Tensile Failure Behavior Research Articles

Characterization and Simulation of Nanoscale Catastrophic Failure of Metal/Ceramic Interfaces.

The catastrophic failure of metal/ceramic interfaces is a complex process involving the energy transfer between accumulated elastic strain energy and many types of energy dissipation. To quantify the contribution of bulk and interface cohesive energy to the interface cleavage fracture without global plastic deformation, we characterized the quasi-static fracture process of both coherent and semi-coherent fcc-metal/MgO(001) interface systems using a spring series model and molecular static simulations. Our results show that the theoretical catastrophe point and spring-back length by the spring series model are basically consistent with the simulation results of the coherent interface systems. For defect interfaces with misfit dislocations, atomistic simulations revealed an obvious interface weakening effect in terms of reduced tensile strength and work of adhesion. As the model thickness increases, the tensile failure behaviors show significant scale effects-thick models tend to catastrophic failure with abrupt stress drop and obvious spring-back phenomenon. This work provides insight into the origin of catastrophic failure at metal/ceramic interfaces, which highlights a pathway by combining the material and structure design to improve the reliability of layered metal-ceramic composites.

Support design of overhanging structure for laser powder bed fusion

Warpage deformation inevitably occurs when laser powder bed fusion (LPBF) is applied on an overhanging structure. An effective support added to the system can mitigate warpage and improve the accuracy of formed parts. Four types of support structures are designed, and sheet tensile specimens and overhanging structures with different support structures are fabricated in this study. The tensile failure behavior and warpage suppression ability of different support structures are investigated, with the relation of the support influence to the design of support structure analyzed. The results show that the support with reinforcement can effectively restrain warpage deformation of the overhanging structure. During the process of tension, the main failure area of the support structure is located on the top of the support structure, close to the overhanging solid body. Increasing the change ratio of the support cross-sectional area is helpful to improve the constraint ability of the support. This design provides a new method for accurate forming of overhanging structures via LPBF and evaluating the restrain ability of support structures.

Tensile Failure Behaviors and Theories of Carbon/Glass Hybrid Interlayer and Intralayer Composites

Hybrid composites combine various types of fiber that not only provide an effective method to minimize material costs but also enhance the mechanical properties of composites. The tensile fracture behaviors of hybrid composites are more complex than single-fiber composites due to various reinforcing fibers and hybrid effects, and the relationship between tensile behaviors and hybrid structures is not clear. In this paper, various structures of C/G (carbon/glass) interlayer and intralayer hybrid composites were designed, and tensile behaviors were investigated; it revealed that tensile failure is characterized by the synergistic effect and failure acceleration effect. Second, the tensile properties of interlayer and intralayer hybrid composites with various hybrid ratios and stacking structures were systematically analyzed; our results demonstrated that the tensile strength of interlayer and intralayer hybrid composites was predominantly impacted by the hybrid ratio of C/G and increased with the increase in carbon fiber content. For interlayer hybrid composites, with the assistance of the synergistic effect, excellent tensile strength could be obtained for the glass fiber sandwiched carbon fiber structure. For intralayer hybrid composites, the tensile strength was small, while the dispersion degree was high. We compared the tensile properties with theoretically calculated values based on the rule of mixing (ROM) and revealed that the tensile modulus and strength of interlayer and intralayer hybrid composites exhibited a positive hybrid effect. This work serves as a foundation for the structural optimization and potential applications of C/G non-crimp hybrid composites.

The effect of temperature on the tensile properties and failure mechanisms of two-dimensional braided composites

Abstract Two-dimensional (2D) braided composites have excellent structural integrity and damage tolerance. Currently, there are few researches focused on the effect of temperature on tensile failure behaviors of 2D braided composites. In this study, 2D biaxial braided composites with different fiber materials were prepared, and the tensile properties and failure mechanisms of these braided composites at different temperatures were studied by means of the tensile test and the high-definition charge coupled device optical microscope. The results show that temperature has significant effects on the tensile properties and fracture damage of 2D braided composites. As the temperature increases, the tensile properties of the two braided composites decrease obviously, and their external fracture failure becomes subtle, while their internal deformation damage becomes significant. Moreover, the differences between the two fibers in tensile fracture behaviors of composites can be more conspicuously observed at higher temperatures.

