Tensile Direction Research Articles

Interfacial prediction and tensile damage tracking of carbon fiber reinforced polyamide 66 using Z-axis electrical resistance method

Deformation monitoring of the inner fabric is important to ensure the quality of continuous fiber-reinforced composites. A Z-axis electrical resistance (Z-ER) mapping method was utilized as an accurate evaluation method to predict the internal composition and deformation of carbon fiber reinforced polyamide composites (CF/PA) during tensile load. The electrical resistance change rate (ERC) in the tensile direction and the Z-ER for tensile stress were utilized to detect the tensile damage of carbon fiber reinforced polyamide composites. Based on the Z-ER mapping, the internal state of carbon fiber reinforced polyamide composites was categorized into three types: uniform electrical resistance (ER), large standard deviation (SD), and tilt ER. The evaluation method was also able to predict the probability of defective CF/PA exhibiting that the normal tensile failure behavior was approximately 31.5%. This process of detection can be integrated as an in-line evaluation technique to automate and standardize carbon fiber reinforced polyamide composite manufacturing.

Effects of Grain Size, Thickness and Tensile Direction on Yield Behavior of Pure Titanium Sheet

Effects of Grain Size, Thickness and Tensile Direction on Yield Behavior of Pure Titanium Sheet

Influence of anisotropic fiber properties on tensile elastic modulus estimation for carbon fiber reinforced thermoplastics

The influence of anisotropic fiber properties on estimation of the elastic modulus of carbon fiber-reinforced polyamide 6 (CFRPA6) was studied using two kinds of micromechanics models; Nairn et al. and Hashin (N–H) models, and Mori–Tanaka (M–T) model. First, these models’ accuracy was verified by comparison with an elastic modulus measured for injection molded dumbbell specimens of CFRPA6. Although there was a slight difference between the elastic moduli estimated from the N–H models and the M–T model, the difference was discussed in terms of model properties. Next, estimation errors caused by assuming carbon fiber (CF) as isotropic were calculated under several conditions. The maximum error occurred in the condition that the tensile direction was perpendicular to the fiber axis. Despite CF had large anisotropy, it was approximately 10% for both models. We infer that the small error was caused by a specific stress field.

A novel method for generation of particle packing model used in numerical simulation for the mechanical behavior of multi-component material

This study presents a novel algorithm to establish a numerical model for the study of mechanical behavior of multi-component material such as particle reinforced metal matrix composites, concrete, particle filled polymers, etc. The algorithm consists of two steps, one is to divide the given region into sub-regions of a specified size distribution, and the other is to fill each sub-region with particles of specified shapes. During the filling process, the contact states between particles can be controlled by the number and positions of reference points. Taking the quasi-static uniaxial tensile simulation of concrete as a verification example, two concrete models with the same particle size distribution but different shapes have been established. Through the comparison of elastoplastic responses of different aggregate shape models in different tensile directions, it is concluded that the models meet the requirements of macroscopic uniformity, meso-scale randomness and statistical rationality. This verifies the feasibility of modeling method and its advantages in precise control of particle shape, distribution and other parameters.

Parameter identifiability analysis: Mitigating the non-uniqueness issue in the inverse identification of an anisotropic yield function

