Increase In Strain Energy Research Articles

Mechanical Properties of Modified Epoxy/Rubber Concrete

To research the effect of a elastic modifier on the mechanical properties of epoxy/rubber concrete, series of epoxy/rubber concretes were prepared with different elastic modifier content, the relationship between elastic modifier content and stress-strain curve of epoxy/rubber concretes were investigated. Results show: as the increase of elastic modifier content, both the compressive and bending stress-strain curves of epoxy/rubber concretes experience a stage transition of elastic-elastoplasticity-plastic apparently; the slope in the rising and falling section of stress-strain curves are gradually decreased; the peak stress decrease while the corresponding strain and stain energy increase. Content of elastic modifier between 40pbw and 60 pbw is proposed in order to attain better properties of epoxy/rubber concrete. Compared with ordinary concrete and rubberized concrete, Improved epoxy/rubber concrete has better comprehensive mechanical properties and larger rubber content.

Rockburst Generation in Discontinuous Rock Masses

We study rockburst generation in discontinuous rock masses using theoretical and numerical approaches. We begin by developing an analytical solution for the energy change due to tunneling in a continuous rock mass using linear elasticity. We show that the affected zone where most of the increase in elastic strain energy takes place is restricted to an annulus that extends to a distance of three diameters from the tunnel center, regardless of initial tunnel diameter, magnitude of in situ stress, and in situ stress ratio. By considering local elastic strain concentrations, we further delineate the Rockbursting Prone Zone found to be concentrated in an annulus that extends to one diameter from the tunnel center, regardless of original stress ratio, magnitude, and the stiffness of the rock mass. We proceed by arguing that in initially discontinuous rock masses shear stress amplification due to tunneling will inevitably trigger block displacements along preexisting discontinuities much before shear failure of intact rock elements will ensue, because of the lower shear strength of discontinuities with respect to intact rock elements, provided of course that the blocks are removable. We employ the numerical discrete element DDA method to obtain, quantitatively, the kinetic energy, the elastic strain energy, and the dissipated energy in the affected zone in a discontinuous rock due to tunneling. We show that the kinetic energy of ejected blocks due to strain relaxation increases with increasing initial stress and with decreasing frictional resistance of preexisting discontinuities. Finally, we demonstrate how controlled strain energy release by means of top heading and bench excavation methodology can assist in mitigating rockburst hazards due to stain relaxation.

Quantification of Adherence of Thermal Oxide Scale on Low Carbon Steel Using Tensile Test

In the present work, a tensile test method was used to investigate the adhesion of thermal oxide scale on low carbon steels oxidised in O2 containing 20 % H2O at 850 °C for up to 120 s. The mechanical adhesion energy was quantified, and a theoretical framework was developed to investigate the factors affecting the quantification i.e., the residual stress and Young’s modulus of the oxide scale. It was found that the quantified adhesion energies were in the range of 18–240 J m−2. When a higher value of the residual stress was used for the quantification, the quantified mechanical adhesion energy was decreased to a critical value and afterwards turned to be higher because of the increased strain energy accumulated in the oxide due to the stress in the direction perpendicular to the tensile loading. Furthermore, when a higher value of Young’s modulus of the oxide was used for the quantification, a higher quantified mechanical adhesion energy was obtained.

Effect of ruthenium on the precipitation of topologically close packed phases in Ni-based superalloys of 3rd and 4th generation

The precipitation of topologically close packed (TCP) phases is detrimental for the high temperature strength of high refractory Ni-based superalloys. The beneficial influence of Ru with respect to this so called instability is nowadays well accepted. In the present paper the precipitation of topologically close packed (TCP) phases is studied quantitatively in two experimental alloys (one Ru-free and one with addition of Ru) to clarify the mechanism of the Ru effect. It is confirmed that the TCP phase precipitates undergo sequential phase transformation with the tetragonal σ-phase precipitating first. Ru retards the phase transformation and leads to decreased equilibrium volume fraction of TCP phases. The results clearly indicate that Ru decreases the driving force for TCP phase precipitation. Investigations of crystallography and chemistry of the TCP/matrix interface point to an additional effect by increase of misfit strain energy.