Tensile mechanical properties and fracture evolution characteristics of sandstone containing parallel pre-cracks under dynamic loading

Parallel cracks have a significant influence on the dynamic tensile failure behavior of rock. The systematic investigation of dynamic tensile mechanical properties and fracture evolution characteristics of fractured rocks are significant for guiding the safe excavation and stability sustaining of rock engineering. Two groups of dynamic Brazilian splitting tests were conducted for the sandstone specimens containing parallel pre-cracks. The influences of crack inclination angle (Group A) and rock bridge length (Group B) on the tensile mechanical properties and fracture evolution characteristics were analyzed. Results showed: the dynamic peak load of pre-cracked specimens is significantly lower than that of intact specimens. The peak load presents a V-shaped evolution trend with the growth of crack inclination angle. Differently, the dynamic peak load increased monotonically with the increasing of rock bridge length. In addition, the crack initiation points move from crack tips to crack walls when the crack inclination angle is increasing. When rock bridge length is large enough, the crack propagation paths are observed near the central axis of specimens. By utilizing the DIC method, six different failure modes are identified to explain the crack initiation and propagation mechanisms under dynamic loading. The tensile-shear fracture modes are mainly presented for specimens with different crack inclinations. Differently, the ultimate failure modes change from tensile-shear mode to tensile mode when the rock bridge length is increasing. In addition, numerical results (ANSYS/LS-DYNA) are in good agreement with the experimental results as a whole, which can verify and explain the experimental results. This study is expected to provide guidance for controlling fractured rock masses.

The Hot Ductility of TWIP and TRIP Steels—An Alternative Interpretation

There is significant evidence from light metals that turbulence in casting leads to bifilm defects; enfolded, doubled-over oxide films which act like cracks in the liquid, and are inherited as cracks by the solid. This population of introduced cracks is now known to significantly influence the tensile failure behaviour of light alloys. There is evidence that analogous defects exist in steels. This paper examines the possibility that bifilms may control the hot ductility of TWIP and TRIP steels, and therefore the problems of straightening during continuous casting. Techniques for overcoming these problems are indicated.

Tensile failure behavior of unbonded flexible riser with damaged tensile armor wires

Unbonded flexible risers (UFRs) connect surface production platforms to subsea production systems, and are therefore vital for tasks such as the transportation of oil and gas and the injection of water. The tensile armor layer is the main load layer of UFRs. Once this layer is partially broken, the safety of offshore oil and gas gathering and transportation is seriously threatened. In this study, an 8-layer UFR model is developed to calculate the effects of damaged inner and outer armor wires and boundary conditions on the tensile stiffness, ultimate load capacity, and stress distribution and load ratio of the inner and outer tensile armor layers. Broken inner tensile armor wires are found to have a greater impact on the tensile properties and produce the same torsional buckling failure mode as observed in the field. The influence of the pressure load on the ultimate load capacity of the UFRs is analyzed, and the results demonstrate that the outermost pressure increases the interlayer action between the tensile armor layers and the adjacent layers, thereby reducing the torsional angle of the UFRs under the ultimate tension. Additionally, the innermost pressure is found to have a negligible effect on the ultimate load.

Temperature- and strain-rate-dependent tensile failure behavior of short-fiber-reinforced PEEK composites

This work presents an experimental investigation of the tensile failure behaviors of polyetheretherketone (PEEK), short carbon, and glass-fiber-reinforced PEEK composites at -30–100 °C and various strain rates (10−3–103 s−1). Quasi-static and dynamic tensile tests are conducted, and fracture morphology is characterized by performing scanning electron microscopy to reveal the mechanical properties and failure mechanisms of PEEK and its composites at different temperatures and strain rates. The results indicate that the tensile strength is highly sensitive to temperature and strain rate. At −30 °C and 100 °C, the strain rate sensitivity of the failure strain of the two composites is significantly reduced. In addition, compared with that at 25 °C, the energy absorptivity of PEEK composites decreases at high or low temperatures. Moreover, the primary failure mechanisms of the PEEK composites are interfacial debonding and fiber pull-out at high temperatures and fiber fracture at low temperatures.