A large number of conventional mechanical tests are required to calibrate advanced anisotropic yield functions. A well-designed non-conventional mechanical test generating information-rich inhomogeneous strain fields enables to reduce the experimental effort via inverse identification methods. Gradient-based inverse identification methods have repeatedly been reported to yield non-unique solutions for advanced anisotropic yield functions. Although the generic design of non-conventional mechanical tests progressively improves by maximizing the information content using indicators for describing the inhomogeneity of the strain field, it remains questionable whether the uniqueness problem can be avoided for advanced anisotropic yield functions. The latter problem is studied in this paper through the concept of parameter identifiability. A general identifiability analysis framework is proposed enabling to efficiently quantify the parameters sensitivity strength as well as parameter interactions. The feasibility of the framework is assessed through the inverse identification of the Yld2000-2d yield function using a virtual experiment, i.e. a complex notched tensile specimen designed via shape optimization to maximize the strain field inhomogeneity. The advanced synthetic experimentation approach is crucial to avoid errors due to the choice of an inappropriate constitutive model, yet allows accounting for the intrinsic Digital Image Correlation (DIC) filter. For the non-conventional mechanical test under investigation, it is shown that the individual parameter sensitivity and parameter interaction jointly determine the inverse identification quality. It is observed that the detrimental effect of low individual parameter sensitivity on the identification quality can be mitigated by proper parameter subset selection. In addition, it is shown that the orientation of the principal material axes enables to significantly improve the identifiability of the sought model parameters of the anisotropic yield function. The virtual experiment shows that the studied notched tensile test with a tensile direction of 45° from the rolling direction enables to reliably identify all anisotropy parameters of the Yld2000-2d yield function. Finally, actual experiments confirm the importance of identifiability analysis and material orientation for the inverse identification of an anisotropic yield function, yet further research is required to arrive at a sufficiently accurate inverse identification quality.

Intermediate-Temperature Tensile Behavior of a Hot-Rolled Mg-Li-Al-Cd-Zn Alloy.

Developing light structure materials that work stably at elevated temperatures is a long-standing challenge for many application fields, particularly in the development of aerospace equipment. Zn/Cd alloying elements were prospected to improve the stability of the lightest Mg-Li based alloys; however, little is known about the intermediate-temperature mechanical properties of such alloys. The present work investigated the tensile behaviors of a cold-rolled Mg-Li-Al-Cd-Zn alloy in a temperature range of 30–150 °C. The results indicate that the alloy can host a tensile strength σUTS of 108~121 MPa, a yield strength σYP of 97~109 MPa and elongation εB of 14–15 % at 150 °C, dependent on the tensile direction. The mechanical properties intensively are modulated by temperature through the competition between work hardening and softening. Work hardening due to dislocation blocking by the precipitated MgLi2X phase dominated the deformation at low temperatures, while softening that resulted from dynamic recrystallization was the main effect at high temperatures. Correspondingly, a quasi-cleavage mechanism dominated the fracture at temperatures near room temperature, and microvoid coalescence worked at high temperatures above 100 °C. Our results offer a new experimental understanding of the elevated-temperature mechanical behaviors of Mg-Li alloys and will advance the development of new light magnesium alloys with high stability.

Nanoscale in situ observation of damage formation in carbon fiber/epoxy composites under mixed-mode loading using synchrotron radiation X-ray computed tomography

Nanoscale fracture mechanism in CFRPs is still debated owing to the considerable difficulty in determining the three-dimensional mechanism of fracture using conventional techniques such as optical and/or electron microscopy relying on side-surface- and fracture-surface-based observation. In this study, microscopic damages such as fiber/matrix debonding and microcracks under mixed-mode (mode I + II) loading are characterized in situ using nondestructive nanoscopic synchrotron radiation X-ray computed tomography (nanoscopic SR X-CT). It is clearly shown that crack formation proceeds in three steps: (i) initiation at the carbon fiber/epoxy matrix interface, (ii) propagation into the epoxy, and (iii) formation of microcracks (hackles) in the resin matrix, and the resulting microstructures of cracks at the nanoscale are largely affected by the local fiber geometrical distributions. A sharp and straight interfacial crack initiates at the “thin” epoxy-resin region (thickness < half the diameter of the carbon fiber (dCF)) and propagates along the carbon fiber/epoxy interface. The sharp cracks propagate into the epoxy at the “thick” epoxy-region (thickness > ∼1/2 dCF) and hackles are formed in the resin matrix perpendicular to the local principal tensile stress direction. Nanoscopic SR X-CT provides information on three-dimensional mechanisms at the nanoscale during deformation, which is indispensable for understanding heterogenous materials such as CFRPs.