Regularities of the contact interaction of double carbides (Ti1 − n Me n )C with nickel

Regularities of metallurgical reactions of titanium carbide alloyed with Group IV–VI transition metals with the nickel melt are generalized. It is established that the interaction of double carbides with nickel is characterized by the preferential dissolution of carbon and alloying metal in it. Correspondingly, the composition of the carbide phase varies. It is shown that the efficiency of the influence of alloying elements on the dissolution rate of titanium carbide in nickel depends on the ratio of atomic sizes of titanium and alloying metal. If RMe > RTi (Me = Zr, Hf), the interaction intensity between titanium carbide and nickel increases, and if RMe ≤ RTi (Me = V, Nb, Mo, W), it decreases. In the first case, the determining factor is an increase in elastic strain energy of the lattice and, in the second case, it is a decrease in the interphase energy of the carbide-melt interface.

Regularities of contact interaction of double (Ti1–nMen)С carbides with nickel

The regularities of metallurgical reactions of IV-VI group transition metal alloyed titanium carbide with nickel melt are generalized. Interaction of dou- ble carbides with nickel is established to be characterized by primary dissolution of carbon and alloying metal in it. Accordingly the carbide phase composition varies. The efficiency of effect of alloying elements on titanium carbide dissolution rate in nickel depends on the atomic dimensional re- lationship of titanium and alloying metal. If R Me > R Ti (Me = Zr, Hf ), the intensity of titanium carbide interaction with nickel increases; if R Me ≤ R Ti (Me = V, Nb, Mo, W), then it decreases. In the first case the defining factor is the increase in elastic strain energy of the lattice; in the second case – the decrease of interphase energy of the carbide-melt interface.

An effective stacking fault energy viewpoint on the formation of extended defects and their contribution to strain hardening in a Fe–Mn–Si–Al twinning-induced plasticity steel

A deformation-dependent stacking fault energy (SFE) viewpoint is invoked to interpret the low strain rate tensile deformation of a Fe–27Mn–2.5Si–3.5Al austenitic steel at room temperature by using X-ray diffraction analyses and transmission electron microscopy (TEM) observations. The effective SFE of austenite increased with strain from ∼18 to 40mJm−2, and it was reasoned that this was the result of the increase in strain energy of the stacking faults (SFs) per unit area due to its dependence on the dislocation character and density. Twinning was observed at 2% strain and confirmed to occur by a glide mechanism of a6〈121〉 Shockley partial dislocations, leading to the formation of overlapping intrinsic–extrinsic SF pairs representing a three-layer twin embryo, revealing periodic dislocation contrast in TEM. The early onset of twinning is attributed to the unusually low critical twinning stress of the steel, ∼200MPa. In spite of twinning, the stacking fault probability (Psf) of twinned austenite was remarkably low (∼10−4) at low strains, but increased moderately (to ∼10−3) up to failure strain. At the emergence of twinning, the corresponding perfect dislocation density was low (∼1014m−2) but was well above the critical dislocation density required for twinning occurrence. Dislocation character analysis indicated that increasing deformation gradually changed the dislocation character from edge to screw type. The microstructural parameters of the steel estimated in direct or indirect relation to its SFE could explain its flow stress and strain hardening behavior.

Ti resetting in quartz during dynamic recrystallization: Mechanisms and significance

The ubiquity of quartz in continental crust, and the involvement of SiO2 in multiple metamorphic processes such as reactions, fluid flux, and solution-transfer processes, makes quartz an obvious choice for reconstructing prograde metamorphic conditions in various rock types. Recent studies have shown the usefulness of analyzing Ti distribution in quartz to constrain pressure-temperature-(relative) timedeformation (P-T-t-D) in metamorphosed tectonites. New high-precision single-crystal X‑ray diffraction volume constraints on Ti-doped and chemically pure quartz provide further evidence for substitution of Ti 4+ for Si 4+ in the tetrahedral site in quartz, with resultant lattice strain on the structure. Recent applications of the Ti-in-quartz thermobarometer to dynamically recrystallized quartz have identified recrystallized subgrains that contain lower Ti concentrations ([Ti]) than their host porphyroclasts. In addition, [Ti] are lower than expected for the temperatures of recrystallization. Atomistic simulations that estimate energetic perturbations resulting from Ti incorporation into the quartz lattice indicate that significant increases in strain energy occur only at very high [Ti]; the strain-energy increase is negligible for [Ti] typical of quartz grown under mid-crustal conditions. This suggests that lattice strain rarely provides an appreciable driving force for Ti loss from quartz; instead, it appears that subgrain boundaries and dislocation arrays migrating through recrystallizing quartz crystals can promote localized re-equilibration, thermodynamically regulated by the composition of the intergranular medium (typically undersaturated in Ti). It therefore appears that analyses from dynamically recrystallized quartz cannot be meaningfully interpreted until methods are developed that can account quantitatively for the reduction of Ti resulting from crystal plastic flow.