2D mesoscale modeling of compressive fracture in concrete using a mesh fragmentation technique

The computational prediction of the failure processes of concrete under compression is still a challenge. Several researchers have proposed mesoscale models to have a better understanding of the influence of the distinct phases of the concrete on the fracture process. In this sense, this work proposes an extension of the mesoscale model proposed by Rodrigues et al. (2016) to describe the complex failure behavior of concrete under compression. In the proposed 2D approach, two layers of interface elements are inserted into the standard finite element mesh to define the potential crack paths using the mesh fragmentation technique. Each layer is formed by a pair of high aspect ratio elements and is responsible for modeling the tensile or frictional shear failure behavior. According to this approach, the compressive failure is a consequence of the combination between tensile and shear failure modes in the mesoscopic scale. The use of these two damage models allows to represent the debonding (opening) between the aggregates and matrix due to local tensile stress concentration, i.e. the fracture propagation in mode-I, as well as the sliding process corresponding to the fracture propagation in mode-II. Furthermore, adopting adequate parameters, these models allow representing the friction condition between the concrete specimen and the steel loading plates. The failure behavior of compression tests with different specimen slenderness as well as the different friction restraints between loading platen and concrete specimen is predicted. The numerical results are compared qualitatively and quantitatively against the experimental results found in the literature, demonstrating that the proposed approach is able to describe the failure process of concrete in compression.

Parametric Influences of Geometric Dimensions on High Temperature Mechanical Behaviors and Damage Mechanisms of Ceramic Matrix Composite and Superalloy Double Bolted Joints

Given multiple material performance advantages, ceramic matrix composite (CMC) material has become one of the most promising hot structural materials used for thermal protection system in hypersonic vehicles. Under harsh thermal exposure of vehicles in flight, the design of connection structure would be a critical issue in improving load-carrying efficiency and ensuring service safety of aircraft structures in service environments. However, little attention was paid on mechanical behavior and its factors affecting the mechanical property of CMC joining at elevated temperature. To address this concern, a 3D finite element model coupled with progressive damage analysis is carried out to predict high temperature tensile properties and failure behavior of single-lap, double-bolt CMC/superalloy joints assembled by two serial protruding-head bolts. In the implementation of progressive damage analysis of 2D plain-woven C/SiC composites, a user-defined subroutine UMAT including a nonlinear constitutive model, 3D Alvaro failure criterion and Tan’s material degradation rule were embedded into the general package ABAQUS® through Fortran program interface. A parametric study considering geometries of joints was performed to evaluate their resultant influence on high temperature tensile behavior and the associated damage mechanisms for the CMC/superalloy double-bolt joint. New findings were provided for full exploitation of high performance through geometric design of ceramic matrix composite hot structure for hypersonic aircraft.

Tensile properties and failure behaviour of continuous kevlar fibre reinforced composites fabricated by additive manufacturing process

ABSTRACT Fused deposition modelling (FDM) is one of the most promising Additive Manufacturing (AM) techniques. FDM technique is capable to print continuous fibre reinforced composite (CFRP). Both researchers and the industrial community are becoming interested in this area. In the present work, Kevlar fibre reinforced composite (KFRCP) was fabricated using Fused deposition modelling (FDM) technique. Onyx material is used as matrix material and continuous kevlar fibre as reinforcement. In this present work influence of the following parameters has been investigated: effect of an increase in kevlar fibre reinforcement starting from 0, 2 to 10 layers in a step-wise manner on tensile strength. An effect of change in kevlar fibre direction, as well as configuration (isotropic, concentric pattern) on tensile strength by fixing 10 layers of kevlar reinforcement. A tensile test was conducted on the specimen in compliance with ASTMD3039. Young’s modulus and stress had been calculated based on experimental results. It was observed that the overall strength of KFRCP was twenty times more compared to virgin CFRP (only onyx). Kevlar fibre has the poorest wettability with the matrix. Poor wettability and lack of impregnation between fibre and matrix result in delamination. Furthermore, delamination with an increase in reinforcement in the FDM process is also discussed. The results obtained will aid designers to select appropriate fibre direction and orientation while developing FRCP parts to prevent delamination.

