Compressive Normal Stress Research Articles

A complex stress-induced dislocation core reconstruction of an edge dislocation on the first pyramidal plane in magnesium and its abnormal dislocation mobility

The effect of the complex stress on the mobility of an edge dislocation on the first pyramidal plane in magnesium is investigated through molecular dynamic simulation (MDs). A novel dislocation with greatly improved mobility is obtained by applying the combined compressive normal stress and shear. The Peierls stress of the new dislocation is reduced to less than a tenth of the original and the mobility factor increases almost twice. Based on the analyses of atomic configuration and the energy barrier of vacancy formation, the mobility improvement is ascribed to the dislocation core reconstruction and its related dissociation. These new findings are also validated in other HCP metals e.g. Ti and Zr.

The thermal responses of composite box girder bridges with corrugated steel webs under solar radiation

Owing to the direct exposure to complex atmospheric environments, the temperature field of composite box girder bridge with corrugated steel webs (CBGB-CSW) is likely non-uniformly distributed. Whereas, the current researches regarding the thermal responses of CBGB-CSW are insufficient, and the thermal responses of CBGB-CSW under solar radiation are still unknown. Therefore, this paper conducted a long-term temperature experiment on a scaled model to explore the temperature distribution characteristics in CBGB-CSW. Meanwhile, a three-dimensional thermal–mechanical coupling Finite Element (FE) model is established to simulate the temperature field in the experiment girder. The accuracy and effectiveness of the developed FE model has been verified by the measured temperature data. Therewith, the thermal responses (i.e., stress and displacement) of a full-scale continuous CBGB-CSW with a span of 150 m are numerically investigated. The results indicate that the maximum stresses always occur at the midspan section (with a depth of 5 m) of the continuous CBGB-CSW, and considerable concentrations of stress are observed in the steel-concrete junction. The maximum longitudinal tensile and compressive normal stresses within 0.4 m of the upper junction can reach 5.55 MPa and −8.46 MPa respectively, and those of the lower junction can reach 6.96 MPa and −7.05 MPa respectively. Besides, owing to the impacts of vertical and horizontal temperature gradients, significant displacements of the whole bridge can also be observed. The maximum vertical displacement (5.33 mm) of the CBGB-CSW is estimated at the top plate in the midspan, while the maximum horizontal displacement (0.74 mm) is estimated at the trough of the southern corrugated steel web in the midspan. Notably, the outcomes of this paper can provide some useful references for engineers and scholars to understand the thermal responses of the CBGB-CSW.

Stress-strain state of ceramic shell mold during formation of spherical steel casting in it. Part 2

The paper presents the results of numerical calculations of the solution to the problem of modeling the process of possible cracking in a spherical shell mold when pouring liquid steel into it and cooling the solidifying casting. The numerical scheme of the axisymmetric problem and the algorithm for its solution were given in Part 1. The crack resistance is estimated by magnitude of the normal stresses in the ceramic shell during its co-cooling with a solidifying casting. The results detailed analysis considered: fields of displacement, stresses, and temperatures both on spherical surface and in growing crust of solidified metal. The solution took into account the change in the shear modulus of the mold material from temperature, and an assessment of this refinement was given. The problem was solved in two ways. The first – with a constant shift modulus of the shell mold; the second – with its temperature-dependent shift modulus. There is a significant difference between these variants in terms of magnitude of the normal stresses arising in the shell mold. The authors analyzed resistance of the shell mold spherical geometry to external influences from its support filler and filling funnel. The problem of determining the contact and free surfaces at the boundary of the shell mold and support filler was solved. The results are presented graphically in the form of diagrams of stresses and temperatures over the studied area in its different sections and time intervals for cooling of the growing metal crust. The role of compressive normal stresses σ22 , σ33 on the surface of contact of the shell mold with liquid metal at the initial moment of cooling on probability of cracking in a spherical mold is shown. The level of strain-stress state in a spherical shell mold when cooling a steel casting in it is significantly determined by dependence of shift modulus of the shell mold on temperature.