Work and Tension: New Evidence that Adherent Cells of the Same Area Do the Same Work Independent of Stiffness and Focal Adhesions

Work and Tension: New Evidence that Adherent Cells of the Same Area Do the Same Work Independent of Stiffness and Focal Adhesions

Strain energy in the femoral neck during exercise

Physical activity is recommended to mitigate the incidence of hip osteoporotic fractures by improving femoral neck strength. However, results from clinical studies are highly variable and unclear about the effects of physical activity on femoral neck strength. We ranked physical activities recommended for promoting bone health based on calculations of strain energy in the femoral neck. According to adaptive bone-remodeling theory, bone formation occurs when the strain energy (S) exceeds its homeostatic value by 75%. The potential effectiveness of activity type was assessed by normalizing strain energy by the applied external load. Tensile strain provided an indication of bone fracture. External force and joint motion data for 15 low- and high-load weight-bearing and resistance-based activities were used. High-load activities included weight-bearing activities generating a ground force above 1 body-weight and maximal resistance exercises about the hip and the knee. Calculations of femoral loads were based on musculoskeletal and finite-element models. Eight of the fifteen activities were likely to trigger bone formation, with isokinetic hip extension (ΔS=722%), one-legged long jump (ΔS=572%), and isokinetic knee flexion (ΔS=418%) inducing the highest strain energy increase. Knee flexion induced approximately ten times the normalized strain energy induced by hip adduction. Strain and strain energy were strongly correlated with the hip-joint reaction force (R2=0.90–0.99; p<0.05) for all activities, though the peak load location was activity-dependent. None of the exercises was likely to cause fracture. Femoral neck mechanics is activity-dependent and maximum isokinetic hip-extension and knee-flexion exercises are possible alternative solutions to impact activities for improving femoral neck strength.

Wedge disclination dipole in an embedded nanowire within the surface/interface elasticity

AbstractThe elastic behavior of an arbitrary oriented wedge disclination dipole located inside a nanowire, which in turn is embedded in an infinite matrix, is studied within the surface/interface theory of elasticity. The corresponding boundary value problem is provided using complex potential functions. The potential functions are defined through modeling the wedge disclination in terms of an equivalent distribution of edge dislocations. The interface effects on the stress field and strain energy of the disclination dipole and image forces acting on it, the influence of relative shear moduli of the nanowire and the matrix, as well as the different characteristics of the interface are studied thoroughly. It is shown that the positive interface modulus leads to increased strain energy and extra repulsive forces on the disclination dipole. The noticeable effect of the negative interface modulus is the non-classical oscillations in the stress field of the disclination dipole and an extra attractive image force on it.

Coarsening behavior of γ′ and γ″ phases in GH4169 superalloy by electric field treatment

The coarsening behaviors of γ′ and γ″ phases in GH4169 alloy aged at 1023 and 1073 K with electric field treatment (EFT) were investigated by transmission electron microscopy (TEM) and positron annihilation lifetime spectroscopy (PALS). It is demonstrated that precipitation coarsening occurs, and the growth activation energies of γ′ and γ″ phases can be decreased to 115.6 and 198.1 kJ·mol−1, respectively, by applying the electric field. The formation of a large number of vacancies in the matrix is induced by EFT. Due to the occurrence of vacancy migration, the diffusion coefficients of Al and Nb atoms are increased to be 1.6–5.0 times larger than those without EFT at 1023 or 1073 K. Furthermore, the formation of vacancy clusters is promoted by EFT, and the increase in strain energy for the coarsening of γ′ and γ″ phases can be counterbalanced by the formation of vacancy clusters.

