Experimental Tensile Tests Research Articles

Experimental and Numerical Evaluation of Mechanical Properties for Carbon Fiber Reinforced Epoxy LY5052 Composite for Prosthesis Structures

Carbon Fiber Reinforced Epoxy is a material that is widely used in the manufacture of prosthesis structures. In this research, the carbon fiber used is plain weave-type carbon, while the matrix used is LY5052 epoxy, LY5052 epoxy has advantages such as low viscosity and long pot life making it possible to manufacture large-sized prostheses. The first step in this research is making specimens using the vacuum infusion method and then cutting the specimens with dimensions referring to ASTM D3039. Furthermore, tensile test experiments were carried out with the results obtained that the maximum stress () was 537.15 MPa. As an evaluation, a tensile test simulation was carried out with Finite element analysis using Abaqus software, the material properties used were the results of a tensile test experiment, in the process the mesh selection was carried out by input sizing control many times this was done to determine the accuracy of the results. The tensile test simulation results with abaqus software are 523.3 MPa when compared to the experimental, the difference is only 2.58%. based on experimental and simulation results, the mechanical properties of the Carbon Fiber Reinforced Epoxy LY5052 Composite material are almost the same, so that in the manufacture of prosthesis the mechanical properties data in this study can be used when performing numerical analysis in the prosthesis design process.

Mechanical Properties Decay of Corroded Reinforcement in Concrete—An Overview

Among the leading consequences of corrosion in reinforced concrete structures (RCS) the cross section reduction in steel bars should be mentioned, coupled to a decay of their mechanical material properties. This paper recalls the main literature findings on the topic and describes a wide collected database of experimental tensile tests performed on naturally corroded reinforcements. The principal predictive degradation laws available in the scientific literature to assess the residual mechanical properties of the corroded reinforcements are synthesized. A first attempt to evaluate the reliability of the literature decay laws to simulate the mechanical performance of naturally corroded steel reinforcement subjected to both uniform and pitting corrosion is performed. Finally, some remarks are suggested on both the tested naturally corroded steel reinforcement and the available degradation laws.

Study on Nitrile Oxide for Low-Temperature Curing of Liquid Polybutadiene.

As a significant component of composite solid propellants, the cross-link alkenyl polymers need to cure at high temperatures and the current isocyanate curing systems are highly humidity sensitive. This paper presented a low-temperature curing method for a cross-linked polymer (polybutadiene) with stable wettability by using cycloaddition of the nitrile oxide of tetramethyl-terephthalobisnitrile oxide (TTNO) and the C=C group of liquid polybutadiene (PB). The TTNO was synthesized in four steps from 1,2,4,5-tetramethylbenzene and evaluated as a low-temperature hardener for curing liquid PB. To characterize the reaction ability of TTNO at 25 °C, the cross-linked rubber materials of various contents (8%, 10%, 12%, 14%, 16%) of curing agent TTNO were prepared. The feasibility of the curing method can be proved by the disappearance of the absorption peak of the nitrile oxide group (2300 cm−1) by FT-IR analysis. Contact angle, TG-DTA and tensile-test experiments were conducted to characterize the wettability, thermo-stability and mechanical properties of the obtained cross-linked rubber materials, respectively. The results showed that the curing agent TTNO could cure PB at room temperature. With the growing content of the curing agent TTNO, the tensile strength of the obtained cross-linked rubber material increased by 260% and the contact angle increased from 75.29° to 89.44°. Moreover, the thermo-stability performances of the cross-linked rubber materials have proved to be very stable, even at a temperature of 300 °C, by TGA analysis.

Static and Fatigue Behaviour of Double-Lap Adhesive Joints and Notched Metal Samples Reinforced by Composite Overlays.

The use of composite overlays to increase the fatigue life of notched steel samples is discussed in this paper. For such purposes, in the first set of studies, static and fatigue tests as well as the detailed analytical and numerical analyses for samples with double-lap joints were performed. Based on such studies, the shapes of the composite overlays were set. For a better understanding of the failure forms of the investigated adhesive joints, the experimental studies were monitored with the use of digital image correlation. In the second set of experimental studies, the static and fatigue tensile tests were performed for steel samples with a rectangular opening with rounded corners reinforced by composite overlays. The different shapes (square 45 × 45 mm and long stripes 180 × 15 mm) and composite materials (GFRP and CFRP) were used as overlays. The obtained improvement of fatigue life was in the range of 180–270% in the case of the rectangular overlays and 710% in the case of application of the overlays in the form of the long stripes. This was also confirmed by numerical analyses in which a reduction in the stress concentration factor from 2.508 (bare sample) through 2.014–2.183 (square 45 × 45 mm overlays) to 1.366 (overlays in the form of long stripes 180 × 15 mm) was observed.