Strain-tuned mechanical, electronic, and optoelectronic properties of two-dimensional transition metal sulfides ZrS2: a first-principles study.

Two-dimensional semiconductor material zirconium disulfide (ZrS2) monolayer is a new promising material with good prospects for nanoscale applications. Recently, a new zirconium disulfide (ZrS2) monolayer with a space group of 59_Pmmn has been successfully predicted. Using first-principles calculations, this new monolayer ZrS2 structure is obtained with stable indirect bandgaps of 0.65eV and 1.46eV at the DFT-PBE (HSE06) functional levels, respectively. Strain engineering studies on the ZrS2 monolayer show effective bandgap modulation. The bandgap shows a nearly linear regularity from narrow to wide under strain (ranged from - 6 to + 8%). Young's modulus of elasticity of ZrS2 along the tensile directions (x-axis and y-axis) is 83.63 (N/m) and 63.61 (N/m) with Poisson's ratios of 0.09 and 0.07, respectively. The results of carrier mobility show that the electron mobility along the y-axis can reach 1.32 × 103 cm2V-1s-1. Besides, the order of magnitude of the light absorption coefficient in the ultraviolet spectral region is calculated to reach 2.0 × 105cm-1 for ZrS2 monolayers. Moreover, the bandgap and band edge position of Pmmn-ZrS2 can satisfy the redox potentials of photocatalytic water splitting by strain regulating. The results indicate that the new two-dimensional Pmmn-ZrS2 monolayer is a potential material for photovoltaic devices and photocatalytic water decomposition.

Enhancing mechanical properties of metallic materials by architecting gradient structures

Here, two types of gradient structures (GS), i.e. gradient dislocation structure (GDS) and gradient grain structure (GGS) are successfully constructed . Results indicate that the relationship between the strength and ductility of the samples with GDS and GGS is referred to as an inverse linear rule, which is in stark contrast to and superior to the banana-shaped strength-ductility trade-off dilemma in monolithic materials. In low-strength (σy ∼400–550 MPa) range, plausible strength-ductility-toughness synergies can be achieved by both the GDS and GGS, however, in high-strength (σy ∼550–750 MPa) range, much better strength-ductility-toughness combinations are presented by the GGS than those by the GDS. For the GGS, the formation of strong 〈110〉 fibre texture in the tensile direction is beneficial for enhancing the high strength-ductility-toughness synergy.

Study on the effects of H on the plastic deformation behavior of grain boundaries in nickel by MD simulation

It is generally believed that the influence of hydrogen on plastic deformation of grain boundaries should be considered when analyzing hydrogen-induced intergranular fracture in polycrystalline metals. In this paper, the equilibrated H distribution around GBs was firstly investigated by employing the grand canonical Monte Carlo method. Then, MD simulations were performed to study the plastic response of GBs under uniaxial tensile loads in different directions, with various bulk H concentrations considered. The results indicate that the influence of H on dislocation nucleation from GB depends on both tensile directions and characteristics of GB structures. Specifically, two dislocation nucleation mechanisms, called dislocation dissociation nucleation (DDN) and heterogeneous dislocation nucleation (HDN), are identified. Careful analyses show that H segregation can increase the energy barrier of DDN, which results in H-inhibited dislocation nucleation. In contrast, the HDN mechanism involves H-enhanced or H-insensitive dislocation nucleation, which mainly depends on the influence of H on GB stress.

