Variations In Mechanical Behavior Research Articles

Tensile behavior of diffusion bonded AA6061 - AA6061 with variation in cooling method

Hot isostatically pressed AA6061 cladding is an important structural component of the high performance, Zr-laminated U-10Mo monolithic fuel system for the application in research and test reactors. In this study, the mechanical behavior of two diffusion bonded aluminum alloy, AA6061, was examined using tensile testing. Solid-to-solid diffusion bonding between two pieces of AA6061 was performed by isothermal annealing at 560 °C for 1.5 h, and diffusion couples were subsequently cooled via three different cooling methods: furnace cooling, air cooling, and water quenching. Dog-bone shaped tensile specimens, with 10 mm in gauge length (with diffusion bonded interface in the middle), and 1.5 × 1.5 mm2 gauge cross-sections, were fabricated from the diffusion bonded AA6061 by electro-discharge machining. Yield strength (% EL at failure) of furnace cooled, air cooled and water quenched tensile specimens determined was 82–89 MPa (10–30%), 112–116 MPa (10–14%), and 149–164 MPa (10–17%), respectively. This variation in mechanical behavior was examined with cooling-rate dependent, concentrated precipitation of Mg2Si at the diffusion bonded interface, with due respect for mechanical properties of the AA6061 alloy that inherently vary as a function of cooling rate from 560 °C. Finite element analysis using ABAQUS was employed to augment experimental findings with the appropriate microstructural constituents and alloy properties. Results suggest that the strength is dominated by matrix/bulk properties of AA6061, while ductility is strongly influenced by the cooling method dependent presence of Mg2Si precipitates at the interface.

Effect of microsegregation and heat treatment on localised γ and γ’ compositions in single crystal Ni-based superalloys

The present work investigates the impact of residual segregation on the underlying microstructure of a 3rd generation single crystal, nickel-based superalloy to understand potential variation in mechanical behaviour between dendrite cores and interdendritic regions. Despite the applied heat-treatments, chemical variation between dendrite cores and interdendritic regions persisted particularly for elements Re, Nb and Ta. Atom probe tomography (APT) was utilized for its nanoscale capability to map site-specific chemical changes in the γ matrix, γ’ precipitates and across the γ/γ’ interface. Greater interfacial segregation of Re, matched by a corresponding depletion of Ni were observed within dendrite cores, with the extent found to increase following heat treatment. Differences in lattice parameters between dendrite cores and interdendritic regions were identified, with larger lattice misfits associated with interdendritic regions.

Classification of progressive failure and mechanical behavior of dissimilar material hybrid joints at varying temperatures

This research illustrates the progressive failure mechanisms and variation in the mechanical behavior of dissimilar materials hybrid joints at elevated temperatures. For this purpose, a novel in-situ data fusion scheme was developed from experimental analysis which was validated through a coupled computational approach. The hybrid joint consisted of CFRP/Al worksheets joined through a steel bolt. The experimental analysis revealed distinct failure mechanisms in worksheets, i.e., yielding in Al sheet and a mixed failure mode in CFRP sheet while no signs of failure were observed in the steel bolt. Further, the progressive damage in the CFRP sheet was classified as a three-staged process which comprised elastic strain phase, crack initiation and progressive damage phase, and unstable fracture phase by correlating the temperature (Infrared Thermography) and strain variations (Digital Image Correlation). Further, degradation in mechanical behavior from room temperature was evaluated at three elevated temperatures, i.e., 50 °C, 75 °C, and 100 °C. A significant drop in mechanical properties (maximum strength and nominal stiffness) was noticed at high temperatures while a transition in failure mode was also evident (ply bending and pronounced fiber breakage) in comparison to the joints tested at room temperature. In computational analysis, Tsai–Wu, Maximum Stress, and Puck’s static failure criteria were coupled with the element deletion model to ascertain the critical ply and progressive damage in the joint. The experimental results were found in good agreement with the computational results in terms of critical ply and load-carrying behavior. In summary, this research helps to understand the progressive failure and variation in mechanical behavior about high temperatures in hybrid joints which can be extended to other dissimilar materials configurations as well.

