External Tensile Load Research Articles

The Contact Stress Distribution in a Double Tapered Bolt Joint

Abstract The mechanical problem that occurs when a thin elastic layer (e.g., a part of a composite panel) is inserted between two tapered elastic parts and bolted together is studied. The problem considered is of relevance for situations when it is of value to get a rough estimate of the contact pressure in the elastic layer and, by extension, the contact friction. The intermediate elastic layer (i.e., panel) is assumed to behave like a Winkler foundation, and engineering beam theory is assumed to describe the behavior of the tapered outer parts. The coupling between the transverse stresses in the panel and the longitudinal stress due to an applied external tensile load in the plane of the panel is ignored. By using the influence functions for the tapered parts, one obtains an integral equation involving the compression of the panel as the only unknown function. The integral equation is solved numerically by standard procedures. An experiment was also performed in a way that differs slightly from what is covered by the more general theoretical model. This is due to practical reasons connected to the experiment. It was found that the theoretical model gave results in fair agreement with the experimental results.

Mixed-mode fracture in a soft elastomer

We present an experimental study on mixed-mode crack propagation in thin sheet specimens of a soft silicone elastomer. To introduce mixed-mode loading, we adopted the widely applied pure shear fracture testing geometry, but oriented the initial crack at an inclined angle relative to the direction perpendicular to the external tensile loading. Because of the inclined angle, locally the crack tip was subjected to both tensile and shear loading even though the global loading was tensile, thus resulting in a mixed Mode-I and Mode-II condition for the crack. Altering the inclined angle led to different degrees of mode-mixity and hence different crack propagation trajectories. Using a particle tracking method, we were able to measure the nonlinear deformation fields throughout the entire course of crack propagation. Based on the measured deformation fields, we used J-integral to calculate the energy release rate during crack propagation and found that the results were insensitive to the tangent direction of the crack trajectory, suggesting that the fracture toughness was approximately mode independent. Moreover, the tangent direction of the crack trajectory, when plotted in the reference configuration, was observed to be perpendicular to the direction of maximum principal stretch. The experimental results pave the way for establishing quasi-static mixed-mode fracture criteria for soft silicone elastomer, which has not yet been well understood in the literature.

On crack evolution with texturization of bonding layer in thermal barrier coating

The interface morphology of the bonding layer has a considerable effect on the damage and failure of sandwich-structured thermal barrier coatings. This work investigated the comprehensive effects of a grooved texture produced using laser ablation on the local surface strain, interfacial stress and strain, and crack behavior of the bonding layer in a thermal barrier coating system. The distribution and evolution of the local surface strain was obtained using the digital image correlation method. The interfacial stress, and the strain between the ceramic and bonding layers, were determined through a simulation of the plane-strain model, and the morphology and propagation of cracks were observed in thermal barrier coatings under an external tensile load. The results indicated that the local surface strain of the thermal barrier coating increased with the texturization of the bonding layer, whereas the fluctuation decreased. There were two inflection points in the local surface strain–time curves, corresponding to the initiation of surface cracks and that of interfacial transverse cracks. The surface cracks were initiated earlier than those without the texturization of the bonding layer. However, the behavior of the interfacial cracks was more complicated. If the roughness of the texture, defined as Rc, was small, the surface cracks propagated vertically to the interface between the ceramic and bonding layers, and turned into transverse cracks, leading to a separation of the ceramic layer. If Rc was greater than 22 μm, the surface cracks went further down to the interface between the bonding layer and substrate, and propagated horizontally, resulting in the separation of both the ceramic and bonding layers. Meanwhile, interfacial cracking and separation were deferred. A large roughness resulted in good cohesion between the ceramic and bonding layers, and a high stiffness for the coating, which improved the damage resistance and extended the life of the coating.