Spatio-temporal evolution law of anisotropic shear damage on rock mass joint surface affected by joint morphology

The spatial–temporal evolution law of shear damage on the joint surface is closely related to its morphological characteristics. Understanding the heterogeneous failure behavior of the joint surface is essential for revealing the controlling role of the joint morphology. The diorite from the Guanshan Tunnel is investigated through anisotropic direct shear tests in this study. Based on shear damage quantification and acoustic emission (AE) localization techniques, the heterogeneous damage evolution law of joint surfaces under different joint compression strength (JCS), normal stress (σn), and morphology parameter (M) is studied. The results indicate that the joint surface morphology, shear damage, and AE parameters exhibit similar anisotropic characteristics in different shear directions. An increase in the morphology parameter leads to an increase in shear failure, with shear fracture energy and the number of fracture events showing an increasing trend. Meanwhile, the occurrence of a large number of fracture points shifts from the pre-peak nonlinear period to the post-peak period. However, the evolution process of fracture events exhibits certain similarities, though the morphology parameters are different in two opposite shear directions. Additionally, shear damage volume and fracture energy demonstrate consistency in spatial distribution and quantitative characteristics, while the linear scale factor between cumulative shear fracture energy and damage volume decreases with increasing joint surface strength. These findings assist in a better understanding of the anti-sliding property of joint surfaces and provide crucial clues for further exploration of joint surface failure mechanisms.

Mandibular biomechanics rehabilitated with different prosthetic restorations under normal and impact loading scenarios

BackgroundRestorative treatment options for edentulous patients range from traditional dentures to fixed restorations. The proper selection of materials greatly influences the longevity and stability of fixed restorations. Most prosthetic parts are frequently fabricated from titanium. Ceramics (e.g. zirconia) and polymers (e.g. PEEK and BIOHPP) have recently been included in these fabrications. The mandibular movement produces complex patterns of stress and strain. Mandibular fractures may result from these stresses and strains exceeding the critical limits because of the impact force from falls or accidents. Therefore, it is necessary to evaluate the biomechanical behavior of the edentulous mandible with different restorations under different loading situations.ObjectiveThis study analyzes the biomechanical behavior of mandibles after four prosthetic restorations for rehabilitation under normal and impact loading scenarios.Material and MethodsThe mandibular model was constructed with a fixed restoration, which was simulated using various materials (e.g. Titanium, Zirconia & BIOHPP), under frontal bite force, maximum intercuspation, and chin impact force. From the extraction of tensile and compressive stresses and strains, as well as the total deformation of mandible segments, the biomechanical behavior and clinical situations were studied.ResultsUnder frontal bite, the anterior body exhibited the highest tensile (60.34 MPa) and compressive (108.81 MPa) stresses using restoration 4, while the condyles and angles had the lowest tensile (7.12 MPa) and compressive (12.67 MPa) stresses using restoration 3. Under maximum intercuspation, the highest tensile (40.02 MPa) and compressive (98.87 MPa) stresses were generated on the anterior body of the cortical bone using restoration 4. Additionally, the lowest tensile (7.7 MPa) and compressive (10.08 MPa) stresses were generated on the condyles and angles, respectively, using restoration 3. Under chin impact, the highest tensile (374.57 MPa) and compressive (387.3 MPa) stresses were generated on the anterior body using restoration 4. Additionally, the lowest tensile (0.65 MPa) and compressive (0.57 MPa) stresses were generated on the coronoid processes using restoration 3. For all loading scenarios, the anterior body of the mandible had the highest stress and strain values compared with the other segments. Compared to the traditional titanium restoration.2, restoration.1(zirconia) increases the tensile and compressive stresses and strains on the mandibular segments, in contrast to restoration.3 (BIOHPP). In addition, zirconia implants exhibited higher displacements than the other implants.ConclusionIn the normal loading scenario, the tensile and compressive stresses and strains on the mandible were within the allowable limits when all restorations were used. Under the chin impact loading scenario, the anterior body of the mandible was damaged by restorations 1 and 4.