Effect of constituent content on mechanical behaviors of ultra-high performance seawater sea-sand concrete

• The variation of mechanical behavior with sea shell contents was investigated. • The preferable content of coarse aggregate for UHP-SSC matrix was 10% by volume. • The utilization of basalt FRP minibars can enhance strength and toughness of UHP-SSC. In this study, the mechanical behaviors of ultra-high performance seawater sea-sand concrete were investigated considering various constituent contents of sea shell (SH), coarse aggregate (CA), and basalt fiber reinforced polymer minibars (MB). Experimental results reveal that the mechanical strength first increased and then decreased as the SH content increased, which was attributed to the evolution of macroscopic pores. CA, which preferable content was 10%, hurt the workability and flexural strength of the matrix; in contrast, owing to its skeletal effect, the compressive strength increased at a small content of CA. Moreover, the utilization of the MB increased the compressive strength and flexural toughness and this enhancement is positively correlated with the increase in the minibar content.

Ni solute segregation and associated plastic deformation mechanisms into random FCC Ag, BCC Nb and HCP Zr polycrystals

Different types of grain-boundary (GB) solute segregation in nanocrystalline alloys have been described in the literature as being either homogeneous or heterogeneous, which differently impacts their mechanical properties. In heterogeneous segregation, solute atoms tend to cluster along certain GB areas, while other GB regions remain solute-free. This phenomenon is evidenced with the segregation of Ni solute in nanocrystalline FCC Ag. Yet the physical origin for this segregation behavior and its existence in non-FCC alloys are not fully determined. Here, hybrid Monte-Carlo and molecular dynamics simulations were used to study the segregation of Ni solutes (4 at.%) into nanocrystalline FCC Ag, BCC Nb and HCP Zr metals at their solubility limit temperature and the same homologous temperature (0.405·Tm), respectively. A range of segregation configurations was found: Fully heterogeneous segregation in Ag96Ni4 at 500 K, homogeneous segregation with second-phase precipitates in Nb96Ni4 at 1110 K, homogeneous segregation with dispersion of small-scale Ni clusters in Nb96Ni4 at 1564 K and Zr96Ni4 at 464 K, and fully homogeneous segregation with amorphous intergranular films in Zr96Ni4 at 1118 K. We rationalize these changes by quantifying the Ni solute interactions at GBs. Furthermore, significant variations in mechanical behavior and associated plastic deformation mechanisms are shown for each alloy due to their different segregation behaviors. It is found that strain-localized shear banding is the most significant at interfaces with homogeneous solute segregation containing second-phase precipitates and absent with segregation leading to amorphous intergranular films. These findings underscore the importance of solute interactions in profoundly altering segregation and mechanical behavior in stable nanocrystalline alloys.

Investigation on the use of reclaimed asphalt pavement along with steel fibers in concrete

Poor disposal and handling of asphalt material in construction activities has a great effect on the environment. Despite the use of asphalt material in other activities, a high percentage of it is poorly handled in Uganda. For this, the present study aimed to investigate the mechanical performance of reclaimed asphalt pavement (RAP) along with steel fibers in concrete and the variation of mechanical behavior concerning different curing times with the optimal RAP aggregate-substitute ratio. The result showed that the mechanical and physical properties of the fine and coarse aggregates used suited the replacement when compared with BS EN standard. Workability of fresh concrete is reduced as the percentage RAP increases in the mixture. This reduction was caused due to the asphalt mortar coating on the RAP aggregates, dirt particles and the irregular shape of aggregates. The compressive strength increases and decreases afterward with the increase of the percentage RAP replacement ratio. This occurred due to the presence of oils in the bitumen and weak bond between the asphalt binder coating around the RAP aggregates. When the steel fibers increase, the split strength increases along with curing time. A maximum savings of 6.13% of RAP was accomplished by incorporating 60% RAP replacement mix. For the Uganda scenario, this work serves as a guide for excess RAP application in construction activities. Using reclaimed asphalt materials provides a long-term solution for reducing the cost of materials and end-of-life materials disposal in the landfill.

Combining Unique Planar Biaxial Testing with Full-Field Thickness and Displacement Measurement for Spatial Characterization of Soft Tissues.