Effect of Clay Minerals on Tensile Failure Characteristics of Shale.

The effects of mass fraction, elastic modulus, and the spatial distribution of clay minerals on the failure behaviors of shale under the Brazilian disc split are investigated in this study based on a developed PFC2D model. The feasibility of this established numerical model is validated by the load–displacement curves and fracture morphology of shale in the laboratory test. The influences of the mass fraction, elastic modulus, and spatial distribution of clay minerals on the tensile strength and failure behaviors of shale are comprehensively analyzed using the developed numerical model. The results show that the clay content has the strongest influence on the tensile strength of shale. The number of matrix cracks is sensitive to the clay distribution, and the complexity of the matrix fracture network in shale shows a positive correlation with the clay content. In addition, the variation of the clay modulus has a linear correlation with the macro elastic modulus of shale.

Revealing the influence of ultrasound/heat treatment on microstructure evolution and tensile failure behavior in 3D-printing of Inconel 718

Ultrasound is a potential method to enhance the mechanical properties during directed energy deposition (DED), however, its intrinsic strengthening mechanism has not been completely uncovered. In this study, the ultrasound-induced strengthening mechanism has been explored from perspectives of microstructure evolution (i.e., grain size and phase composition), and it has been compared with that of the heat treatment after building without ultrasound. The results indicate that the columnar grain (γ) underwent obvious transition and refinement by inducing ultrasound, along with the changes in the morphology and size of Laves phase. Yet the second phase (i.e., γ′ + γ″, Laves phase, and δ) of heat-treated samples was different than that of the samples obtained by ultrasound. Moreover, combined with grains changes and the quantitative analysis of Laves phase, the tensile properties and fracture mechanism were analyzed. The experimental results demonstrate that the tensile properties were improved by both ultrasound and heat treatment. Among them, the average ultimate tensile stress of samples treated with ultrasound increased by 10% compared to the as-built samples along the scanning direction. Consequently, the main strengthening mechanism of samples by ultrasound was found to be grain refinement, while a large number of strengthening phases (γ′ + γ″) precipitated to strengthen the matrix in heat-treated samples. Thus, clarifying strengthening mechanism is crucial for understanding the mechanical properties of as-built samples.

Tensile and flexural failure behaviors of bolted T-joint consisting of T300/BMP316 composite laminates and TC4 alloy

T-joints are increasingly applied as the connection between vane and case in aero-engines. However, their mechanical behavior and damage mechanisms are unclear, restricting a broader range of applications. In this paper, a bolted T-joint was designed, which was composed of a T300/BMP316 laminated case and TC4 vane, followed by tensile and flexural tests to investigate the mechanical behavior. Subsequently, a progressive damage model based on continuum damage mechanics was employed to predict the bearing capacity and damage evolution of the joints. A comparison between simulation results and the tests shows that the maximum error in displacement is 6.6%, and the maximum error in load is 2.9%. The damage modes are similar, which verifies the reliability of the simulations. The results indicate that the structure reaches the tensile capacity when fiber damage extends to the whole width of the case. And the fiber damage mainly occurs on the loading side and dominates the strength of the T-joint under flexural loading. Massive matrix damage and delamination occur in the laminated case under both loading modes, which reduces the stiffness of the T-joints. Moreover, it is observed that plastic deformation extends on the flange of TC4 vane along the fillet under flexural loading, which aggravates the decrease of structural stiffness. This work is to provide references for the engineering design of the connection structure between aero-engine vanes and the case.

