Longitudinal Tensile Loading Research Articles

The strength prediction model of unidirectional fiber reinforced composites based on the renormalization group method

When unidirectional fiber reinforced composites are subjected to longitudinal tensile loading and reach a critical failure state, they experience a sudden transition from local damage to catastrophic failure, commonly termed as an avalanche event. This paper integrates the self-organized criticality theory (SOC) concepts into the prediction of longitudinal tensile strength of composites and establishes a strength prediction model of composites based on the renormalization group method (RGM). The predictions of the RGM model are successfully validated against experimental results in the literatures, and it demonstrates relatively acceptable predictive accuracy compared to classical strength criteria. Compared to other state-of-the-art prediction models considering stochastic fiber strength distribution, the RGM model effectively provides strength statistics for fiber bundles of any size and describes the occurrence of composites avalanche failure induced by local stress concentration. This present model can be very conveniently implemented as a User Material Subroutine (UMAT) for finite simulations, facilitating practical prediction of the strength of composites structures.

Micromechanical modeling for longitudinal tensile property of unidirectional CFRP considering dispersion of fiber properties

Longitudinal tensile failure prediction has always been the focus of research on unidirectional (UD) Carbon Fiber Reinforced Polymer (CFRP). In this paper, the longitudinal tensile tests of unidirectional T800 grade carbon fiber reinforced epoxy resin composite were carried out first. The experimental stress–strain curves show that there are obvious progressive damages before the final failures of the specimens. However, this phenomenon is usually neglected in most of the existing investigations and tests to only obtain elastic modulus and ultimate strength. Thus, a Representative Volume Element (RVE) model based on micromechanics was established using finite element method, considering the randomness of fiber spatial distribution and fiber strength. The tensile strength of fiber monofilaments was assumed to follow a statistical two-parameter Weibull distribution. The failure process of UD composite under longitudinal tensile load was simulated by explicit finite element method. The stress–strain curves obtained by simulation are in good agreement with the experimental results. Finally, the influence of different boundary conditions on the calculation of the RVE was studied. It is found that the final failure strengths of the RVE with uniform displacement boundary conditions are similar to the case of periodic boundary conditions, while the former has higher computational efficiency.

Numerical Material Testing of Mineral-Impregnated Carbon Fiber Reinforcement for Concrete.

This work was dedicated to the simulation of fiber composite structures consisting of carbon fibers and mineral impregnation. The aim of this study was to generate a micromodel that predicts the properties of a mineral-impregnated carbon fiber reinforcement. The numerical characterization was based on the discrete microscopic modeling of the individual phases using a representative volume element. In addition, the stochastic nature of the fiber strength, the anisotropic damage mechanisms of the brittle matrix, and the non-linear bonding behavior between the filaments and the matrix were considered in the material models. The material models were adjusted based on the literature sources and our own experimental investigations. This was followed by the validation of the representative volume element, quantifying the evolution of stiffness and damage under longitudinal tensile loading. The numerical results of material stiffness, as well as the tensile strength of the representative volume element, were compared with the results of the experimental investigations. To verify the robustness of the numerical model, significant model parameters were subjected to a sensitivity analysis.

Multi-scale modeling and tensile failure prediction of 3D needled C/C–SiC composites considering real microstructure

Three-dimensional (3D) needled carbon fiber reinforced carbon and silicon carbide (C/C–SiC) composites have the significant advantages of low density, high strength, and long lifespan, which are widely used in aerospace and other industrial fields. In this paper, based on the microstructure of the composites, a multi-scale finite element model is established to predict their mechanical properties and failure behaviors under the tensile load. The multi-scale model has been validated by the static tensile test and the microstructure of fracture. With this model, the effects of the fiber volume fraction, the interfacial bonding strength, the content of residual silicon (Si) elements, and the porosity on the mechanical properties of needled C/C–SiC composites are systematically analyzed. The results show that the stress-strain curve of the composites under the longitudinal tensile load has two nearly linear segments. The final failure strength of the composites increases with the increase of the interfacial bonding strength, the fiber volume fraction and residual Si elements, while decreases with the increase of the porosity. In addition, based on the established multi-scale finite element model, the damage evolution process and failure mechanism of the needled composites are investigated in detail. The proposed scheme could effectively predict the mechanical properties of the needled C/C–SiC composites and capture the microscopic damage evolution, which would help to optimize the design of composites.