Soft tissues rely on the incredible complexity of their microstructure for proper function. Local variations in material properties arise as tissues develop and adapt, often in response to changes in loading. A barrier to investigating the heterogeneous nature of soft tissues is the difficulty of developing experimental protocols and analysis tools that can accurately capture spatial variations in mechanical behavior. In this article, we detail protocols enabling mechanical characterizations of anisotropic, heterogeneous soft tissues or tissue analogs. We present a series of mechanical tests designed to maximize inhomogeneous strain fields and in-plane shear forces. A customized, 3D-printable gripping system reduces tissue handling and enhances shear. High-resolution imaging and laser micrometry capture full-field displacement and thickness, respectively. As the equipment necessary to conduct these protocols is commercially available, the experimental methods presented offer an accessible route toward addressing heterogeneity. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Unique biaxial testing of soft tissues and tissue analogs Basic Protocol 2: Full-field thickness measurement of soft tissues and tissue analogs Support Protocol 1: Creating and speckling cruciform-shaped samples for mechanical testing Support Protocol 2: Creating custom gripping system to minimize sample handling.

Radial variations in mechanical behaviour and fibrillar structure in annulus fibrosus has foundations at molecular length-scale: Insights from molecular dynamics simulations of type I and type II collagen molecules

Radial variations in mechanical behaviour and fibrillar structure in annulus fibrosus has foundations at molecular length-scale: Insights from molecular dynamics simulations of type I and type II collagen molecules

Microstructural evolution and mechanical behavior of Mg/Al laminated composite sheet by novel corrugated rolling and flat rolling

AZ31B Mg/5052 Al laminated composite sheet with superior mechanical property and good sheet shape was fabricated by novel corrugated roll/flat roll corrugating rolling and flat roll/flat roll flat rolling (CFR) at elevated temperatures. The microstructural evolution and mechanical behavior variation of the composite sheet under CFR hot rolling condition were investigated by experimental and numerical simulation methods. The results show that first-pass corrugated rolling induces relatively high and inhomogeneous shear strain in the Mg side and various corrugated interface positions at a low reduction of 35%. It leads to significant grain refinement, outstanding basal texture modification as well as tensile twin activation Mg alloy, which perfectly coordinates the plastic deformation between hard-to-deform Mg and ductile Al and achieve the strong interface metallurgy bonding in Mg/Al sheet and also significantly improves the mechanical properties of Mg/Al composite sheet. The annealing before second-pass flat rolling causes the pronounced static recrystallization and grain growth of Mg alloy in corrugated-rolling Mg/Al sheet, and the formation of ~25 μm thick interfacial compound layer consisted of Mg17Al12 and Al3Mg2 two sublayers. Second-pass flat rolling with a reduction of 30% further imposes severe inhomogeneous shear deformation on the composite sheet, which results in the formation of a wave-shape three-dimensional bonding interface, and the interface compound layers cracking at peak and waist interface positions or fragmenting into well-aligned discrete particles to the bonding interface, in addition to substantial matrix microstructure refinement, texture modification and twin activation in Mg alloy. Such interface structure greatly enhances the interface bonding force of the Mg/Al composite sheet by the larger interface contact area, mechanical gearing effect as well as particle pinning effect. Hence the significant microstructural refinement, strong interface bonding and low residual stress induced by CFR process account for the excellent performance of the Mg/Al laminated composite sheet.

Computational Investigation of the Effect of Network Architecture on Mechanical Properties of Dynamically Cross‐Linked Polymer Materials

AbstractDynamically cross‐linked polymer networks have attracted significant interest in recent years due to their unique and improved properties including increased toughness, malleability, shape memory, and self‐healing. Here, a computational study on the mechanical behavior of dynamically cross‐linked polymer networks is presented. Coarse grained models for different polymer network configurations are established and their mechanical properties using molecular dynamics (MD) simulations are predicted. Consistent with the experimental measurements, the simulation results show that interpenetrating networks (IPN) withstand considerably higher stress compared to the single networks (SN). Additionally, the MD results demonstrate that the origin of this variation in mechanical behavior of IPN and SN configurations goes back to the difference in spatial degrees of freedom of the noncovalent cross‐linkers, represented by nonbonded interactions within the two system types. The results of this work provide new insight for future studies on the design of systems with dual dynamic cross‐linkers where one linkage exchanges rapidly and provides autonomic dynamic character, while the other is a stimulus responsive dynamic covalent linkage that provides stability with dynamic exchange on‐demand.