Finite element analysis on longitudinal and radial functionally graded femoral prosthesis

This study focused on developing a 3D finite element model of functionally graded femoral prostheses to decrease stress shielding and to improve total hip replacement performance. The mechanical properties of the modeled functionally graded femoral prostheses were adjusted in the sagittal and transverse planes by changing the volume fraction gradient exponent. Prostheses with material changes in the sagittal and transverse planes were considered longitudinal and radial prostheses, respectively. The effects of cemented and noncemented implantation methods were also considered in this study. Strain energy and von Mises stresses were determined at the femoral proximal metaphysis and interfaces of the implanted femur components, respectively. Results demonstrated that the strain energy increased proportionally with increasing volume fraction gradient exponent, whereas the interface stresses decreased on the prostheses surfaces. A limited increase was also observed at the surfaces of the bone and cement. The periprosthetic femur with a noncemented prosthesis exhibited higher strain energy than with a cemented prosthesis. Radial prostheses implantation displayed more strain energy than longitudinal prostheses implantation in the femoral proximal part. Functionally graded materials also increased strain energy and exhibited promising potentials as substitutes of conventional materials to decrease stress shielding and to enhance total hip replacement lifespan.

Concrete behaviour in direct tension tests at high strain rates

Direct tensile tests on cubic concrete specimens of 60 mm side were performed at strain rates from 1 s−1 to 10 s−1 by means of a modified Hopkinson bar. The results of 26 such high strain rate tests on two concrete types, with 5 and 10 mm maximum aggregate size, are presented in this paper. As reference for these dynamic tests, a series of 14 static tests with specimens of the same geometry was also carried out. The experiments show a significant increase in tensile strength, failure strain, elastic modulus and fracture energy as the strain rates increase. The dynamic results obtained are compared with data and formulations present in the literature, the validity of which is critically assessed. Deviations or knowledge gaps are identified, which confirm the need to generate new data in order to develop more accurate formulae able to predict the evolution of mechanical properties with increasing strain rate.

Evolution of strain energy during recrystallization of plated Cu films

The microstructural evolution within plated Cu films has been investigated using high-resolution x-ray diffraction, revealing a change in strain state within the recrystallized grains and the surrounding matrix with time. By approximating the case of an isolated grain in a randomly textured material as an Eshelby inclusion in an elastically isotropic matrix, we can determine the elastic strain energy in addition to the interaction strains that develop within the grain due to the effects of elastic anisotropy. The elastic strain energy density generated by a grain possessing cubic symmetry with arbitrary orientation within an elastically isotropic matrix has been compared to that within a fiber-textured film, revealing that the former case possesses less strain energy. These results suggest that the recrystallization of Cu (111) grains from an electroplated film with a small, initial grain size is less energetically favorable for films exhibiting strong (111) texture than for a randomly textured film. Experimental results indicate a sequence that emerges during the recrystallization process: (111) grains grow first, suggesting that the decrease in surface energy provided by the (111) surfaces is larger than the increase in elastic strain energy created by (111) grains. For sufficiently thick films, (100) grains emerge, lowering the strain energy density in the film, after (111) grain growth has saturated because no further decrease in energy is supplied by (111) surface growth. By examining plated Cu films of different thicknesses, we correlate the appearance of recrystallized (100) grains with a threshold energy density based on the additional energy associated with (100) surfaces relative to (111) surfaces.

Transverse cracking of a simple lap joint under axial load

The failure mode of axially loaded simple, single lap joints formed between thin adherends which are flexible in bending is conventionally described as one of axial peeling. We have observed – using high-speed photography – that it is also possible for failure to be preceded by the separation front, or crack, moving in a transverse direction, i.e. perpendicular to the direction of the axial load. A simple energy balance analysis suggests that the critical load for transverse failure is the same as that for axial separation for both flexible lap joints, where the bulk of the stored elastic energy lies in the adhesive, and structural lap joints in which the energy stored in the adherends dominates. The initiation of the failure is dependent on a local increases in either stress or strain energy to some critical values. In the case of a flexible joint, this will occur within the adhesive layer and the critical site will be close to one of the corners of the joint overlap from which the separation front can proceed either axially or transversely. These conclusions are supported by a finite element analysis of a joint formed between adherends of finite width by a low modulus adhesive.