Mechanical Properties of the Stereolithography Resin with Different Printing Configurations.

In the 3D printer market, there are several types of printing; among those found in the middle are fused filament deposition printing and stereolithography. In stereolithography, layers of resin are solidified employing UV rays. Each manufacturer offers different types of resins that react to light exposure. These usually have very general values in terms of their mechanical strength, with varying properties depending on the printing configurations. For this reason, the user, in many cases, must make trial and error prints to obtain the best possible printing configuration, generating expenses and waste of material. This research proposes establishing the appropriate printing parameters to obtain the best mechanical properties of the prototypes printed in the digital light process stereolithography printer of the Universidad Tecnica del Norte. A specimen fabrication process based on the ASTM D638 standard is established, in which the main printing configurations are varied, such as printing orientation, layer thickness, and light exposure time. Experimental tensile tests obtain deformation stress-strain curves. From this, the behavior of the printed material is obtained as linear elastic-fragile. The results obtained are compared concerning the maximum stress and strain, and the modulus of elasticity is calculated. The most suitable printing parameters are proposed to obtain the best results in stereolithography printing for the construction of functional prototypes.

Systematic Approach for Finite Element Analysis of Thermoplastic Impregnated 3D Filament Winding Structures—Advancements and Validation

This work aims to enhance and validate a systematic approach for the structural finite element (FE) analysis of thermoplastic impregnated 3D filament winding structures (fiber skeletons). The idealized modeling of geometrically complex fiber skeletons used in previous publications is refined by considering additional characteristic dimensions and investigating their mechanical influence. Moreover, the modeling approach is transferred from the meso- to the macro-level in order to reduce modeling and computational effort. The properties of meso- and macro-level FE models are compared using the example of simple loop specimens. Based on the results, respective application fields are defined. In the next step, the same modeling approach is applied to a more complex, three-dimensional specimen—the inclined loop. For its macro-level FE model, additional material characterization and modeling, as well as enhancements in the modeling of the geometry, are proposed. Together with previously determined effective composite properties of fiber skeletons, these results are validated in experimental tensile tests on inclined loop specimens.

Effect of Fiber Type and Content on Mechanical Property and Lapping Machinability of Fiber-Reinforced Polyetheretherketone.

Polyetheretherketone (PEEK) is a novel polymer material with excellent material properties. The hardness and strength of PEEK can be further improved by introducing fiber reinforcements to meet the high-performance index of the aerospace industry. The machinability will be influenced when the material properties change. Therefore, it is crucial to investigate the influence of material properties of the fiber-reinforced PEEK on machinability. In this paper, the main materials include pure PEEK, short carbon-fiber-reinforced PEEK (CF/PEEK), and short glass-fiber-reinforced PEEK (GF/PEEK). The effects of the fiber type and mass fraction on the tensile strength, hardness, and elastic modulus of materials were discussed using the tensile test and nanoindentation experiments. Furthermore, the fiber-reinforced PEEK lapping machinability was investigated using lapping experiments with abrasive papers of different mesh sizes. The results showed that the hardness and elastic modulus of PEEK could be improved with fiber mass fraction, and the tensile strength of CF/PEEK can be improved compared with that of GF/PEEK. In terms of lapping ability, the material removal rates of the fiber-reinforced materials were found to be lower than the pure PEEK due to the higher hardness of the fiber. During the lapping process, the material removal methods mainly included the ductile deformation or desquamation of reinforcing fiber and ductile removal of the PEEK matrix. The lapped surface roughness of PEEK material can be improved by fiber reinforcement.

Effect of agglomeration and dispersion on the elastic properties of polymer nanocomposites: A Monte Carlo finite element analysis

Abstract Owing to their superior mechanical and physical properties, carbon nanotubes (CNT) seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. In most of the experimental results up to date, however, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. In the present paper, the influence of single wall carbon nanotube agglomeration on the effective stiffness is analyzed by using an Eshelby’s inclusion model. Analytical expressions are derived for the effective elastic stiffness of single wall carbon nanotubereinforced composites with the effects of agglomeration. The present study not only provides the important relationship between the effective properties and the morphology of CNT-reinforced composites, but also may be useful for improving and tailoring their mechanical properties. In addition, a multiscale Monte Carlo finite element method (MCFEM) was used for determining mechanical properties of polymer nanocomposites (PNC) that consist of polymers reinforced with single-walled carbon nanotubes (SWCNT). Specifically, the method uses a multiscale homogenization approach to link the structural variability at the nano/micro scales with the local constitutive behavior. Subsequently, the method incorporates a FE scheme to determine the Young’s modulus and Poisson ratio of PNC. The use of the computed properties in macroscale modeling is validated by comparison with experimental tensile test data.