Uniaxial Strain-Induced Grain Boundary Migration in Titanium

The mechanical response of a bi-crystal model with a 90° grain boundary under external compressive and tensile loading parallel to the boundary plane normal was investigated with molecular dynamics simulations. The grain boundary was found to migrate along two opposite directions upon compressive and tensile straining, with the formation of inter-connected coherent twin boundary and basal/prismatic boundary. The atomic details of such grain boundary migration were unraveled, which indicated the role of interface dislocations. The temperature effect was also discussed.

Theoretical predictions of size-dependent Young's and shear moduli of single-walled carbon nanotubes

In this study, based on the Force-Heat Equivalence Energy Density Principle, the energy density stored in Single-walled carbon nanotubes (SWCNTs) with different diameters is assumed as the same when SWCNTs with different diameters undergo the same elastic strain under a uniaxial external tensile loading, which is composed of strain energy density and the equivalent curvature energy density. Then, theoretical models without the thickness of SWCNTs for characterizing size-dependent Young's and shear moduli of SWCNTs are established considering the effect of curvature energy. To verify the proposed models, the Young's and shear modulus of SWCNTs in different diameters are predicted, and good agreement is obtained with the available theoretical and numerical simulation results. Besides, the predictions by our models are normalized by graphene values and found the same trends as other scholars. This work contributes to providing a new method to estimate the size-dependent elastic moduli of SWCNTs.

Insight Into the Strengthening Mechanism of the Al-Induced Cross-Linked Calcium Aluminosilicate Hydrate Gel: A Molecular Dynamics Study

Understanding and controlling the mechanical properties of calcium aluminosilicate hydrate (C-A-S-H) gel is essential to the performance improvement of cementing materials. This study characterizes the mechanical properties and failure mechanism of cross-linked C-A-S-H that have Al/Si ratios ranging from 0 to 0.20 by employing the reactive molecular dynamics simulation. In these constructed C-A-S-H models, the Al-induced cross-linking effect on the aluminosilicate chains is well reproduced. With the incorporation of aluminate species, layered C-S-H structure gradually transforms into three-dimensional C-A-S-H. The uniaxial tensile tests show that Al-induced cross-links significantly increase the cohesive force and stiffness of C-A-S-H along both y- and z-directions. In the C-A-S-H model with the Al/Si ratio equal to 0.2, in which all the bridging sites are cross-linked, the toughness along y-direction significantly improves the interlayer mechanical properties compared to those within the layers. The deformation mechanism of the C-A-S-H structure is also studied. Results show that the depolymerization of the calcium aluminosilicate skeleton is the main route to uptake the loading energy. Both the increase of y- and z-directional strength of the structure can be related to the increasing polymerization of aluminosilicate chains along that direction. This demonstrates the important role of aluminosilicate chains in resisting the external tensile loading. Besides, during the failure process in C-A-S-H elongation, the hydrolysis reactions of calcium silicate skeleton are caused by the coupling effect of loading and interlayer water “attack.” While the Al-O-Si bond breakage results from the protonation of bridging oxygen atom, the hydrolytic reaction of Si-O-Si is initiated by five-coordinate silicon formation. Both pathways weaken the bridging bond and thus result in the breakage of T-O-Si, where T is Al or Si.

Assessment of Ti-6Al-4V particles as a reinforcement for AZ31 magnesium alloy-based composites to boost ductility incorporated through friction stir processing

Poor ductility is the primary concern of magnesium matrix composites (MMCs) inflicted by non-deformable ceramic particle reinforcements. Metal particles which melt at elevated temperature can be used as reinforcement to improve the deformation characteristics. Ti-6Al-4V particles reinforced AZ31 MMCs were produced through friction stir processing (FSP) which was carried out in a traditional vertical milling machine. The microstructural features as well as the response to external tensile load were explored. A homogenous distribution of Ti-6Al-4V was achieved at every part of the stir zone. There was no chemical decomposition of Ti-6Al-4V. Further, Ti-6Al-4V did not react with Al and Zn present in AZ31 alloy to form new compounds. A continuous strong interface was obtained around Ti-6Al-4V particle with the matrix. Ti-6Al-4V particles underwent breakage during processing due to severe plastic strain. There was a remarkable refinement of grains in the composite caused by dynamic recrystallization in addition to the pinning of smaller size broken particles. Dense dislocations were observed in the matrix because of plastic deformation and the associated strain misfit. Ti-6Al-4V particles improved the tensile behavior and assisted to obtain appreciable deformation before fracture. Brittle mode of failure was avoided.

