Properties Of Short Fiber-reinforced Composites Research Articles

Theory-inspired machine learning for stress–strain curve prediction of short fiber-reinforced composites with unseen design space

Computational analysis of composites is well established; however, the process is time-consuming, owing to the disparate length scales and nonlinearities involved. Therefore, the use of machine learning models to predict the mechanical properties of short fiber-reinforced composites (SFRCs) is promising when large amounts of data are lacking. However, predicting data for an unseen design space remains challenging. The use of existing theoretical models for training is a viable solution to address this issue. This paper proposes a theory-guided machine learning (TGML) framework through training deep neural networks, based on the finite element analysis dataset that considers the cohesive effect of the interface, to predict the nonlinear mechanical responses of SFRCs. Our results demonstrate that incorporating the Halpin-Tsai theory with machine learning improves the predictive performance of the model in an unseen design space. Moreover, inspired by this theory, we propose a theory-inspired two-phase machine learning (TPML) approach to further improve predictive performance. Our results indicate that TGML and TPML capture more information from the data and thus enhance predictive performance. The proposed method can be adapted to the analyses of other composites with nonlinear mechanical behaviors.

Modeling the effective elastic and viscoelastic properties of randomly distributed short fiber reinforced composites

In this work, the effective elastic and viscoelastic properties of short fiber reinforced composites (SFRCs) were investigated based on micromechanical modeling and homogenization methods. Theoretical models were proposed for revealing the mechanisms of constituents and microstructures on the elastic and viscoelastic properties of SFRCs, which were numerically validated by finite element simulations based on representative volume element models. Multiple influencing factors were comprehensively considered during the process of numerical validation. The theoretical models were then experimentally validated using experimental data of glass fiber reinforced polymer composites in the literature. The numerical and experimental results illustrate that the theoretical models can provide accurate predictions for the elastic and viscoelastic properties of randomly distributed SFRCs under various conditions in both time and frequency domains.

Closed-form analytical solutions for predicting stress transfers and thermo-elastic properties of short fiber composites

Novel analytical solutions with closed-form expressions for the stress and displacement fields of short fiber reinforced composites (SFRCs) and analytical prediction of their effective thermo-elastic properties are presented. The cylindrical SFRC unit-cells with periodic boundary conditions are subjected to axial and transverse stresses as well as thermally induced residual stresses. By comparison with available numerical and analytical solutions, it is revealed that the present closed-form solutions provide accurate stress field variations as well as accurate predictions for the effective thermo-elastic properties of SFRCs in a split second, and thus, the developed model is much more computationally efficient than numerical methods.

Modeling of geometric configuration and fiber interactions in short fiber reinforced composites via new modified Eshelby tensors and enhanced mean-field homogenization

Determination of the effective elastic properties of unidirectional short fiber reinforced composites (SFRCs) is a key fundamental requirement which is usually estimated by mean-field homogenization (MFH) methods. Available classical MFH methods only account for volume fraction and aspect ratio of the fibers and do not consider the physical cylindrical geometry of the fibers. Moreover, classical MFHs are not designed for predicting the effective properties of SFRCs with distinct packing configurations and order of fibers. In this work, new modified Eshelby tensors associated with an enhanced MFH are developed which resolve the mentioned limitations of the available MFH methods and preserve their computational efficiency. While classical Eshelby tensors used in MFHs depend only on the aspect ratio of the fictitious ellipsoidal inclusion and material properties of the matrix, the introduced modified Eshelby tensors additionally account for physical cylindrical geometry as well as interactions of the short fibers with different packing configurations. Moreover, non-uniform homogenizing eigenstrains required for accurate homogenization of the short fibers are also incorporated by the proposed analytical treatment. Predictions of the developed enhanced MFH for various packing configurations are compared with those obtained from Finite Element Method implementing periodic boundary conditions and very good agreements are observed. It is shown that packing configuration and geometrical specifications of short fibers can significantly affect the effective properties of the SFRC.