The body of a dynamometer wagon for special technical purposes

The development of new and improvement of existing railway rolling stock wagons is an urgent task of our time, providing for cost reduction, both in the process of creation and operation, and in the maintenance of the wagon fleet. The purpose of the work is to modernize the body of a dynamometer wagon for special technical purposes using modeling. To determine the loading of the structural elements of a dynamometer wagon, a calculated three-dimensional model of the wagon body was developed, the reinforcement points of the wagon frame were determined. Compression/tensile strength tests of the wagon were performed on a stand for loading the frames of wagons and elements of coupling devices. The stress-strain state of the wagon structure is determined when statically applied longitudinal test loads are applied to it. The test results and the stress-strain state of the design of the prototype wagon, under the action of statically applied longitudinal compressive and tensile test loads, showed that the proposed design of the wagon meets the established strength requirements, while no visible damage and residual deformations were found in the design of the prototype wagon. The developed design of the dynamometer wagon body can be included in both freight and passenger trains, which solves the problem of efficient and safe use of locomotives when operating trains on mountainous sections of railways of the Republic of Uzbekistan.

Build orientation optimization of additive manufactured parts for better mechanical performance by utilizing the principal stress directions

As Additive Manufacturing technology is excellent for the production of function-based optimized parts. By choosing the right printing orientation, the dimensional accuracy and surface quality of the parts can be improved. But also possible to achieve improvement of the mechanical properties by the proper orientation. An algorithm has been developed, which can determine the optimal build orientation based on a numerical simulation for a given load case. The adverse and favourable load directions can be defined according to the layer's position by knowing the anisotropic behavior of the printed parts. The optimal print orientation has been found for four investigated geometries, according to the No-Preference and Weighted Sum multiple-objective optimization methods, and therefore the expected mechanical performance was increased. The algorithm was able to reduce the amount of unfavourable stresses by 100 % for simple beam geometries with longitudinal tensile and compression loads, while the more complex geometries were improved to the best possible extent.

Effect of Micro- and Macro-Mechanical Characteristics of Jujube Bark on Jujube Girdling Quality

Jujube girdling is an important method to improve the yield and quality of jujube fruit. However, girdling usually causes the tearing of jujube bark, resulting in the slow healing and even death of jujube trees. These problems directly affect the economic benefits of jujube planting. In this paper, in order to reveal the tearing mechanism of jujube bark caused by girdling, and provide the basic mechanical parameters of jujube bark for the research and development of automatic girdling equipment, the structure and mechanical characteristics of jujube bark were studied through theory and experimental methods. The results of microscopic observation showed that jujube bark is a biological composite material mainly composed of the phloem, periderm and epidermis. Furthermore, a mathematical model-based analysis of the growth stress of jujube bark showed that growth stress can be regarded as a biaxial stress state, which can promote the longitudinal tearing of jujube bark during girdling. The tensile test results of jujube bark showed that jujube bark belongs to the category of anisotropic and biologic material. Its longitudinal and transverse mechanical characteristics are significantly different. The maximum longitudinal tensile load was in the range of 105.9~293 N, the longitudinal tensile strength was 16.3 MPa and the elastic modulus was 255.6 MPa. The average transverse tensile load was only 27.9% of the longitudinal tensile load. The transverse tensile strength was 3.5 Mpa and its elastic modulus was 724.14 MPa. The transverse cutting test of jujube bark showed that the average cutting force was 118.2 N and the cutting strength was 9.8 MPa. The results of this study showed that both the growth stress and the anisotropic natural polymer of jujube bark have adverse effects on girdling. Subsequently, issues relating to the selection of appropriate girdling tools and the matters needing attention in the process of the girdling operation were proposed, so as to guide the correct application of girdling technology. In addition, some suggestions on the research and development of girdling tools in the future are put forward.

Stretching Hookean ribbons part II: from buckling instability to far-from-threshold wrinkle pattern.