Investigation of the microstructure and mechanical performance of bimetal components fabricated using CMT-based wire arc additive manufacturing

Traditionally, wear-resistant components are manufactured by cladding hard facing material on the base metal. This production process is typically complicated, expensive, and time-consuming. This study proposes a method of fabricating components with high wear resistance requirements utilizing cold metal transfer based wire and arc additive manufacturing with hard facing welding wire as the consumable material. Thin-walled and block components were manufactured by depositing a combination of a low alloy steel, ER80S-G, and a hard facing material, MF6–55GP. Microstructure characterization and mechanical properties (hardness, tensile and Block-on-Ring wear test) were performed. The results revealed that the ER80S-G/MF6–55GP bimetal components were able to be fused with no detectable defects near the border. As the deposited height was increased, the residual stress also increased; this internal residual stress combined with the external tensile load lead to a very low tensile strength of 447.79 ± 24.32 MPa of the ER80S-G/MF6-55GP/ER80S-G sandwich structure. The microstructures, constituent phases, and hardness distributions differ greatly among the layers due to their different thermal histories. The wear weight loss varies as the load condition changes for both the MF6-55G and Cr12MoV steels. Compared to Cr12MoV, MF6-55GP weld metal exhibits better wear resistance at higher loads in dry sliding wear tests.

Structural Analysis of 2G HTS Tapes under Different Loading Conditions for HTS Power Cable using Finite Element Modeling

In High Temperature Superconducting (HTS) power cable, HTS tapes are wound helically around a circular former and are subjected to different types of mechanical loads during manufacturing, transportation and installation of cable. The strain developed within the HTS tape during these processes may affect the superconducting properties of the tape. In the present work, 3D structural finite element (FE) models using ANSYS® are developed to obtain the strain behaviour of the tape under different loading conditions, considering the layered sandwich composite structure of 2G HTS tapes. The analysis is carried out with axial tensile and twisting loads on the tape, during helical winding of tape around the former and a combined effect of helical winding with external tensile and bending loads. The result obtained from FE simulation due to applied tensile load is compared with the established experimental result, which shows a good agreement. Further, the strain developed within the tape affects the critical current. Therefore, the strain is coupled with an empirical relation to obtain the critical current degradation of the tape. The FE analysis is carried out for five different winding pitches and four different bending radii with YBCO layer in the downward position and the corresponding critical currents are estimated. Further, a minimum winding pitch is obtained, below which the rapid degradation of critical current is initiated. The results show that the HTS tape with YBCO in downward position can withstand more amount of external load without affecting the critical axial strain of the tape.

The Importance of Geometrical Parameters on the Mechanical Stability of Roebel Cables

AC loss from Roebel cables with high-temperature superconducting strands are comparatively less, and they possess large current carrying capacity since they have a transposed structure. However, the strands should be strong enough to withstand various types of external loads during their operation. The present work simulates the performance of the Roebel strand against an external tensile load using 3-D finite element analysis, and the importance of geometrical parameters on the mechanical stability of Roebel cables is investigated. Results were then compared with another work where the analyses were performed on a monolithic Roebel strand. We concluded that the typical twisting of the strands is an important parameter that cannot be ignored when optimizing a Roebel cable. Hence, the stress induced in a Roebel strand against an external load depends not only on the geometrical parameters but also on the typical twisting of the strand.