Interactions of negative strain rate sensitivity, martensite transformation, and dynamic strain aging in 3rd generation advanced high-strength steels

Medium Mn transformation-induced plasticity (TRIP) steels, a subgroup of third generation advanced high-strength steels (AHSS), often present a combination of both dynamic strain aging (DSA) and TRIP. It has been previously shown that TRIP coincides with the passage of strain bands due to DSA, but their interdependence has not been well-established. This study seeks to explore the interactions between the two phenomena as well as the commonly-observed negative strain rate sensitivity. Digital image correlation (DIC) and in-situ magnetic measurements of the retained austenite fraction were employed to demonstrate the variations in mechanical behavior with increasing strain rate. Strain rate jump tests provided measurements of the strain rate sensitivity and were combined with either DIC to characterize PLC bands or with magnetic measurements to measure variations in the martensite fraction during the jumps. Finally, the micromechanics defining the peculiar bursts of martensite transformation in response to strain rate jumps are discussed in terms of a competition between dislocation mobility and austenite stability.

Estimation of mechanical strength for pre-strained 316L austenitic stainless steel by small punch test

During pre-strain process of 316L austenitic stainless steel, the increase in dislocation density and the appearance of mechanical twinning lead to the variation of mechanical behavior with pre-strain. In this study, the effect of pre-strain on strength parameter and deformation energy was discovered by small punch test. The results show that yield strength and saturated elastic energy increase with the increase in pre-strain. But fracture energy decreases with the increase in pre-strain, and maximum load remains invariable. Load method and energy method were compared to estimate mechanical strength of pre-strained material. It is found that, energy method without artificial factor and with physical meaning is more suitable to estimate yield strength than load method, while load method is more suitable to estimate ultimate tensile strength than energy method. Moreover, the effects of pre-strain and temperature were coupled in the energy method to estimate yield strength of pre-strained specimens at different temperatures.

Mechanical Properties of Nanocrystalline and Amorphous Gallium Oxide Thin Films

Nanocrystalline and amorphous Ga2O3 films (≈200 nm) with variable structural quality are produced by sputter‐deposition by varying the substrate temperature (Ts = 25–700 °C). The effect of Ts is significant on the microstructure and mechanical behavior of Ga2O3 films. The variation in mechanical behavior studied by nano‐indentation and nano‐scratch testing reveal distinct trends, which are directly related to the structure and morphology of Ga2O3 films. All the Ga2O3 films deposited at Ts < 500 °C are amorphous; the amorphous‐to‐crystalline transformation occurs at Ts = 500 °C. Ga2O3 films deposited at Ts ≥ 500 °C are nanocrystalline, β‐phase. The corresponding mechanical characteristics, namely the hardness (H) and elastic modulus (Er), show a strong correlation with structural characteristics. The H and Er increases from 17 to 27 GPa and 250 to 290 GPa, respectively, with increasing Ts from 25 to 700 °C. The plasticity index, which is the ratio of H/Er, is almost constant for the Ga2O3 films. The strain‐rate sensitivity measurements performed to determine the applicability in practical applications indicate the best performance of size controlled, nanocrystalline Ga2O3 films, which can be mechanically regarded as nano‐composite structures. The mechanical characteristics, scratch behavior, and strain rate sensitivity indicate the role of microstructure on the mechanical performance of Ga2O3 films.

