Tensile Stress Distribution Research Articles

The effect of braking energy on the fatigue crack propagation in railway brake discs

Thermal fatigue cracks can often be found on the friction surface of brake discs used in railway vehicles after a period of usage and include crackle, radial and circumferential patterns. These cracks typically exhibit different initiation and propagation behavior under different braking conditions. In this paper, the effect of braking energy on fatigue crack evolution is analyzed by using experimental testing and numerical simulations. Macro observations show that a significant number of radial cracks appear on the surface of brake discs which operate at 300km/h, while crackles typically appear after repeated emergency braking (EB) at 200km/h. No crack growth was observed on disc surfaces after routine braking. The cyclic load that leads to the fatigue crack propagation consists of compressive stress during braking and residual tensile stress after cooling. Simulation results show that the depth of cracks correlates well with the residual tensile stress distribution in brake discs. Breaking tests exposed that the fracture surface of fatigue cracks which were covered by oxides shows nearly elliptic-type. Higher braking energy leads to a hardened layer on the friction surface and oxide generation near the crack edges, which are also important factors that contribute to accelerating crack propagation.

Testing and analysis of viscoelastic characteristics of solidifying concrete pavement slabs

To accurately estimate the tensile stress distribution in concrete pavement slabs, their viscoelastic characteristics must be clearly identified, because in a drying concrete slab, creep and stress relaxation occur in a complex manner over a long time. In this study, a restrained ring test was conducted to determine the viscoelastic characteristics of a concrete pavement slab. Finite Element Analysis (FEA) was performed to simulate the restrained ring test using the solidifying viscoelastic properties obtained from the modified elastic-viscoelastic correspondence principle to verify the effect of the viscoelastic material properties. The tensile stress calculated by the viscoelastic analysis was observed to be ∼50% of that obtained from the elastic analysis. The FEA was performed under assumed environmental conditions for the elastic and viscoelastic models of a concrete pavement. Further, the maximum tensile stress based on the viscoelastic model was observed to be 45–55% less than that based on the elastic model owing to stress relaxation. It is concluded that the model that considers the solidifying viscoelastic properties shows better analysis results for tensile stress distribution in a concrete pavement. With better and more accurate estimates of the concrete pavement responses, a pavement that is more structurally sound can be designed.

Influence of shear stress on vector magnetic properties of non-oriented electrical steel sheets

Electrical steel sheet that is used as a core in electrical machines deteriorates due to residual stress and external stress. The magnetic properties and stress need to be clarified in order to effectively utilize electrical steel sheet in electrical machines. We have measured the residual stress distribution in a motor core using an X-ray stress measurement device and clarified not only the tensile and compressive stress distributions, but also the shear stress distribution. In this study, a new measurement system is developed for determining vector magnetic properties under shear stress. The vector magnetic properties of the non- oriented electrical steel sheets under the alternating magnetic flux and rotating magnetic flux conditions were measured with the developed system. As the result, it was clear that the magnitude of the magnetic field strength vector and the magnetic power loss along the direction of about 135 ◦ increased by applying the shear stress.

Elastic Coating with Inhomogeneous Interlayer Under The Action of Normal and Tangential Forces

We consider a three-dimensional problem of the theory of elasticity for an inhomogeneous half space loaded by normal and tangential forces distributed over a circular domain on its surface. The half space consists of a homogeneous base, a homogeneous layer, and an inhomogeneous interlayer whose Poisson’s ratio is constant and the dependence of its Young’s modulus on the distance to the surface of the base is described by a linear function. We study the influence of the thickness of interlayer on the distribution of tensile stresses in the coating.

Effects of Flange Width Ratio on the Residual Stresses in Welded Monosymmetric I-Section

This paper used ANSYS finite element software to simulate the residual stress of the welded monosymmetric I-section and obtain residual stress distribution curves, analyzed the influence of flange width ratio on welding residual stress peak value and the stress distribution. The studies have shown that: with the flange width ratio decrease gradually, peak value of residual stress in flange and web is to increase; peak value of residual tensile stresses in both flange and web close to the steel yield strength fy, peak value of residual compressive stresses is 0.4fy in wide flange and the web near wide flange and in narrow flange and web near narrow flange is 0.3fy; the distribution of the residual tensile stress in the flange and web have growth trend.

繰り返し荷重下での丸鋼と低強度コンクリート間の付着応力度分布に関する研究

The propose of this investigation was to determine the distribution of bond stress between plain round bars and low strength concrete from cyclic pull-out testing. Considered main parameter was the length of embedment bars in this paper. From the test results, tensile stress and bond stress distribution of the embedded bar were obtained. The location of the peak bond stress shifted from the loaded end toward the unloaded end of the bars with increasing applied load. When tensile load decreased to zero the residual stress was occurred in the bar. In addition, even though the applied load was reversed, bond stress distribution along the bar was still constant.

Differences in anatomy and kinematics in Asian and Caucasian TKA patients: influence on implant positioning and subsequent loading conditions in mobile bearing knees.

The objective of our study was to determine the mechanical stress conditions under tibiofemoral loading with an overlay of knee kinematics in deep flexion on two different mobile bearing designs in comparison to in vivo failure modes. This study investigates the seldom but severe complication of fatigue failure of polyethylene components at mobile bearing total knee arthroplasty designs. Assuming a combination of a floor-based lifestyle and tibial malrotation as a possible reason for a higher failure rate in Asian countries we developed a simplified finite element model considering a tibiofemoral roll-back angle of 22° and the range of rotational motion of a clinically established floating platform design (e.motion FP) at a knee flexion angle of 120° in order to compare our results to failure modes found in retrieved implants. Compared to the failure mode observed in the clinical retrievals the locations of the occurring stress maxima as well as the tensile stress distribution show analogies. From our observations, we conclude that the newly introduced finite element model with an overlay of deep knee flexion (lateral roll-back) and considerable internally rotated tibia implant positioning is an appropriate analysis for knee design optimizations and a suitable method to predict clinical failure modes.