Effect of deposition rate and annealing on Nb thin film growth on Cu substrate: Molecular dynamics simulation

Molecular dynamics (MD) simulations are performed to study the growth mechanisms of Nb thin film on Cu substrate. In this investigation, we provide insights and information about the quality of the deposited Nb thin film by analyzing the growth mode, stress, and evolution of its microstructural and morphological properties by considering different deposition rates and thermal annealing processes. The results show that the growth of Nb atoms on the Cu substrate follows the island mode. The interface analysis reveals the presence of a nucleation phenomenon, moreover, the results indicate that the first layer of Nb film remains incomplete until approximately the amount of 4 monolayers of Nb is deposited. The analysis of interdiffusion indicates that Nb penetration is initially limited to the first Cu layer. However, after annealing, there is a significant increase in Nb atom penetration and a clear rearrangement of Nb within each layer of the film. The film adopts a BCC structure, with crystallinity rates varying based on the deposition rate. The highest crystallinity rate is observed at 5 atoms/ps, and annealing further increases these percentages. Deposition at different rates leads to different levels of compressive normal and biaxial stress.

Coarse-Grained Molecular Dynamics Simulations of Nanoscale Roughness Effects on Oil Film Delamination

In boundary lubrication, the detachment of lubricant molecules from a solid surface is likely to occur due to the presence of high compressive normal stress combined with shear stress exerted on the solid–liquid interface. This phenomenon often results in a delamination behavior at the interface. We aim to investigate the nanoscale roughness effect on the oil film delamination from sliding iron surfaces with grain boundaries by coarse-grained molecular dynamics simulations. As a result, the oil film delamination was effectively suppressed in higher roughness. Two distinct mechanisms of delamination were found depending on surface roughness when the critical normal stress is exceeded. High roughness enhanced the ability to prevent complete slip but had negligible influence on partial slip.Graphical

Investigation of the effect of anisotropy on Generalized Forming Limit Diagram

In contemporary industrial practices, various methods are employed to subject raw metal sheets to deformation in order to fabricate requisite components. These sheets exhibit a defined capacity for deformation during the forming process. Over recent decades, a plethora of experimental and numerical methodologies have emerged to ascertain these forming limits. Initially, a forming limit diagram (FLD) was devised, predicated on the phenomenon of necking, under the assumption that forming takes place under plane-stress conditions. However, in certain complex processes like hydroforming and incremental forming, necking can manifest at sites where normal and through-thickness shear stresses act upon the sheet in addition to the in-plane stresses, rendering the plane-stress assumption inadequate for predicting forming limits in such scenarios. Thus, it becomes imperative to derive a diagram that can accurately forecast forming limits in these processes. This study aims to establish a Generalized Forming Limit Diagram (GFLD) through numerical means. GFLDs were constructed utilizing two distinct yield functions, namely Von-Mises and Hill48, for isotropic and anisotropic states, respectively. The findings reveal that normal compressive stress and through-thickness shear strain augment the formability of sheet metals. Furthermore, the outcomes illustrate that accounting for anisotropy introduces variances between diagrams in some regions of the FLD curve while the discrepancies are minor within the central regions.

Experimental study on nonlinear flow behavior in smooth and rough sandstone fractures subjected to various injection pressure and normal compressive stress

Experimental study on nonlinear flow behavior in smooth and rough sandstone fractures subjected to various injection pressure and normal compressive stress

Experimental Study and Mechanism Analysis on Compression–Shear Behavior of Hydraulic Asphalt Concrete at Different Temperatures

Abstract Hydraulic asphalt concrete (HAC), typically employed as an impermeable structure in embankment dams, is increasingly recognized for its widespread engineering applications. However, investigations of the mechanical performance of HAC under combined compressive–shear stress remain limited, particularly given its temperature sensitivity. Therefore, this study investigates the mechanical behaviors of HAC under combined compressive–shear stress at diverse temperatures and normal compressive stresses. Specifically, the failure modes, stress–strain curves, peak shear stress, and strain of HAC under various temperatures and normal compressive stresses are obtained for analysis. Experimental results demonstrate that the combination of normal compressive stress and temperature induces changes in peak shear stress and correlated shear strain. Increased normal compressive stress results in vertical restriction and the emergence of horizontal cracks, with deformation amplifying at elevated temperatures. All failure modes of HAC under these conditions are absent of spalled fines and debris. It is observed that as the normal compressive stress increases, the peak shear stress progressively increases, whereas an increase in temperature yields a clear decrease in peak shear stress. The shear strength of HAC comprises the cohesion strength of the asphalt matrix and the interfacial adhesion strength between aggregates and asphalt. Finally, three modified compressive–shear failure criteria that exhibit good prediction accuracy are established for HAC at diverse temperatures. This research offers a theoretical reference for the future investigation and engineering application of HAC.