Dual-phase morphology distribution effects on mechanical behaviors of Ti6Al4V via pseudorandom crystal plasticity modeling

As an important factor of dual-phase polycrystalline materials, dual-phase morphology distribution significantly affects its deformation mechanism due to the complex biphasic interactions. However, it was rarely investigated, especially for titanium alloy. Although crystal plasticity modeling has been regarded as an important method to study the deformation behaviors, the current models do not fully consider the actual grain scale information of dual-phase materials. In this paper, a pseudorandom dual-phase crystal plasticity finite element (CPFE) model is established, which fully considers the actual grain size and orientation information, volume fraction, and constitutive behaviors of the dual-phase grains. The model is calibrated by uniaxial tensile experiments, and validated from micro and macro levels respectively. Four situations are introduced to study the effects of dual-phase morphology distribution on mechanical behaviors of Ti6Al4V, including Model 1 (dual-phase grains are randomly distributed), Model 2 (dual-phase grains are homogeneously distributed), Model 3 (dual-phase grains are periodically distributed perpendicular to the tensile direction) and Model 4 (dual-phase grains are periodically distributed parallel to the tensile direction). The results show that Model 4 has significant advantages in the comprehensive performance on micro stress/strain homogeneity and macro tensile strength compared with the other three models. Model 2 has the highest tensile strength due to the full use of plugging effect of the phase boundaries on dislocations. The slip transmission between the dual phases is more difficult than that in the hard phase (α phase) due to the different crystal structure. The research results provide a reference for material metallurgy.

Effects of microstructural anisotropy and helium implantation on tensile properties of powder-metallurgy processed tungsten plates

Powder metallurgy (PM)-processed tungsten (W) materials subjected to rolling are being developed for the monoblock divertors of fusion reactors. PM-W exhibits high dislocation density, fine grains, and a layered grain structure, which is introduced by the rolling process. It is expected that its microstructure control will be improved by the brittleness of PM-W at low temperatures. However, it is well known that, in rolled metals, the grain structure depends on the rolling ratio, direction, and temperature. This can cause anisotropy in the mechanical properties. The purpose of this study was to elucidate the effects of microstructural anisotropy and helium (He) implantation on the tensile properties of PM-W plates. The PM-W plates subjected to rolling and stress relief were examined. Miniature tensile specimens were prepared along the following three directions: the tensile directions were parallel to the rolling direction (L.D.), perpendicular to the rolling direction (T.D.), and parallel to the thickness direction (S.D.). The He implantation experiments were performed using a 50 MeV He2+ ion beam of a cyclotron accelerator. The implanted He concentration was approximately 20 appm. Tensile tests were conducted at 100–1100 °C and the ruptured surfaces were observed by scanning electron microscopy. From the results of the as-received condition, microstructural anisotropy was observed in the case of total elongation at temperatures lower than 500 °C. Cracks formed owing to intergranular fracture were observed at the edges of the gauge section along S.D., and anisotropy was observed in the tensile fracture behavior. It is assumed that the cracks tend to propagate along the layers of the grain boundaries. Although the ductility remained almost unchanged along the T.D. after He implantation, a decrease in ductility and brittle fracture were observed along the S.D.. Thus, the effect of He on crack propagation was significant along the S.D..

Microscopic understanding of exceptional orientation-dependent tensile and fracture responses of two-dimensional transition-metal carbides

Two-dimensional (2D) materials have exceptional mechanical properties that are absent in conventional bulk materials due to their ultra-thin structure with ultra-high surface-to-volume ratio. Despite their great potential both for basic research and applications, however, deep understanding of fundamentally important orientation-dependent mechanical responses of 2D materials have rarely been achieved. In this work, for the first time, we investigate the tensile mechanical response of 2D transition-metal carbides (MXenes) as gradually varying tensile direction by using reactive molecular dynamics simulations. Despite its highly bonded multi-atom-thick structure, MXene proves significantly stretchable (11–17%) for all directions with isotropic stiffness desirable for flexible/wearable applications, while exhibiting unusual characteristic fracture anisotropy. Noticeably, these mechanical features remained qualitatively the same regardless of presence/absence of surface termination. We discover that MXene has always fractured into zigzag-atomic edged fragments regardless of tensile direction and/or surface termination. We reveal the detailed fracture mechanism and propose its generalization to other hexagonal 2D materials with validation for both pristine and surface-hydrogenated graphene nanosheets. Based on these findings, we finally present a physically robust, computationally efficient framework for fast and reliable prediction of MXenes’ unique fracture anisotropy, showing excellent agreement with time-consuming simulation results and suggesting broad applicability to 2D material mechanics.