We address the fully developed wrinkle pattern formed upon stretching a Hookean, rectangular-shaped sheet, when the longitudinal tensile load induces transverse compression that far exceeds the stability threshold of a purely planar deformation. At this "far-from-threshold" parameter regime, which has been the subject of the celebrated Cerda-Mahadevan model (Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), the wrinkle pattern expands throughout the length of the sheet and the characteristic wavelength of undulations is much smaller than its width. Employing Surface Evolver simulations over a range of sheet thicknesses and tensile loads, we elucidate the theoretical underpinnings of the far-from-threshold framework in this setup. We show that the evolution of wrinkles comes in tandem with collapse of transverse compressive stress, rather than vanishing transverse strain (which was hypothesized by Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), such that the stress field approaches asymptotically a compression-free limit, describable by tension field theory. We compute the compression-free stress field by simulating a Hookean sheet that has finite stretching modulus but no bending rigidity, and show that this singular limit encapsulates the geometrical nonlinearity underlying the amplitude-wavelength ratio of wrinkle patterns in physical, highly bendable sheets, even though the actual strains may be so small that the local mechanics is perfectly Hookean. Finally, we revisit the balance of bending and stretching energies that gives rise to a favorable wrinkle wavelength, and study the consequent dependence of the wavelength on the tensile load as well as the thickness and length of the sheet.

Parameterized meso-scale modeling and experimental study on the tensile damage evolution and strength of 3D five-directional braided composites

A parametric finite element model (FEM) of three-dimensional five-directional (3D5d) braided composites was established considering the yarn space contact relationship. By adopting reasonable damage criteria and boundary conditions, the damage behavior and mechanical properties of FEM under tensile loading were investigated. The finite element prediction results are consistent with the experiments, indicating that the FEM can effectively predict the progressive damage and strength of 3D5d braided composites. Damage evolution shows that the main failure modes with small braiding angles include tensile failure of braiding yarn and axial yarn, while the large braiding angles are tensile shear failure of braiding yarn. As the fiber volume fraction increases, the initial damage location of the FEM changes from the intersection of braiding yarn/axial yarn to the junction among the braiding yarns. The stress-strain curves results show that the 3D5d braided composites exhibit brittle fracture characteristics under longitudinal tensile loading, and the mechanical properties are significantly correlated with the braiding angle and fiber volume fraction. In addition, the tensile properties of 3D5d braided composites are also compared with those of three-dimensional four-directional (3D4d) braided composites.

Realizing the impact and compressive strengths of an arrowhead auxetic structure inspired by topology optimization

Auxetic structures have unique properties wherein the structure collapses inward in the lateral direction when compressed longitudinally and expands in the lateral direction when subjected to longitudinal tensile load. This paper focuses on improving the impact absorption potential of the arrowhead auxetic structure. Topology optimization is performed on this structure to identify areas in the structure where material reduction is possible. The optimized structure inspired the creation of three new variants of the arrowhead structure. These designs are 3D printed using ABS and PLA materials. Compression and impact tests are performed on a drop test rig and a compression test set-up. From the results, an optimal design is obtained that strikes a balance between compressive strength and impact absorption. In addition, a scope for functional structures that are tailor-made for specific applications, based on a trade-off between impact absorptivity and compressive strength, is identified.

High-fidelity computational micromechanics of first-fibre failure in unidirectional composites: Deformation mechanisms and stress concentration factors

Stress redistribution and damage phenomena in the vicinity of the first-fibre break in unidirectional composites under longitudinal tensile loads are investigated by means of high-fidelity computational micromechanics based on experimentally characterised material constituents. In this framework, periodic microstructures with statistically representative random fibre packings are analysed, and transient dynamic analyses are performed to take into account the progressive failure and recoiling of a breaking fibre. The effects of mechanisms such as curing residual stresses, fibre/matrix debonding and matrix inelastic deformation on the first-fibre failure process are investigated. The stress concentration factors on intact fibres are found to depend on the statistical failure stress of the breaking fibres, and decrease with increasing strength. For the AS4/8552 composite with average constituent properties, maximum stress concentration factors of 20.6%, 16.1% and 14.2% are predicted, respectively, for fibre volume fractions of 50%, 60%, 70%. Material systems with lower fibre-to-matrix stiffness ratios, such as glass/epoxy, result in lower stress concentration factors. The fibre/matrix interface strength is found to have a limited overall influence on stress redistribution around fibre breakage.