ANALISA EKSPERIMENTAL MODULUS ELASTISITAS BAHAN KOMPOSIT GLASS FIBER REINFORCED PLASTIC (GFRP) BERDASARKAN VARIASI DIAMETER SERAT AKIBAT BEBAN IMPAK LAJU REGANGAN TINGGI

<span class="longtext"><em><span>GFRP composite is one of the alternative materials that the most common as a replacement for metal. This material has a light weight, easy to shape, good strength, and the production cost is relatively cheaper. This study aims to investigate the effects of fiber diameter variation of mechanical behavior, particularly on the load of high strain rate impact. The application of impulse momentum theory in the elastic region is the basic science for this case. The AGC apparatus is equipment that used for this test because it could generate the high strain wave rate in the single direction loading. Specimen is placed in the position of tight end against the end of the input bar. The results showed that the increase in fiber diameter variations affect the value of E that is produced. Thus, it is become a recommendation for the use of this material in certain circumstances.</span></em></span>

Variation over time of excavated soil properties treated with surfactants

Foaming agents are frequently used to dig tunnels in soft ground. These additives are often considered to be biodegradable. However, the soil fine material of excavated treated soils is generally classified as waste, stored, and not used again. The foaming agent addition affects the hydromechanical property of the soil, and the resulting evolution of the soil remains poorly understood. This study evaluated the impact of surfactants on the potential of reuse of excavated soil. For this purpose, the degradation mechanisms of the treatment were first analyzed and quantified. Standard geotechnical tests were then used to characterize the evolution of hydromechanical properties of the treated soil. The foam state of surfactant was the driving force of the observed physical property changes. The half-life of this altered state was quite short on the order of days, and the material recovered its initial mechanical properties. On the other hand, the presence of surfactant in liquid form affected the hydraulic and viscous properties over longer time periods. Concerning the mechanical behavior variation, the compressibility index of the argillaceous soil passed from 0.12 to 0.24 after treatment; the friction angle of treated soil decreased to 19° and recovered the initial value of 23° after 20 days. The viscosity of more sandy soil was reduced by approximately 100-fold after treatment. This viscosity was recovered much longer after the mechanical one after about 2 months. The hydraulic permeability decreased with the introduction of the foam from 3.4 × 10−9 to 9.6 × 10−10 m/s. After 1 month, the total recovery had not yet occurred. The statistical analysis using PCA on mechanical, hydraulic, and rheological parameters measured as a function of time after the addition of the surfactant demonstrated that the surfactant was degraded over time and the initial conditions were approached.

Biaxial experimental and analytical characterization of a dielectric elastomer

Electroactive polymers (EAPs) have emerged as a strong contender for use in low-cost efficient actuators in multiple applications especially related to biomimetic and mobile-assistive devices. Dielectric elastomers (DE), a subcategory of these smart materials, have been of particular interest due to their large achievable deformation and favourable mechanical and electro-mechanical properties. Previous work has been completed to understand the behaviour of these materials; however, their properties require further investigation to properly integrate them into real-world applications. In this study, a biaxial tensile experimental evaluation of 3M™ VHB 4905 and VHB 4910 is presented with the purpose of illustrating the elastomers’ transversely isotropic mechanical behaviours. These tests were applied to both tapes for equibiaxial stretch rates ranging between 0.025 and 0.300 s−1. Subsequently, a dynamic planar biaxial visco-hyperelastic constitutive relationship was derived from a Kelvin–Voigt rheological model and the general Hooke’s law for transversely isotropic materials. The model was then fitted to the experimental data to obtain three general material parameters for either tapes. The model’s ability to predict tensile stress response and internal energy dissipation, with respect to experimental data, is evaluated with good agreement. The model’s ability to predict variations in mechanical behaviour due to changes in kinematic variables is then illustrated for different conditions.

Understanding the mechanism for the mechanical property degradation of a lithium disilicate glass-ceramic by annealing.

Post-crystallization annealing above the Tg was applied to a lithium disilicate glass-ceramic with microstructure consisting of glassy matrix and rod-like lithium disilicate crystals, effect of the annealing on the mechanical behavior was investigated. Flexural strength and VIF toughness of the glass-ceramic unexpectedly decreased after the annealing. The mechanical behavior variation was understood based on residual micro-stress analysis. Coefficient of thermal expansion for the glassy matrix presented a tendency to increase after the annealing, which would enlarge the thermal expansion mismatch between the glassy matrix and the lithium disilicate crystals. As a result, the residual micro-stresses in the glass-ceramic abnormally increased with increasing the annealing time. The mechanical property degradation was attributed to the annealing-induced increase of the residual micro-stresses.