Tensile deformation mechanism of amorphous silicon nitride: Insights from molecular dynamics simulations

The molecular dynamics simulations have been carried out to investigate the mechanical behaviors of amorphous silicon nitride under the uniaxial tensile deformation. The amorphous silicon nitride was obtained by the cooling process. The network structure of the sample consists of SiNx (x = 3, 4 and 5) units and NSiy (y = 2, 3 and 4) linkages. The stress-strain curve of the sample exhibits the elastic and plastic deformation. The Si-N bond lengths are stretched out in the elastic region and the plastic region I. They are shrunk to the initial state in the plastic region II due to the appearance of the large clusters which contain the overlapping big simplexes with the RS ≥ 2.4 Å. These big simplexes tend to appear at the shear transformation zones in the elastic region. These shear transformation zones tend to form the shear band inclined 45° with the tensile direction. The big simplexes grow and coalesce along the shear band in the plastic region I. In the plastic region II, the clusters of big simplexes grow in the shear band, causing the crack propagation across the sample.

Nondestructive Photoelastic and Machine Learning Characterization of Surface Cracks and Prediction of Weibull Parameters for Photovoltaic Silicon Wafers

Abstract A nondestructive photoelastic method is presented for characterizing surface microcracks in monocrystalline silicon wafers, calculating the strength of the wafers, and predicting Weibull parameters under various loading conditions. Defects are first classified through thickness infrared photoelastic images using a support vector machine-learning algorithm. Characteristic wafer strength is shown to vary with the angle of applied uniaxial tensile load, showing greater strength when loaded perpendicular to the wire speed direction than when loaded along the wire speed direction. Observed variations in characteristic strength and Weibull shape modulus with applied tensile loading direction stem from the distribution of crack orientations and the bulk stress field acting on the microcracks. Using this method, it is possible to improve manufacturing processes for silicon wafers by rapidly, accurately, and nondestructively characterizing large batches in an automated way.

Modeling the Hydrogen Redistribution at the Grain Boundary of Misoriented Bicrystals in Austenite Stainless Steel.

Hydrogen embrittlement, as one of the major concerns for austenitic stainless steel, is closely linked to the diffusion of hydrogen through the grain boundary of materials. The phenomenon is still not well understood yet, especially the full interaction between hydrogen diffusion and the misorientation of the grains. This work aimed at the development of a robust numerical strategy to model the full coupling of the hydrogen diffusion and the anisotropic behavior of crystals in 316 stainless steel. A constitutive model, which allows easy incorporation of crystal orientation, various loading conditions, and arbitrary model geometries, was established by using the finite element package ABAQUS. The study focuses on three different bicrystal models composed of misoriented crystals, and the results indicate that the redistribution of hydrogen is significant closely to the grain boundary, and the redistribution is driven by the hydrostatic pressure caused by the misorientation of two neighboring grains. A higher elastic modulus ratio along the tensile direction will lead to a higher hydrogen concentration difference in the two grains equidistant from the grain boundary. The hydrogen concentration shows a high value in the crystal along the direction with stiff elastic modulus. Moreover, there exists a large hydrogen concentration gradient in a narrow region very close to the grain boundary to balance the concentration difference of the neighboring grains.