Evaluation of transverse poroelastic mechanics of tendon using osmotic loading and biphasic mixture finite element modeling

Tendon’s viscoelastic behaviors are important to the tissue mechanical function and cellular mechanobiology. When loaded in longitudinal tension, tendons often have a large Poisson’s ratio (ν>2) that exceeds the limit of incompressibility for isotropic material (ν=0.5), indicating that tendon experiences volume loss, inducing poroelastic fluid exudation in the transverse direction. Therefore, transverse poroelasticity is an important contributor to tendon material behavior. Tendon hydraulic permeability which is required to evaluate the fluid flow contribution to viscoelasticity, is mostly unavailable, and where available, varies by several orders of magnitude. In this manuscript, we quantified the transverse poroelastic material parameters of rat tail tendon fascicles by conducting transverse osmotic loading experiments, in both tension and compression. We used a multi-start optimization method to evaluate the parameters using biphasic finite element modeling. Our tendon samples had a transverse hydraulic permeability of 10-4 to 10-5 mm4. (Ns)−1 and showed a significant tension–compression nonlinearity in the transverse direction. Further, using these results, we predict hydraulic permeability during longitudinal (fiber-aligned) tensile loading, and the spatial distribution of fluid flow during osmotic loading. These results reveal novel aspects of tendon mechanics and can be used to study the physiomechanical response of tendon in response to mechanical loading.

An Experimentally and Numerically Comparison between E-Glass/Epoxy and Basalt/Epoxy Pipes Pressurized Internally

The current composite pipes such as E-glass have better properties compared to metallic pipes. However, these pipes are prone to failure during its service life. In contrast, natural fiber such as basalt fiber composite pipes has better mechanical characteristics compared to current composite pipes. Hoop tensile, longitudinal tensile and internal pressure loads were carried out through experimentally and numerically investigation on the basalt/epoxy and E-glass/epoxy pipe performance. The basalt/epoxy and E-glass/epoxy composite pipes have been manufactured with ±55o winding angle using dry filament winding with impregnation of epoxy resin used Vacuum Infusion Process (VIP) technique and investigated. Basalt and E-glass composite pipes with winding angles of ±45o, ±55o, ±65o, ±75o were fabricated in order to assess the optimal winding angle which can resists the subjected loads. There were good agreement between numerical and experimental results have been recorded. For internal pressure test, the basalt pipes have more internal pressure carrying capacity more than E-glass by 2.41%. Through this investigation, can be concluded that the natural based fiber of basalt can be used as a suitable replacement than E-glass, has further advantages of being cheap, abundant, renewable and easily recyclable. The also possess high strength, excellent flexural stiffness to cost ratio and low thermal conductivity

On the influence of a longitudinal tensile load on the deformation of a nonlinear elastic anisotropic body with a crack of normal separation

On the influence of a longitudinal tensile load on the deformation of a nonlinear elastic anisotropic body with a crack of normal separation

Micromechanisms of Cortical Bone Failure Under Different Loading Conditions.

Bone being a hierarchical composite material has a structure varying from macro- to nanoscale. The arrangement of the components of bone material and the bonding between fibers and matrix gives rise to its unique material properties. In this study, the micromechanisms of cortical bone failure were examined under different loading conditions using scanning electron microscopy. The experimental tests were conducted in longitudinal and transverse directions of bone diaphysis under tensile as well as compressive loading. The results show that bone material has maximum stiffness under longitudinal tensile loading, while the strength is higher under transverse compressive loading. A reverse trend of compressive mechanical properties of bone is observed for longitudinal and transverse loading as compared to trends reported in the previous studies. Therefore, micromechanisms of cortical bone failure were analyzed for different loading conditions to reveal such type of behavior of cortical bone and to correlate bone microstructure with mechanical response of bone.

Deformation mechanisms of wood cell walls under tensile loading: a comparative study of compression wood (CW) and normal wood (NW)

Macromolecule deformations of the wood cell wall are of great significance for wood deformation and failure. In this paper, the deformation mechanisms of wood cell walls with different microfibril angles (MFAs) under longitudinal tensile load were investigated by the deformation responses of compression wood (CW) and normal wood (NW). The results indicated that the shift rates of the glucosidic bond and intramolecular hydrogen bond of the cellulose were lower for the CW sample than the NW sample, and no shift was observed in the position of the characteristic peak of the lignin in the spectrum of the CW and NW samples. Under dynamic deformation, the lignin in the wood participated in the stress transfer, and this effect was more pronounced in the CW sample with the larger MFA than the NW sample. In addition, the larger slippage deformation between the cellulose and matrix in the CW resulted in greater deformation of the CW sample than the NW sample. The differences of molecular deformations between CW and NW also could indirectly prove deformation mechanisms of different layers of cell wall, and then wall layer failure under longitudinal tensile stress.