Experimental investigation of the effects of aging and cryogenic treatments on the mechanical properties of superelastic nickel-titanium shape-memory alloys

In this study, electropolishing and two different heat treatments were applied to wires made of superelastic nickel-titanium (NiTi) shape-memory alloy (SMA) and their mechanical properties and stress-induced deformations were investigated. In experimental studies, cryogenic and aging heat treatments were applied to NiTi SMA wire samples and tensile test experiments were carried out to determine the effect of the heat treatments on their mechanical properties. Following the tensile test experiments conducted at room temperature (23°C), the study investigated changes in the elemental composition, fracture modes, micro cracks, and phase structures and in the mechanical properties formed in the fracture region. Intermetallic phase structures (Ti2Ni, Ni3Ti, and Ni4Ti3) were observed in the X-ray diffraction (XRD) analyses. It was concluded that the aging heat treatment had directly affected the reduction in hardness. In particular, in samples without the aging heat treatment, a stress-induced decrease in the Ni and Ti ratios and an increase in the carbon (C) ratio were observed in the chemical composition of the fracture surface of the superelastic NiTi SMA wires. It was determined that the changes in the chemical composition caused by stress had affected the mechanical properties negatively. In the fractography of the NiTi SMA wires, the samples exhibited mostly ductile fracture behavior with small dimples.

Crystal Plasticity Modeling of Grey Cast Irons under Tension, Compression and Fatigue Loadings

The study of the micromechanical performance of materials is important in explaining their macrostructural behavior, such as fracture and fatigue. This paper is aimed, among other things, at reducing the deficiency of microstructural models of grey cast irons in the literature. For this purpose, a numerical modeling approach based on the crystal plasticity (CP) theory is used. Both synthetic models and models based on scanning electron microscope (SEM) electron backscatter diffraction (EBSD) imaging finite element are utilized. For the metal phase, a CP model for body-centered cubic (BCC) crystals is adopted. A cleavage damage model is introduced as a strain-like variable; it accounts for crack closure in a smeared manner as the load reverses, which is especially important for fatigue modeling. A temperature dependence is included in some material parameters. The graphite phase is modeled using the CP model for hexagonal close-packed (HCP) crystal and has a significant difference in tensile and compressive behavior, which determines a similar macro-level behavior for cast iron. The numerical simulation results are compared with experimental tensile and compression tests at different temperatures, as well as with fatigue experiments. The comparison revealed a good performance of the modeling approach.

Cell-Laden Alginate Hydrogel Modelling using Three-Dimensional (3D) Microscale Finite Element Technique

A novel modelling technique using finite element analysis to mimic the mechanoresponse of cell-laden biomaterial is proposed for the use in bioinks and other tissue engineering applications. Here, a hydrogel-based composite biomaterial specimen was used consisting of 5% (V/V) HeLa cells added to alginate solution (4% W/V) and another specimen with no living cell present in alginate solution (4% W/V). Tensile test experiments were performed on both the specimens with a load cell of 25 N. The specimens were bioprinted using an in-house developed three-dimensional (3D) bioprinter. To allow for the nonlinear hyperelastic behaviour of the specimen, the specimens were loaded very slowly, at rates of 0.1 mm/min and 0.5 mm/min, during the tensile test, respectively. The microscale finite element models developed in ANSYS were loaded with similar load rates and their responses were recorded. Both the model results were validated with the experiment results. A very good agreement between the finite element model and the tensile test experiment was observed under the same mechanical stimuli. Hence, the study reveals that cell-seeded bioprinted scaffold can be virtually modelled to obtain its mechanical characteristics beforehand.