ВЛИЯНИЕ ТОЛЩИНЫ ПОПЕРЕЧНОГО И ПРОДОЛЬНЫХ СЛОЕВ НА ДЕФОРМАЦИИ И НАПРЯЖЕНИЯ В 3-СЛОЙНОЙ ПЛИТЕ ДПК (CLT), СМОДЕЛИРОВАННОЙ КАК СОСТАВНАЯ ПЛАСТИНА

The study examines the effect of the transverse and longitudinal layers thickness of a three-layer CLT panel on the deformations and distribution of the resulting tensile and compressive normal stresses in the layers. Due to the current lack of a unified methodology for the calculation of multilayer materials with orthotropic properties in layers at present, we carried out the study with the SCAD+ computing complex using the finite element method. The studied model was a composite orthotropic plate. The authors obtained, systematized and clearly showed the dependences of the values of the maximum deflection and normal stresses on the thickness variation of transverse and longitudinal lamellae in a three-layer CLT panel under different boundary conditions. As a result of the study, we found that the greatest influence on the deflection and normal stresses along the span was caused by the longitudinal slab layers. The results provide a better insight into the relationship between deformability and stress distributions and the variation of transverse and longitudinal layer thicknesses. The obtained patterns can be used in the design of building structures using CLT panel.

Anchors to Solid Clay Brick Masonry in Tension: Behavior under Monotonic and Repeated Loading for Constant Embedment Depth

This paper presents a part of an extensive experimental campaign performed at the National Technical University of Athens (NTUA) with the purpose of investigating the behavior of chemical anchors embedded in solid brick masonry. Anchors are tested in tension under monotonic or repeated loading. All tests are performed under displacement-controlled conditions. The experimental setup and the instrumentation are presented, along with the investigated parameters and the rationale for the selection of the values of those parameters. In this part of the experimental work, comprising fifty-six (56) tests, the examined parameters are the anchor locations (in mortar joints and in the center of bricks), the state of the substrate (cracked or uncracked), the width of the crack crossing the anchor or at its vicinity (up to 1.20 mm), as well as the loading history (monotonic or repeated). In the tests presented herein, the embedment length of the anchors is equal to 100 mm. The anchors are embedded in solid brick masonry wallettes, and subjected to a normal compressive stress equal to 0.20 MPa. The observed failure modes are explained, and the overall behavior of anchors subjected to tension is presented and commented upon, along with the effect of the investigated parameters on the measured tension resistance, and on the corresponding displacement.

Effect of Contact Pressure on Strain Distribution during Compression-Type Bulk Forming Processes.

Inhomogeneity of the material properties of workpieces developed during compression-type bulk forming processes (CBFPs) is an important issue. The effect of contact pressure on the workpiece surface on the strain inhomogeneity in the workpiece was investigated to understand and reduce the formation of strain inhomogeneity during CBFPs. Workpieces fabricated via rod caliber rolling, rod flat rolling, plate flat rolling, and rod compression were analyzed and compared. The extent of strain inhomogeneity in a workpiece differs with the forming process, because the occurrence of macroscopic shear bands (MSBs) is dependent on the workpiece shape and tool design. A flat-rolled rod exhibits the maximum strain inhomogeneity, whereas a flat-rolled plate shows the minimum strain inhomogeneity. The occurrence of MSBs was influenced by the distribution of the normal contact pressure or compression stress. The MSBs were stronger when the contact pressure was higher in the edge region of the surface. For example, the flat-rolled plate exhibited weak MSBs due to the relatively uniform or higher contact pressure on the central region. In contrast, strong MSBs appeared in the flat-rolled rod and compressed rod, because the contact pressure in the edge region of these two processes was high. Thus, the strain inhomogeneity in a workpiece fabricated via CBFPs can be reduced by controlling the contact pressure distribution on the workpiece surface.