Selective surface functionalization at regions of high local curvature in graphene

Monolayer graphene was deposited on a Si wafer substrate decorated with SiO(2) nanoparticles (NPs) and then exposed to aryl radicals that were generated in situ from their diazonium precursors. Using micro-Raman mapping, the aryl radicals were found to selectively react with the regions of graphene that covered the NPs. The enhanced chemical reactivity was attributed to the increased strain energy induced by the local mechanical deformation of the graphene.

An Epitaxial Model for Heterogeneous Nucleation on Potent Substrates

In this article, we present an epitaxial model for heterogeneous nucleation on potent substrates. It is proposed that heterogeneous nucleation of the solid phase (S) on a potent substrate (N) occurs by epitaxial growth of a pseudomorphic solid (PS) layer on the substrate surface under a critical undercooling (ΔT c). The PS layer with a coherent PS/N interface mimics the atomic arrangement of the substrate, giving rise to a linear increase of misfit strain energy with layer thickness. At a critical thickness (h c), elastic strain energy reaches a critical level, at which point, misfit dislocations are created to release the elastic strain energy in the PS layer. This converts the strained PS layer to a strainless solid (S), and changes the initial coherent PS/N interface into a semicoherent S/N interface. Beyond this critical thickness, further growth will be strainless, and solidification enters the growth stage. It is shown analytically that the lattice misfit (f) between the solid and the substrate has a strong influence on both h c and ΔT c; h c decreases; and ΔT c increases with increasing lattice misfit. This epitaxial nucleation model will be used to explain qualitatively the generally accepted experimental findings on grain refinement in the literature and to analyze the general approaches to effective grain refinement.

Fracture Toughness of Laminated Composites – A Non-Linear Analysis

Non-linear fracture behaviour of laminated composite materials under mode I (crack opening) loading conditions was studied experimentally and theoretically. For this purpose, single edge notched tension (SENT) tests were carried-out using displacement-controlled loading under room temperature dry conditions. It was found that the load-displacement diagram had non-linear character prior to onset of macroscopic crack propagation. Thus, the main objective of this paper was to study the fracture properties using non-linear fracture mechanics. A two-dimensional finite element model was set-up in order to analyze the non-linear response of the SENT test specimen. Non-linear deformation due to damage was simulated using the Tsai-Hill failure criterion. The failure analysis revealed that the damage was localized in the vicinity of the crack tip. The fracture response was characterized using a J-integral. It was shown that a realistic appraisal of the potential for crack growth should include the effects of non-linear material deformation. It was found that taking into account the non-linear deformation increased the fracture resistance. This finding was attributed to the increased strain energy dissipation due to the damage induced non-linear behaviour of the SENT test specimen.

Bio-nanomechanical Detection of Diabetic Marker HbA1c

We report the development of an ultrasensitive immunosensor system for the detection of specific diabetic biomarker glycated hemoglobin (HbA1c) using specific antibody functionalized micromechanical cantilever chips. The biomolecules-induced deflection of the cantilever beam reflects the interplay between the strain energy increase of the cantilever and the free energy reduction of the interaction, providing a unique system for investigating the connection between the nanomechanics and the chemistry of antibody–antigen interaction at very low concentration. Cantilevers were functionalized with specific antibodies using site-directed antibody immobilization technique which was adopted to attach antibody on to the gold substrate. The antibody immobilized cantilevers were used to detect the level of the expressed biomarker in standard samples by adopting direct immunoassay format without using any labels. The assay exhibited an excellent sensitivity for HbA1c in the dynamic range from 0.147 to 1.47 pM. This label-free detection method could be used for fast, high-throughput screening of specific biomarkers for the therapeutic management of diabetes mellitus in clinical diagnostic at a very low cost.