Additive manufacturing of fatigue resistant materials: Challenges and opportunities

This overview focuses on the current state of knowledge pertaining to the mechanical characteristics of metallic parts fabricated via additive manufacturing (AM), as well as the ongoing challenges and imminent opportunities in fabricating materials with increased fatigue resistance. Current experimental evidence suggests that the mechanical properties of laboratory AM specimens may not be representative of those associated with parts, due primarily to differences in geometry/size which influence the thermal histories experienced during fabrication, and consequently, microstructural features, surface roughness, and more. In addition, standards for mechanical testing methods, specimen design procedures, post-manufacturing treatments, etc., may need to be revised for AM parts. Standardizing the AM process may only be accomplished by strengthening the current understanding of the relationships among process parameters, thermal history, solidification, resultant microstructure, and mechanical behavior of the part. Having the ability to predict variations in mechanical behavior based on resultant microstructure, or matching the best conceivable properties of a part in accordance with the loading critical plane, are some possible solutions for making AM a more reliable means for producing functional parts. Developing microstructure-property models is arguably the first necessary step toward design optimization and the more efficient, accurate estimation of the structural integrity of AM parts.

Ex vivo testing of intact eye globes under inflation conditions to determine regional variation of mechanical stiffness.

BackgroundThe eye globe exhibits significant regional variation of mechanical behaviour. The aim of this present study is to develop a new experimental technique for testing intact eye globes in a form that is representative of in vivo conditions, and therefore suitable for determining the material properties of the complete outer ocular tunic.MethodsA test rig has been developed to provide closed-loop control of either applied intra-ocular pressure or resulting apical displacement; measurement of displacements across the external surface of the eye globe using high-resolution digital cameras and digital image correlation software; prevention of rigid-body motion and protection of the ocular surface from environmental drying. The method has been demonstrated on one human and one porcine eye globe, which were cyclically loaded. Finite element models based on specimen specific tomography, free from rotational symmetry, were used along with experimental pressure-displacement data in an inverse analysis process to derive the mechanical properties of tissue in different regions of the eye’s outer tunic.ResultsThe test method enabled monitoring of mechanical response to intraocular pressure variation across the surface of the eye globe. For the two eyes tested, the method showed a gradual change in the sclera’s stiffness from a maximum at the limbus to a minimum at the posterior pole, while in the cornea the stiffness was highest at the centre and lowest in the peripheral zone. Further, for both the sclera and cornea, the load–displacement behaviour did not vary significantly between loading cycles.ConclusionsThe first methodology capable of mechanically testing intact eye globes, with applied loads and boundary conditions that closely represent in vivo conditions is introduced. The method enables determination of the regional variation in mechanical behaviour across the ocular surface.

Variation of mechanical behavior of β-TCP/collagen two phase composite scaffold with mesenchymal stem cell in vitro

The primary aim of this study is to characterize the variational behavior of the compressive mechanical property of bioceramic-based scaffolds using stem cells during the cell culture period. β-Tricalcium phosphate (TCP)/collagen two phase composites and β-TCP scaffolds were fabricated using the polyurethane template technique and a subsequent freeze-drying method. Rat bone-marrow mesenchymal stem cells (rMSCs) were then cultured in these scaffolds for up to 28 days. Compression tests of the scaffolds with rMSCs were periodically conducted. Biological properties, such as the cell number, alkaline phosphatase (ALP) activity, and gene expressions of osteogenesis, were evaluated. The microstructural change due to cell growth and the formation of extracellular matrices was examined using a field-emission scanning electron microscope. The compressive property was then correlated with the biological properties and microstructures to understand the mechanism of the variational behavior of the macroscopic mechanical property. The porous collagen structure in the β-TCP scaffold effectively improved the structural stability of the composite scaffold, whereas the β-TCP scaffold exhibited structural instability with the collapse of the porous structure when immersed in a culture medium. The β-TCP/collagen composite scaffold exhibited higher ALP activity and more active generation of osteoblastic markers than the β-TCP scaffold.