materials were used. Firstly, static bending tests were conducted to reveal mechanical properties in tension of the short fiber reinforced concrete. Then, high velocity impact tests were carried out to examine the effects of short fiber reinforcement on the local damage of concrete plates. Failure mode and strain behavior on the back surface of the short fiber reinforced concrete plates demonstrated that short fiber reinforcement was very effective in reducing the local damage.