Failure Analysis of Unidirectional Ceramic Matrix Composite Lamina and Cross-Ply Laminate under Fiber Direction Uniaxial Tensile Load: Cohesive Zone Modeling and Brittle Fracture Mechanics Approach

The current research work presents the computational micromechanical analysis of the room temperature tensile failure behavior of unidirectional (UD) and cross-ply (0/90) ceramic matrix composites (CMCs). For computational micromechanical analysis, three-dimensional (3D) representative volume element (RVE) and multi-fiber multilayer RVE (M2 RVE) models are generated that are representative of the lamina and the laminate under investigation. The RVE and M2 RVE models are generated by replicating the fiber distribution, and the placement of the fibers observed in a microscopic image of an actual CMC laminate. The generated RVE models consist of the discrete representation of individual constituent phases of the CMC such as fibers, interphase, matrix, and the fiber–interphase interface region. Under the applied external tensile load, the fiber–interphase interface interactions are modeled using the cohesive elements that follow the bilinear traction separation law. The matrix, fiber, and interphase materials failure behavior is captured using a brittle cracking model. In order to validate the proposed numerical methodology, the predicted average stress–strain curve at the UD laminate level is compared to the experimental stress–strain curve reported in the literature. In addition, the observed different phases in the predicted stress–strain curve are validated with the literature data. Using the proposed numerical methodology, a detailed local stress–strain and damage analysis leads to an observation that the so-called ductile stress–strain behavior (kink in the stress–strain curve) of a CMC UD laminate under uniaxial fiber direction tensile loads is mainly caused by the matrix damage initiation. Apart from the SiC material properties such as strength and fracture energy, it is also observed that the RVE size influences the average strength and failure strain predictions using computational micromechanics.

A phenomenological constitutive model for semicrystalline two-way shape memory polymers

Recently, two-way shape memory effect (2W-SME) has been demonstrated in several types of shape memory polymers (SMPs). Unlike classical one-way shape memory effect (1W-SME), these polymers can switch back and forth repeatedly between two different shapes without subsequent programming procedure. The reversible actuation can be realized either under a constant external tensile load, which is referred to as quasi 2W-SME, or under zero load, which is referred to as true 2W-SME. Most recently, actuation under an external compressive load, which is referred to as advanced 2W-SME, has also been discovered. Test results have shown that semicrystalline 2W-SMPs exhibit 2W-SME in two distinct regions due to two different mechanisms: one is due to entropic elasticity above the crystallization temperature, and the other is due to melt/crystallization transition below the crystallization temperature. While several constitutive models have been developed over the years for semicrystalline 2W-SMPs, there is currently a lack of effort towards modeling the true and advanced 2W-SME within the two-mechanism framework. In this study, we developed a thermomechanical constitutive model which captured both the entropic elasticity and melt/crystallization events. The modeling results and test results show reasonable agreement. It is found that the model captured the three types of 2W-SMEs: quasi 2W-SME, true 2W-SME, and advanced 2W-SME. It is also found that proper tensile programming before the first thermomechanical cycle can make a semicrystalline SMP exhibit all the three types of 2W-SMEs. This study may serve as a design tool to enhance applications of semicrystalline 2W-SMPs in engineering structures and devices.

A viscoplastic model for void growth under dynamic loading conditions

We present a dynamic theoretical viscoplastic model of voids subjected to external dynamic tensile loadings. The material viscosity and temperature are factors that are considered in the dynamic evolution of voids in viscoplastic materials. We focus on the thermal effect; the temperature affects the thermal softening of the material strength and also the material viscosity. Viscous flow is the dominant growth mechanism under high stresses and rates based on the results of the calculations for dynamic void growth predictions. The factors are independently studied, and the correlations are systematically analyzed.