Experimental Characterization of Short Fiber-Reinforced Composites on the Mesoscale by Indentation Tests

Indentation tests are widely used to characterize the material properties of heterogeneous materials. So far there is no explicit analysis of the spatially distributed material properties for short fiber-reinforced composites on the mesoscale as well as a determination of the effective cross-section that is characterized by the obtained measurement results. Hence, the primary objective of this study is the characterization of short fiber-reinforced composites on the mesoscale. Furthermore, it is of interest to determine the corresponding area for which the obtained material parameters are valid. For the experimental investigation of local material properties of short fiber-reinforced composites, the Young’s modulus is obtained by indentation tests. The measured values of the Young’s modulus are compared to results gained by numerical simulation. The numerical model represents an actual microstructure derived from a micrograph of the used material. The analysis of the short fiber-reinforced material by indentation tests reveals the layered structure of the specimen induced by the injection molding process and the oriented material properties of the reinforced material are observed. In addition, the experimentally obtained values for Young’s modulus meet the results of a corresponding numerical analysis. Finally, it is shown, that the area characterized by the indentation test is 25 times larger than the actual projected area of the indentation tip. This leads to the conclusion that indentation tests are an appropriate tool to characterize short fiber-reinforced material on the mesoscale.

Three-scale asymptotic homogenization of short fiber reinforced additively manufactured polymer composites

In this research, prediction of mechanical properties of short fiber-reinforced composites manufactured with the help of fused filament fabrication (FFF) process is investigated. Three-scale formulation of asymptotic homogenization is employed to upscale the properties from microscale to mesoscale and from mesoscale to macroscale. Since generating microscale representative volume element (RVE) infused with short fibers requires sophisticated modeling tools, the algorithm for the microscale RVE generation is presented and discussed. Homogenization was performed for microscale RVEs with random and aligned (fibers aligned with the beads on mesoscale) fiber orientations, and for mesoscale RVEs with unidirectional and 0/90 layup formation. Tensile tests were performed for different short carbon fiber concentrations 5, 7.5 and 10% (by volume) to validate predicted homogenized properties. Moreover, to analyze the morphology of 3D printed specimens, microstructural analysis using SEM was performed on all the printed specimens. Surface morphology helped to gain more insight into the bead structure and fiber distribution. It was concluded that Young's modulus prediction using random fiber orientation has low relative errors tested in bead direction. Overall, this study has unique contribution to mechanical property prediction for FFF-made short fiber-reinforced composite parts.

Micromechanics-based analyses of short fiber-reinforced composites with functionally graded interphases

A micromechanical model for short fiber-reinforced composites (SFRCs) with functionally graded interphases and a systematic prediction scheme to determine the effective properties are presented. The matrix and the fibers are regarded to be linear elastic, isotropic, and homogeneous. Fibers are assumed to be ellipsoids coated perfectly by functionally graded interphases, which is supposed to be formed chemically or physically by the constituents near the interface. First, to analyze the grading interphase effect, layer-wise concept is followed to divide the functionally graded interphases into multi-homogeneous sub-layers. Next, to take the effect of functionally graded interphases into account, a combination of multi-inclusion method and Mori–Tanaka method is applied to predict effective elastic properties of this unidirectional SFRCs with respect to the content and aspect ratio of the inclusions. By employing coordinate transformation, spatially elastic moduli are obtained. Finally, Voigt homogenization scheme is used to obtain the overall, averaged, symmetrical elastic properties of the SFRCs. Numerical examples and analyses demonstrate the applicability of the proposed method and indicate the influences of graded interphase, orientation, and aspect ratio of inclusions as well as properties and contents of the constituents on the overall properties of SFRCs.

Experimental investigation of pull-through force of wing-type fastening inserts co-cured in long fiber prepreg sheet (LFPS)

Abstract In order to overcome the shortcomings of conventional fibrous composites, such as the limitations in the mass production of continuous fiber-reinforced composites and the inferior mechanical properties of short fiber-reinforced composites, long fiber prepreg sheets (LFPSs) are introduced in this paper. The LFPS is designed to form complex structures by thermoforming; however, highly complex shapes require mechanical fastening, after the composite parts are thermoformed. For this purpose, wing-type metal inserts embedded in the LFPS during thermoforming are investigated, and the most appropriate insert configuration is suggested. The specimens are subjected to a pull-through test, in accordance with insert parameters, such as the width and length of the insert wings, and the condition that ensures the highest pull-through force is determined. To check for wing deformation after thermoforming, the projected area and bending angle are measured through X-ray observation, and correlated with the pull-through force.