An insight into the mechanical behavior of adhesively bonded plain-woven-composite joints using multiscale modeling

The mechanical behavior of adhesively bonded plain-woven-composite (PWC) joints has been investigated using a multiscale modeling approach. Microscale and mesoscale representative volume elements (RVEs) have been constructed using the hierarchical architectures of PWCs. Based on the local homogenization of the mesoscale RVE model, an equivalent cross-ply laminate (ECPL) cell is developed to represent the woven architecture. It enables not only to accurately compute the effective properties of PWCs, but also to efficiently retain the local behavior within each ply. The macroscale models of single-lap joints (SLJs) and double-lap joints (DLJs) fabricated with PWCs, are constructed by topologically arraying the ECPL cells. Combined with continuum damage mechanics (CDM) and cohesive zone model, the mechanical behaviors are predicted for the SLJs and DLJs subjected to tensile loads. Moreover, experimental tensile tests have been performed on the corresponding SLJ structures, which confirm the reliability of the proposed multiscale models. A parametric study of the overlap length and width, as well as the bondline thickness has been numerically carried out to further analyze their effect on the joining performance. It reveals that, the dominant damage mechanisms mainly depend on the overlap length. When the overlap length is less than a critical value, the main damage mode is identified as the debonding of the bondlines. Otherwise, the delamination and matrix-tensile damages within the composite adherends are considered as the dominant damage modes.

Failure criteria assessment of carbon/epoxy laminate under tensile loads using finite element method: Validation with experimental tests and fractographic analysis

The failure of polymer composites is complex due to the independent and interacting damage mechanisms. The availability of several failure criteria demands a reasonable discernment of each criterion in order to obtain a consistent response to make an assertive selection. The importance of this decision is present in simulation works using finite element method and it is of particular interest of the industry and designers, once an optimized project is the goal. This study regards a carbon/epoxy laminate based on plain weave fabric subjected to tensile load and numerical simulations using finite element method was applied to compare the widely used Maximum Stress, Tsai-Wu, Hoffman, Tsai-Hill, Hashin and Puck failure criteria. Experimental tensile tests were carried out and fractographic analysis was performed in order to validate the finite element model and the applicability of the failure criteria. The model presented a good agreement with the experimental results and the correlation between the fractographic analysis and the failure criteria results allowed to select the Puck criterion as the proper and adequate for the studied composite laminate subjected to tensile load.

Biomechanics of skin grafts: effect of pattern size, spacing and orientation

Skin graft expansion is the key to the treatment of severe burn injuries requiring skin transplantation. While high expansions have been claimed by a majority of graft manufacturers, the realistic expansions reported to date with skin grafts are much lower. To clarify this discrepancy, we attempted to understand the biomechanics of skin grafts through the study of common graft pattern sizes, spacing, and orientation, and their influence on mesh expansion and induced stress. A novel skin simulant material and additive manufacturing were employed to develop the skin graft models. Tensile testing experiments were conducted to study expansion and overall stresses, and a finite element model (FEM) was used to characterize the local trends. At low strains (i.e., <1), the mesh expansion ratio was reported to be below 1, which increased up to 1.93 at a high strain of 2. The pattern size and spacing were not observed to affect the expansion much (i.e., <10%). With a change in orientation, the expansion decreased across all graft models and strains. High localized induced stresses were reported for high strains, which varied with graft orientation. The novel observations highlight the achievable expansions without overstressing, with standard slit patterning in skin grafts. These findings will not only help achieve better mesh expansion outcomes in burn surgeries but also guide the development of novel graft patterns for enhanced expansion in the future.

Numerical homogenization of a linearly elastic honeycomb lattice structure and comparison with analytical and experimental results

This paper presents a verification and validation analysis of Finite Element (FE) models predicting the mechanical response of linearly elastic honeycomb structures. We have studied three main models, namely: analytical models based on beam theories, explicit FE models where the cell geometry is explicitly meshed with 3D elements, and numerical homogenized FE models where a plate made of a honeycomb structure is meshed with 2D elements whose mechanical properties were predicted from numerical homogenization. We compared the predictions of these simulations against experimental uni-axial tensile tests where we mechanically tested 3D printed honeycomb specimens having a relative density of 40% and made of 13 and 37 cells, respectively. Comparison of the experimentally measured axial stiffness to the numerical predictions revealed that the numerical homogenization models can predict the apparent in-plane stiffness in structures made of 37 cells within 4%, while the discrepancy increases to 70% when 13 cells are considered. To quantify this discrepancy, we also provided a relationship between the number of represented cells and the discrepancy of the numerical homogenized model against the explicit FE models to predict the in-plane stiffness. We believe that these results could be important for the application of the homogenized models in optimization of honeycomb lattice structures whose relative density varies with space.