Contribution of nascent cohesive fiber-fiber interactions to the non-linear elasticity of fibrin networks under tensile load

Fibrin is a viscoelastic proteinaceous polymer that determines the deformability and integrity of blood clots and fibrin-based biomaterials in response to biomechanical forces. Here, a previously unnoticed structural mechanism of fibrin clots' mechanical response to external tensile loads is tested using high-resolution confocal microscopy and recently developed three-dimensional computational model. This mechanism, underlying local strain-stiffening of individual fibers as well as global stiffening of the entire network, is based on previously neglected nascent cohesive pairwise interactions between individual fibers (crisscrossing) in fibrin networks formed under tensile load. Existence of fiber-fiber crisscrossings of reoriented fibers was confirmed using 3D imaging of experimentally obtained stretched fibrin clots. The computational model enabled us to study structural details and quantify mechanical effects of the fiber-fiber cohesive crisscrossing during stretching of fibrin gels at various spatial scales. The contribution of the fiber-fiber cohesive contacts to the elasticity of stretched fibrin networks was characterized by changes in individual fiber stiffness, the length, width, and alignment of fibers, as well as connectivity and density of the entire network. The results show that the nascent cohesive crisscrossing of fibers in stretched fibrin networks comprise an underappreciated important structural mechanism underlying the mechanical response of fibrin to (patho)physiological stresses that determine the course and outcomes of thrombotic and hemostatic disorders, such as heart attack and ischemic stroke. Statement of SignificanceFibrin is a viscoelastic proteinaceous polymer that determines the deformability and integrity of blood clots and fibrin-based biomaterials in response to biomechanical forces. In this paper, a novel structural mechanism of fibrin clots’ mechanical response to external tensile loads is tested using high-resolution confocal microscopy and newly developed computational model. This mechanism, underlying local strain-stiffening of individual fibers as well as global stiffening of the entire network, is based on previously neglected nascent cohesive pairwise interactions between individual fibers (crisscrossing) in fibrin networks formed under tensile load. Cohesive crisscrossing is an important structural mechanism that influences the mechanical response of blood clots and which can determine the outcomes of blood coagulation disorders, such as heart attacks and strokes.

FEM Analyses of Mechanical Behavior and Design Method for Bolted Joints Consisting of Dissimilar T-shape Flanges Subjected to External Tensile Loads

FEM Analyses of Mechanical Behavior and Design Method for Bolted Joints Consisting of Dissimilar T-shape Flanges Subjected to External Tensile Loads

Are Homeostatic States Stable? Dynamical Stability in Morphoelasticity

Biological growth is often driven by mechanical cues, such as changes in external pressure or tensile loading. Moreover, it is well known that many living tissues actively maintain a preferred level of mechanical internal stress, called the mechanical homeostasis. The tissue-level feedback mechanism by which changes in the local mechanical stresses affect growth is called a growth law within the theory of morphoelasticity, a theory for understanding the coupling between mechanics and geometry in growing and evolving biological materials. This coupling between growth and mechanics occurs naturally in macroscopic tubular structures, which are common in biology (e.g., arteries, plant stems, airways). We study a continuous tubular system with spatially heterogeneous residual stress via a novel discretization approach which allows us to obtain precise results about the stability of equilibrium states of the homeostasis-driven growing dynamical system. This method allows us to show explicitly that the stability of the homeostatic state depends nontrivially on the anisotropy of the growth response. The key role of anisotropy may provide a foundation for experimental testing of homeostasis-driven growth laws.

Transformation induced plasticity effect under tensile and compression stresses in nanostructured bainite

TRIP effect and mechanical stability of retained austenite are important factors which must be considered when talking about the ductility in nanostructured bainite. Meanwhile, different parameters affect austenite mechanical stability among those the deformation mode is of considerable importance. This article aims to compare the capability of high carbon retained austenite to transform to martensite when being subjected to external tensile and compressive mechanical loads in those materials. Scanning electron microscopy were used to investigate the microstructural features and interrupted tensile and compression tests were implemented to evaluate austenite stability. X-ray analyses were carried out to evaluate the austenite to martensite evolution during straining the samples and three different mathematical approaches were also implemented to express the austenite mechanical stability by mathematical constants. Results indicated that higher yield strength, enhanced true plastic strength and higher ductility could be obtained in compression deformation state. Moreover, tensile tests strongly simulated the martensite formation while compressive deformation mode opposed the volume expansion associated with austenite to martensite transformation. Accordingly, austenite was mechanically more stable during compression and it transformed to martensite more gradually comparing to that of tension.