Mechanical and structural characterization of discontinuous fiber-reinforced dental resin composite

ObjectivesThis study evaluated several fiber- and matrix related factors and investigated different mechanical properties of discontinuous i.e. short fiber-reinforced composite (SFRC) (everX Posterior, eXP). These were compared with three conventional composites, microfilled G-ænial Anterior (GA), nanofilled Supreme XTE (SXTE) and bulk-fill Filtek Bulk-Fill (FBF). MethodsFracture toughness (KIC), flexural strength (FS), flexural modulus (FM), compressive strength (CS), diametral tensile strength (DTS), apparent horizontal shear strength (AHSS) and fracture work (Wf) were determined for each composite (n=8) stored dry or in water. SEM analysis of the fiber diameter (df) (n=6) and orientation (n=6) were performed. The theoretical critical fiber length (lfc) and the aspect ratio (l/d) of SFRC were calculated and the volume fraction of discontinuous fibers (Vf%) and the fiber length (lf) of SFRC were evaluated. The results were statistically analyzed with two-way ANOVA (α=0.05). ResultsThe mechanical properties of SFRC (eXP) were generally superior (p<0.05) compared with conventional composites. GA had the highest FM (p>0.05), whereas FBF had the highest AHSS (p<0.05). The fiber related properties Vf%, l/d, lf, lfc and df of eXP were 7.2%, 18–112, 0.3–1.9mm, 0.85–1.09mm and 17μm respectively. SEM results suggested an explanation to several toughening mechanisms provided by the discontinuous fibers, which were shown to arrest crack propagation and enable a ductile fracture. Water exposure weakened the mechanical properties regardless of material type. Wf was unaffected by the water storage. ConclusionThe properties of this high aspect ratio SFRC were dependent on the fiber geometry (length and orientation) and matrix ductility. Clinical significanceThe simultaneous actions of the toughening mechanisms provided by the short fibers accounted for the enhanced toughness of this SFRC, which toughness value matched the toughness of dentin. Hence, it could yield an inherently uniform distribution of stresses to the hard biological tissues.

A feasibility study of the Master SN curve approach for short fiber reinforced composites

Short fiber reinforced composite (SFRC) materials have a different fiber orientation distribution (FOD) at every point. The fatigue properties of SFRC are known to depend on the FOD. The Master SN curve (MSNC) method for predicting an SN curve for a given FOD based on the known SN curve for the reference FOD is used to predict the local SN curve of a SFRC component by relating the damage at the microscopic level to the macroscopic fatigue properties. A simplified version of MSNC method, which needs even less experimental input, uses an assumption of constant SN curve slope is also presented in this paper. The paper validates both variants of the MSNC method on three sets of experimental data on fatigue of short fiber composites and analyses their accuracy. It is demonstrated that the MSNC approach needs only one SN curve as input with no specific requirements to the fiber orientation of the test coupon. Test coupons could have either uniform fiber orientation in the thickness or a “skin core” orientation variation.

繊維の形態が短繊維‐粉体複合材料の機械的特性へ与える影響

The effect of morphology of fiber on mechanical properties of short fiber-reinforced composite was investigated. Test piece of the composite was prepared by hot pressing the mixture of powdery materials (calcium carbonate and thermosetting resin) containing the short fiber (aramid fiber). Aramid fibers were fibrillated by milling treatment and were used for reinforcement. The mechanical properties of the composites were evaluated by the fracture energy calculated by the load-displacement curves of 3-point bending test and the wear rate of abrasion test. To estimate the fiber-reinforced region in the composite, the occupied volume of the fiber was calculated by the morphology parameter of the fiber based on image analysis. The effective fiber morphology for the fracture and the wear resistance of composite was discussed on the basis of the occupied volume of the fiber.

Micromechanical Modeling of Tensile Behavior of Short Fiber Composites

A simple micromechanical constitutive model is developed for short fiber reinforced composites (SFRC) undergoing damage. The model is based on the Carman and Reifsnider approach for the prediction of mechanical properties of discontinuous fiber reinforced composites. The composite is modeled by a distributed representative element composed of concentric circular cylinders using a general 3D configuration. The micromechanical model is used to evaluate the elastic properties of SFRC, by varying the orientation distribution of the fiber, the length distribution of the fiber and the fiber–fiber interaction phenomena. The composite is assumed to behave as linearly elastic in absence of any debonding of fiber from the matrix and in the fully debonded stage. The stress–strain behavior of molded composite materials and the debonding are modeled using the Hsueh model to estimate the debonding stress for misaligned fibers. A good agreement between calculated and experimental data was achieved.