Mechanical Behavior of Reactive Powder Concrete Subjected to Biaxial Loading

To investigate the biaxial mechanical characteristics of reactive powder concrete (RPC), RPC plate specimens and bone‐shaped specimens were tested under compression‐compression and compression‐tension loadings, respectively. The strengths and strains of the specimens were recorded, and the crack patterns and failure modes in various stress states were examined. Based on the test data, the characteristics of biaxial strength were analyzed, and a biaxial failure criterion was established. The characteristics of major stress‐strain curves and failure modes in different biaxial stress states were determined. The results show that the ratio between the biaxial compression strength and the uniaxial compression strength was 1.44–1.58 for RPC. When the stress ratio under compression‐tension was −0.05, the tensile strength decreased by 48%. Under compression‐compression, the proportional limit of RPC was about 95%, and its peak strain was high. Under compression‐tension, as the compressive stress increased, the elastic modulus decreased, and the peak strain in the tensile direction increased. When the RPC specimens were under compression‐compression, the failure mode of RPC was splitting failure. Under compression‐tension, the failure mode changed from single‐crack tensile failure to multicrack compressive failure with increasing confining stress.

Mechanical characterization of 3D-printed silicone/epoxy hybrids

A new family of materials made of chemically compatible silicone/epoxy hybrids was recently reported. By tuning the silicone/epoxy ratios, the elasticity of the hybrid could be finely tuned over five orders of magnitude. Processable by direct ink writing (DIW), an extrusion-based additive manufacturing technology, these materials displayed high interfacial toughness between different phases. In this study, the impact of two key parameters on the mechanical characterization of these hybrids was studied. First, the impact of reducing the tensile test specimen by a factor 3 from established ASTM standards was analyzed. It was found that reducing the sample dimensions does not significantly alter the mechanical properties, even though higher standard deviations were observed in the range of 5 to 15%, in particular for stiffer samples. Second, the impact of printing orientation was studied by comparing samples printed longitudinally and transversally to the tensile direction. Longitudinally printed samples exhibited higher stiffness properties of about 15% to 35% than transversally printed specimens (higher elastic modulus, lower elongation at break), while values between longitudinally printed and cast samples with same dimensions were comparable. These results show the possibility to reduce the sample dimensions when savings in processing time, costs, or materials are required, while processing materials by DIW impacts the mechanical properties.

AE Monitoring of Damage in Flexible Solar Cells under Biaxial Loading

Microdamage initiation and accumulation processes in flexible solar cells under biaxial tensile loading were monitored by acoustic emission (AE) technique. Furthermore, the contribution to the degradation of power generation performance was evaluated using lock-in thermography (LT). Comparing the results of uniaxial with biaxial tensile tests, it was shown that the strains at the onset of the degradation in the maximum power Pmax and the short circuit current Isc were equivalent for both tests. Whereas the open circuit voltage Voc decreased at lower strain in the biaxial test than the uniaxial. Furthermore, it was also observed that the cracks near the current collection holes were perpendicular to the tensile direction in the uniaxial, whereas in the biaxial, the cracks were radial from the current collection holes. Consequently, the fundamental knowledge on the characterization of durability of flexible solar cells, such as the prediction of degradation was obtained.

New Simulation Method for Metallographic Changes of Single Crystal Ni Based Superalloys for Gas Turbine Blades in High Temperature Creep Regions via Discrete Cosine Transform incorporated into Maximum Entropy Method

Single crystal Ni based superalloys for Gas Turbine blades has an interesting structure that the L12 γ' phase cubes are regularly arranged at equal intervals in the face center cubic γ phase. During the high temperature creep test, the γ' phase of Ni based superalloys has multiple cubes in the transition region. However, the γ' cubes begin to connect with one another in the lateral direction perpendicular to the tensile direction to be rafting structures in the steady state region and the accelerating region. The multi scale simulation methods including the three dimensional phase field method are well-known as simulation methods for phase changes. However, it is convenient to have a simulation method for metallographic changes using various metallographic charts in published papers and data bases, because the published metallographic charts can be utilized for prediction of the behavior between the charts before and after phase transition. Therefore, in this research, Metallographic changes of CMSX-4 which is a single crystal Ni based superalloy in the accelerating region were studied by using metallographic charts of Miura, Kondo and Matsuo's paper via the two dimensional discrete cosine transform (2D-DCT) and the Maximum Entropy Method. As a result, it has been found out that this method could be a promising method to study metallographic changes coming up with the creep rate changes.