Through-thickness welding residual stress and its effect on stress intensity factors for semi-elliptical surface cracks in a butt-welded steel plate

The through-thickness distribution of welding residual stress (RS) in a 30-mm-thick butt-welded Q345qD steel plate is investigated through experimental measurements and finite-element simulations. The simulated RS fields agree reasonably with the measured results for both surface and internal stresses. In addition, the weight function and finite-element methods are used to investigate the stress intensity factors (SIFs) at the surface and deepest points of semi-elliptical surface cracks subjected to a combination of external tensile load and through-thickness welding RS. Different crack aspect ratios and relative depths are analyzed. The results reveal that the longitudinal RS is always tensile through the plate thickness, making the SIFs of the surface and deepest points larger than those without considering the longitudinal RS. However, the transverse RS through the thickness presents tension–compression–tension, with the tensile transverse RS causing the SIFs to increase. When the crack tip enters the compressive stress region, the compressive stress offsets the external load and causes the SIFs to decrease.

3D auxetic single material periodic structure with ultra-wide tunable bandgap

The design and the combination of innovative metamaterials are attracting increasing interest in the scientific community because of their unique properties that go beyond the ones of natural materials. In particular, auxetic materials and phononic crystals are widely studied for their negative Poisson’s ratio and their bandgap opening properties, respectively. In this work, auxeticity and phononic crystals bandgap properties are properly combined to obtain a single phase periodic structure with a tridimensional wide tunable bandgap. When an external tensile load is applied to the structure, the auxetic unit cells change their configurations by exploiting the negative Poisson’s ratio and this results in the tuning, either hardening or softening, of the frequencies of the modes limiting the 3D bandgap. Moreover, the expansion of the unit cell in all the directions, due to the auxeticity property, guarantees a fully 3D bandgap tunability of the proposed structure. Numerical simulations and analytical models are proposed to prove the claimed properties. The first experimental evidence of the tunability of a wide 3D bandgap is then shown thanks to the fabrication of a prototype by means of additive manufacturing.

Nanomechanics of actin filament: A molecular dynamics simulation.

Actin is known as the most abundant essentially protein in eukaryotic cells. Actin plays a crucial role in many cellular processes involving mechanical forces such as cell motility, adhesion, muscle contraction, and intracellular transport. However, little is known about the mechanical properties of this protein when subjected to mechanical forces in cellular processes. In this article, a series of large-scale molecular dynamics simulations are carried out to elucidate nanomechanical behavior such as elastic and viscoelastic properties of a single actin filament. Here, we used two individual methods namely, all-atoms and coarse-grained molecular dynamics, to evaluate elastic properties of a single actin filament. In the other word, based on Brownian motions of the filament and using the principle of the equipartition theorem, in aqueous solution, tensile stiffness, torsional rigidity, and bending rigidity of the single actin filament are studied. The results revealed that increasing the sampling window time leads to convergence of obtained mechanical properties to the experimental values. Moreover, in order to investigate viscoelastic properties of a single actin filament, constant force steered molecular dynamics method is used to apply different external tensile loads and perform five individual creep tests on the molecule. The strain-time response of the filament for each creep test is obtained. Based on the Kelvin-Voigt model, the results reveal that a single actin filament shows a nonlinear viscoelastic behavior, with a Young's modulus of 2.85 GPa, a viscosity of 4.06 GPa.ns, and a relaxation time in the range of 1.42 ns which were measured here for the first time at the single filament level. The findings of this article suggest that molecular dynamics simulations could also be a useful tool for investigating the mechanical behavior of bio-nanomaterials.