Micro-mechanical analysis of matrix crack-induced delamination in cross-ply laminates in tension

A two-dimensional representative volume element model is developed to study the micro-mechanics of matrix crack-induced delamination in cross-ply laminates under longitudinal tensile loading. Fiber-matrix debonding and matrix cracking are investigated in the 90° ply. The 0° plies are modelled as homogenized, anisotropic elastic solids. A special emphasis is put on the interlaminar region where a thick resin-rich area is explicitly established, and delamination is characterized by a coupled plastic-damage model of the matrix. The process of delamination initiated from the matrix crack tips is accurately revealed by finite element analysis. The impact of different damage mechanisms on the macroscopic mechanical responses is quantitatively captured. A parametric study is done on different cross-ply laminates with various thicknesses of 90° ply to study their effect on the variation of the homogenized longitudinal stiffness and transverse Poisson's responses. It is found that transverse Poisson's response is more sensitive to the damages in the laminate and that degradation of the responses in thicker laminates is severer. In addition, analysis of the influence of thermal residual stress shows that it changes the damage initiation location and evolution path, and affects the transverse Poisson's response more obviously.

Fracture mechanisms of softwood under longitudinal tensile load at the cell wall scale

Abstract This study was undertaken to elucidate the longitudinal tensile fracture behaviors of softwood at the cell wall scale by means of microscopic analyses. The fracture types of the tracheids at the different fracture surfaces were also distinguished. The results indicated that the main tracheid fracture of the earlywood (EW) sample was transverse transwall breakage. The tracheid fracture process of the transverse transwall breakage was initiated as a fracture in the S2 layer, with the crack propagating into the S1/S2 interface. For the EW/latewood (LW) sample, the strain concentration and initial crack under longitudinal tensile load generally occurred in wood rays in the EW part, which caused the tracheids to experience transverse transwall breakage. The differences in longitudinal and transverse strains between EW and LW under longitudinal tensile load led to shear stress and parallel-to-grain cracks occurring at the growth ring border. When the crack propagated along the wood grain in the EW tissue or growth ring boundary, this resulted in EW longitudinal transwall breakage. However, when the crack propagates along the wood grain in the LW tissue, it could cause the LW tracheid to undergo intrawall breakage, with the crack occurring predominantly at the compound middle lamella (CML)/S1 interface region.

Improving the open-hole tension characteristics with variable-axial composite laminates: Optimization, progressive damage modeling and experimental observations

This study consists of a numerical and experimental investigation on unnotched and open-hole tensile characteristics of fiber-steered variable-axial (also known as variable angle-tow and variable-stiffness) composite laminates. The fiber path was obtained from an optimization framework considering manufacturing characteristics of the Tailored Fiber Placement (TFP) process, in which both fiber angle and thickness are locally optimized; besides, unnotched coupons, open-hole samples with unidirectional fibers, fibers along principal stress directions and with optimized fiber path were manufactured and tested under longitudinal tensile loading. The tests were assisted by digital image correlation (DIC) to accurately capture both strain field and failure behavior. A progressive damage model was then developed to simulate the experimental observations. The notched strength-to-weight of the open-hole coupon with an optimized fiber pattern has a notched strength even higher than the unnotched sample. Optical measurements via DIC and numerical predictions evidenced no strain concentrations around the hole near the final failure for coupons with optimized fiber path, where the reinforcing mechanism alleviated the strain concentrations by redistributing the stress uniformly around the coupon.

Analysis of the transverse compressive behavior of Kevlar fibers using microscopic scale approach

During the ballistic impact process of fabrics, yarns are locally subjected to both longitudinal tensile and transverse compressive loading. This paper presents a microscopic numerical investigation of the transverse compressive behavior of a single and bulk aramid fibers. Interactions with friction between single fibers in a yarn have been taken into account. Numerical calculations were performed in the case of a transverse compression using the assumption of plane strain and validated by experimental data. Effects of friction and representative volume size were also discussed. It can be highlighted that using a numerical homogenization technique, the variation of the transverse mechanical effective property versus fiber volume fraction has been determined based on the microscopic transverse behavior of bulk aramid fibers. Finally, power relationships describing effective transverse Young's modulus E¯ and apparent strain ε¯ versus the normalized fiber volume fraction have been proposed and discussed. This effective homogenized material allows the development of homogenized Kevlar yarns and fabrics in the further works of homogenized approaches.