On the influence of tool contact stress on tensile instabilities in plane strain stretching and bending of sheet metals

It is well known that the widely used forming limit curve (FLC) based upon in-plane stretching fails to account for the delay in plastic instability in the presence of appreciable bending and tool contact pressure. The recently proposed General Incremental Stability Criterion (GISC) – a generalization of the Modified Maximum Force Criterion (MMFC) to triaxial loading – revealed the dependence of the boundary conditions on the formation of tensile instabilities. Nevertheless, it remains unclear how the combined effect of radial bending stresses and tool contact pressure affects the formation of an acute neck. It is shown in this study that a compressive normal stress causes a shift of the strain state from initial plane strain tension to positive minor strains for material layers within the cross-section. The convex (outer) layer remains in a state of plane strain-plane stress. Accounting for the shift in the strain state is key to capture the dependence of the contact pressure on necking. A simplified modelling approach, which enforces plane strain tension of the cross-section, was able to capture the formability gain due to bending but failed to account for the delay in plastic instability due to the contact pressure. An incremental multi-layer model was required to account for non-monotonic loading due to bending over the punch and the biaxial shift in the strain path caused by the contact pressure. The models were then applied to the experimental forming limits of a 3rd Gen 1180 advanced high strength steel to demonstrate the formability gains under triaxial loading due to the contact pressure.

Nonlinear flow and permeability anisotropy characteristics in hydraulic fracturing-induced rock fractures subjected to various normal compressive stresses

Well productivity after hydraulic fracturing is strongly affected by the flow behaviors in created fracture complexity. In this study, gas flow tests were conducted in splitting fractures (induced by Brazilian splitting) and hydraulic fractures (created by hydraulic fracturing) to study the nonlinear fluid flow behaviors in rough fractures. 3D fracture surfaces were first digitally reproduced with a scanner and then the fracture geometry parameters (roughness profile index R_{p}, the root mean square of the fracture profile wall slope Z_{2}), aperture distributions were computed for both fractures. The influence of the fracture geometry characteristics on the nonlinear flow behaviors were systematically analyzed. The permeability anisotropy was numerically examined in detail. The results show that R_{p}, Z_{2} and mean aperture of hydraulic fractures are relatively smaller, indicating that the fracture surfaces are smoother. The transmissivity of splitting fracture is relatively higher than that of hydraulic ones, and the ratio of splitting to hydraulic one varies from 2.51 at sigma_{c} = 1 MPa to 60.95 at sigma_{c} = 40 MPa. By contrast, splitting fractures have larger critical Reynolds number and lower critical pressure gradient, implying that nonlinearity is easier to occur in splitting fractures. The average Forchheimer coefficient for splitting fractures is 0.00577, which is 1.5 times larger than that (0.0041) for hydraulic ones. In addition, the fractures exhibit strong permeability anisotropy and this anisotropic effect is significantly dependent on the loading stress. In general, the permeability anisotropy in hydraulic fracture is more significant, showing that their permeability anisotropy ratios K are larger and more sensitive to the loading. The obtained results confirm that there exist some discrepancies in flow behaviors between splitting and hydraulic fractures and for more accurate evaluation in engineering practice, hydraulic fractures should be fully considered.

A Low-Stress Method for Determining Static and Dynamic Material Parameters for Vibration Isolation with the Use of VMQ Silicone.

Progressive urbanisation causes building users to be affected by increasing amounts of noise and vibrations that come from transportation and other building users. This article presents a test method that can be used to identify quantities of methyl vinyl silicone rubber (VMQ) necessary to carry out solid mechanics finite element method simulations such as Young's modulus, Poisson ratio, and damping parameters. These parameters are necessary to model the vibration isolation used for protection against noise and vibration. The article uses an original combination of dynamic response spectrum and image processing methods to determine these quantities. The tests were carried out using one machine for the range of normal compressive stresses of 64-255 kPa with cylindrical samples of various shape factors in the range of 1-0.25. The parameters for the simulation of solid mechanics in statics were obtained from image processing based on the deformation of the sample under load; for dynamic solid mechanics, the parameters were obtained from the response spectrum of the tested system. The article shows the possibility of determining the given quantities using the original method of the synthesis of dynamic response and FEM-supported image analysis, which states the article's novelty. Additionally, limitations and preferred ranges of sample deformation in terms of load stress and shape factor are presented.