Finite element modeling of the complex anisotropic mechanical behavior of the human sclera and pia mater

Background and objectiveAccurate finite element (FE) simulation of the optic nerve head (ONH) depends on accurate mechanical properties of the load-bearing tissues. The peripapillary sclera in the ONH exhibits a depth-dependent, anisotropic, heterogeneous collagen fiber distribution. This study proposes a novel cable-in-solid modeling approach that mimics heterogeneous anisotropic collagen fiber distribution, validates the approach against published experimental biaxial tensile tests of scleral patches, and demonstrates its effectiveness in a complex model of the posterior human eye and ONH. MethodsA computational pipeline was developed that defines control points in the sclera and pia mater, distributes the depth-dependent circumferential, radial, and isotropic cable elements in the sclera and pia in a pattern that mimics collagen fiber orientation, and couples the cable elements and solid matrix using a mesh-free penalty-based cable-in-solid algorithm. A parameter study was performed on a model of a human scleral patch subjected to biaxial deformation, and computational results were matched to published experimental data. The new approach was incorporated into a previously published eye-specific model to test the method; results were then interpreted in relation to the collagen fibers’ (cable elements) role in the resultant ONH deformations, stresses, and strains. ResultsResults show that the cable-in-solid approach can mimic the full range of scleral mechanical behavior measured experimentally. Disregarding the collagen fibers/cable elements in the posterior eye model resulted in ∼20–60% greater tensile and shear stresses and strains, and ∼30% larger posterior deformations in the lamina cribrosa and peripapillary sclera. ConclusionsThe cable-in-solid approach can easily be implemented into commercial FE packages to simulate the heterogeneous and anisotropic mechanical properties of collagenous biological tissues.

Effect of Two-Stage Aging on Microstructure and Properties of Al-Mg-Si Alloys

The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

Calculation methodology of additive manufacturing processed parts

Additive manufacturing technologies allow us the creation of 3D objects through layer overlay. This process is faster than other traditional manufacturing processes and it enables the customization of parts. Nowadays Fused Deposition Modelling (FDM) is the most used techonology. However, due to the nature of the process, resulting parts have complex mechanical behaviour, due to the fact that their properties vary according to the direction or the type of effort, which limits their applications in functional parts. To predict the behavior of a component Finite Element Analysis (FEA) are made. Although, the material models used by these analysis tools are not able to simulate the mechanical behavior of FDM products. Thus, a model supported by a finite element analysis tool, able to predict the behaviour of these materials has been developed. It works in the elastic and plastic region, for any geometry and load case. The model, feed by theoretical behavior models and experimental tensile, compression and shear tests, and implemented in FEA software, allows us to simulate the anisotropy of these materials in an easy and versatile way. The calculation methodology has also been experimentally validated.

Effect of grain refiner, modifier and graphene on the mechanical properties of hyper eutectic Al-Si alloys by experimental and numerical investigation

The present work focuses on the study of mechanical properties of die cast hypereutectic Al-16Si alloys that are subjected to grain refinement and modification. It further deals with the study of the influence of the reinforcement of graphene to the sample that is simultaneously grain refined and modified. Hyper eutectic Al-16Si alloys are die casted with five different compositions. The Vickers hardness test and tensile strength test are performed on the all the casted samples. The Optical microstructure examination of the specimens is performed. The numerical simulation data derived from finite element analysis of the tensile test is validated against experimental tensile test results and both were found to coincide. Using experimental data, two alternative constitutive models, namely the modified Johnson Cook (m-JC) model and the integrated JC-ZA model, were formulated on the investigated materials for precise flow stress behaviour prediction. The JC-ZA model's integration is expected to improve prediction power in relevant consideration conditions.

Optimisation of numerical models of welded joints with multiple defect combinations

This paper presents the continued efforts in investigating behaviour of low-alloyed low-carbon steel welded joints in the presence of different combinations of multiple welding defects, (undercuts, incomplete root penetration, misalignments). Since these defect combinations can greatly affect the integrity of welded joints, due to significant changes in geometry which are induced by their presence. For this reason, a total of 8 numerical models were made, including four different defect combinations (2 models for each group). This number of models was equal to the number of actual test specimens that were used for tensile test experiments, which also provided the necessary input data (mechanical properties) for each model. The goal was to determine if the two models from each group were sufficiently similar to each other, so that in the future research, they could be replaced by a single, unified model for each defect combination. Comparison was made in terms of stress and strain distribution, and it was determined that three out of four models have nearly identical values, whereas the first group specimens had shown slightly bigger differences, which were still acceptable. Thus, it was concluded that a single representative model could be made for each defect combination group.