Reliability Assessment by Factor of Safety on the Tensile Failure Behaviour on Military Grade Armour Steel Weldment

Reliability Assessment by Factor of Safety on the Tensile Failure Behaviour on Military Grade Armour Steel Weldment

Tensile Property and Failure Behavior of Copper/Aluminum Dissimilar Friction Stir Welding at Elevated Temperatures

Tensile Property and Failure Behavior of Copper/Aluminum Dissimilar Friction Stir Welding at Elevated Temperatures

Improvement of the dynamic failure behavior of concrete subjected to projectile impact using user-defined material model

The RHT model, one of the concrete material models, is embedded in commercial tools, and is mainly used for impact and explosive analysis with high strain rates. The original RHT model showed sufficiently similar results for the penetration depth measured by experiments in the low impact velocity. However, as the impact velocity increases, the original model has limitations in expressing the dynamic response of the concrete because yield surfaces and fracture behavior, depending on the strain rate, were underestimated. Although previous studies were conducted to improve the RHT model, the input parameters constituting the RHT model were either adjusted to approximate the experimental data. In this study, we propose a model that can express the improved dynamic tensile failure behavior by reflecting the strain rate-dependent parameters. Unlike the methods used in previous studies, the modified model was established that formulates important parameters to fit well with the experiment using user-defined functions. Based on experimental observations, we introduced a nonlinear crack softening model that reflects strain rate-dependent tensile strength and fracture energy to realistically express fracture strain and impact resistance against dynamic loads. In addition, we embedded a damage model that represents the irreversible volumetric deformation caused by pore collapse as the confinement pressure increases. For the verification of the proposed model, numerical simulations for the two experimental tests (i.e., penetration of thick concrete targets and perforation of thin concrete slabs) were performed. The proposed model shows good agreement with the experimental results, and in particular, it showed that the penetration depth and residual velocity are well estimated. Thus, we confirmed that it is superior in representing the resistance and fracture behaviors of the concrete target.

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.

Materials Technology for Heterogeneous Polymer Systems : Part II. Investigation of Motional Heterogeneity in Rubber Vulcanizates

For rubber vulcanizates or crosslinked rubbers, inherent characteristics of rubber elasticity are well known to be mainly controlled by the change in conformational entropy under deformation, causing constrained molecular mobility of rubbery network chains. In this part II of special lecture, 1H-pulsed NMR method is applied to observe the motional heterogeneity in the crosslinked rubbers, related to effects of crosslink density and incorporation of reinforcing carbon black fillers on the tensile failure behaviors under various conditions. Furthermore, as for analysis of thermo-oxidative aging behaviors for the crosslinked rubbers, the relationships between the breaking stretch ratio in tensile measurements, λb, and NMR relaxation properties such as spin-spin relaxation time, T 2, and residual dipolar coupling constant , D res, were discussed to predict the failure properties of small pieces sampled from engineering rubber parts, for which tensile tests could not be easily performed.

Progressive failure characteristics of unidirectional FRP with fiber clustering

For practical fiber reinforced plastic (FRP) structures, fibers are randomly packed in matrix, and some degree of clustering is often observed because of imperfect control of manufacturing process. In this work, a new method to generate random fiber distribution including fiber clustering is proposed according to fiber clustering characteristics of typical micro-image of FRP cross section. Irregularity and nearest neighbor fiber characteristics of random fiber distribution with fiber clustering are analyzed. Two-dimensional geometrically non-linear finite element (FE) modeling on representative volume element (RVE) is conducted to investigate transversely progressive tensile and compressive failure behavior of FRP. Extended linear Drucker-Prager model and cohesive zone model are employed to represent matrix deformation and interfacial debonding. Ultimate strength, fracture strain and crack characteristics of FRP with different degree of fiber clustering are derived and compared. It is shown that fiber clustering tends to result in significant decline and uncertainty of fracture strain and ultimate strength. The characteristics of fiber clustering can lead to two crack modes which affects the macro-scale mechanical properties of FRP.