Study of stress intensity factors in sliding and tearing modes for subsurface elliptical cracks in rolling train wheels

AbstractIn the railway systems, induced contact between wheels and rails creates maximum shear stress around the contact surfaces. These shear stresses vary with the wheel's rolling and can initiate and extend subsurface cracks in the wheel and rail. The most common subsurface cracks in the rail systems have elliptical forms. Sliding and tearing modes of the fracture can be observed due to different components of the shear stresses around the contact area. Compressive normal stress has no considerable effects on in‐plane and out‐of‐plane shear modes for subsurface cracks. In this research, by proper modeling of the wheel and rail, the effects of dimensions, position, and depth of the subsurface cracks on the stress intensity factors of the sliding (KII) and tearing (KIII) modes have been investigated. Also, variations of the KII and KIII values versus wheel rolling angles and frictions have been considered. The validity and accuracy of the cracked model created by sub‐modeling technique have been verified by half‐space modeling and weight function method.

Rupture-induced dynamic pore pressure effect on rupture

The ordinary elasticity model is often used in dynamic rupture earthquake simulation without incorporating the poroelasticity effect in rocks. In consideration that rocks are porous and saturated, we carry out a two-dimensional simulation of spontaneous rupture in a poroelastic medium with a finite difference time domain scheme. In particular, the influence of the rupture-induced pore pressure on the rupture process is investigated. The fault plane is idealized as an impermeable layer of negligible thickness, and the rupture is assumed to be governed by the slip-weakening friction law. Results show that an impermeable fault plane leads to a rupture-induced pore pressure change, which promotes or hinders the rupture process by altering effective normal compressive stress (normal compressive stress minus pore pressure). It is remarkable that super-shear rupturing will occur when the porosity of the rock around the fault increases to some extent. The comparison with the permeable fault model suggests that the permeability of the fault and the porosity of rocks around the fault significantly influence the dynamic rupture process.

Thermomechanical analysis of foulants and graphene platelets reinforced polymer matrix coated steel substrates

Graphene-polymer nanocomposite coatings are used to improve upon the thermal conductivity of metallic substrates. Here we quantify the enhancement provided by coatings comprised of graphene nano platelets (GNPs) of aspect ratios 1, 1.25, 1.5, 1.75, and 2 and mass fractions 0.1, 0.3, and 0.5 either randomly distributed or aligned in one-direction in an epoxy matrix. We first find thermal conductivities, thermal expansion coefficient and the elastic moduli of the homogenized GNPs/matrix by using results of the 3-dimensional (3-D) deformations of the GNPs/matrix representative volumes analysed by the finite element method (FEM). These values are compared with those determined from the rule of mixtures, the inverse rule of mixtures, and the Halpin-Tsai equations. They are then used to analyse, by the FEM, 2-D uncoupled thermo-mechanical deformations of a stainless-steel plate coated with either a foulant (biofilm, aluminium oxide, magnesium carbonate, and calcium sulphate) or a thin GNPs/epoxy layer. It is found that the biofilm hinders most the heat exchange between the plate and its surroundings and the unidirectional oriented GNPs/epoxy coating the least. For the system studied, the compressive normal stress induced at the perfectly bonded interface between the coating and the steel plate can hinder delamination there.

Effect of neurodynamic mobilization techniques in patients with diabetic neuropathy

Purpose.Neurodynamic mobilization is a set of passive or active movements aimed at restoring the neural system’s ability to bear the normal compressive, friction, and tensile stresses encountered in daily life. This study aimed to investigate the effect of neurodynamic mobilization on sensory and motor nerve conduction studies, pain, and functional activity in patients with type 2 diabetic neuropathy (DN).Methods.A total of 42 patients were randomly assigned to the neurodynamic mobilization group (NMG) or selected therapy program group (STPG). Electrophysiological measurements for median sensory and tibial motor nerve conduction velocity, and functional activity were conducted using the Katz Index of Independence, while pain was evaluated using the visual analogue scale.Results.Improvement was noted in the post-treatment median sensory (<i>p</i> = 0.002) and tibial motor (<i>p</i> < 0.001) nerve conduction velocity, functional activity (<i>p</i> < 0.001), and pain (<i>p</i> < 0.001), and a statistically significant difference was demonstrated for the NMG, but not for the STPG.Conclusions.Neurodynamic mobilization improved the sensory and motor nerve conduction velocity, functional activity, and pain in patients with type 2 DN.