Effect of temperature-induced load on airport concrete pavement behavior

In many countries, airport pavements are designed according to the Federal Aviation Administration (FAA) Rigid and Flexible Iterative Elastic Layer Design (FAARFIELD) program. FAARFIELD is capable of analyzing airport pavement behavior based on both the layered elastic-based and three-dimensional finite-element-based design methods. Although the FAA design methods accommodate the mechanical principles needed to calculate the slab thickness required for a given aircraft fleet mix, the effect of temperature-induced loading on the concrete pavement behavior is not considered. This paper presents the tensile stress distribution of concrete slabs and the landing gear position where the maximum tensile stress is observed when both load-induced and temperature-induced loads are taken into consideration in the analysis. Based on three-dimensional finite element analyses, it was observed that the distress types and locations coincided with the actual distress types and locations that are typically found in the field when both traffic-induced and temperature-induced loadings were considered in the analysis.

Molecular dynamic simulation of oblique pullout of carbon nanotube from resin

In this study, a molecular dynamic model was employed to simulate oblique extraction of a multi-walled carbon nanotube (MWNT) from resin and to calculate the carbon nanotube’s (CNTs) deformation and stress distribution. Numerical results reveal the occurrence of elongation and necking in a CNT prior to the movement of its embedded end and of local buckling in a segment near where a CNT exits resin under large angle oblique extraction. Numerical results for the 0°, 15°, 30°, 45°, 60° and 75° oblique extractions reveal the effects of the oblique angle on the force–displacement curve and the tensile stress distribution over selected CNT cross-sections. Based on the simulation results, it is noted that CNT breakage in large-angle oblique extraction is mainly attributed to stress concentration caused by local buckling and it has a detrimental effect on the CNT toughening capacity.

Residual stress of 460 MPa high strength steel welded i section: Experimental investigation and modeling

A reliable estimation of residual stress within steel sections is important in steel structural design and construction, especially for high strength steel which has been increasingly used in recent years. An experimental investigation was conducted in this paper to quantify the residual stresses in 460 MPa steel welded I sections using sectioning method. The magnitude and distribution of both compressive and tensile residual stresses were obtained based on 1972 sets of original data measured from eight different sections. The effects of width-thickness ratios of the flange and web, steel plate thickness, weld type and interaction of the flange and web were investigated. It was found that the compressive residual stress magnitude was largely related to the sectional dimension, while no direct correlation was found with the weld type and size for tensile ones. No residual stress interaction between the flange and web was identified because of the stress equilibrium within each individual part. In addition, a distribution model was proposed in this paper and well described the experimental results, which can be used to investigate and design the buckling behavior of 460 MPa high strength steel members.

Non-destructive residual stress evaluation in mechanically surface treated Ti–2.5Cu by diffraction techniques

Residual stress evaluation is an important stage to interpret the fatigue behavior of many engineering materials. The present research aimed at evaluating non-destructively the macroscopic compressive and balancing tensile residual stresses generated in the surface layer and in the core region, respectively, in mechanically surface treated alpha titanium alloy Ti–2.5Cu. In order to achieve that purpose, a combination of energy-dispersive X-ray and neutron diffraction was used. Results revealed that the zero-crossing depths (where the residual stress value of zero is reached) and balancing tensile residual stress distributions in the core region were well defined.

Finite Element Analysis of Thermo-Mechanical Properties of 3D Braided Composites

This paper presents a modified finite element model (FEM) to investigate the thermo-mechanical properties of three-dimensional (3D) braided composite. The effective coefficients of thermal expansion (CTE) and the meso-scale mechanical response of 3D braided composites are predicted. The effects of the braiding angle and fiber volume fraction on the effective CTE are evaluated. The results are compared to the experimental data available in the literature to demonstrate the accuracy and reliability of the present method. The tensile stress distributions of the representative volume element (RVE) are also outlined. It is found that the stress of the braiding yarn has a significant increase with temperature rise; on the other hand, the temperature change has an insignificant effect on the stress of the matrix. In addition, a rapid decrease in the tensile strength of 3D braided composites is observed with the increase in temperature. It is revealed that the thermal conditions have a significant effect on the strength of 3D braided composites. The present method provides an effective tool to predict the stresses of 3D braided composites under thermo-mechanical loading.

Stress Distribution Characteristics of Runway Pavement under New Generation Large Aircrafts

New Generation Large Aircrafts became a new member of China large airports. However, its heavy weight and high contact pressure would have great impact on the flexible runway pavement. in this paper, based on the multilayered elastic theory, the tensile stress distribution under different airplane was studied to obtain the critical load positions. Furthermore, parameter sensitivity analysis was conducted, including thickness and modulus of Asphalt Stabilized Base (ATB) layer. Results indicated that increasing ATB thickness can only decrease the tensile stress a little, and increasing the modulus of the ATB layer will be more efficient than increasing its thickness. Finally pavement design suggestions composing of both the structural and material considerations were proposed.

Change of Steel’s Yield Stress Over Ship’s Service Life and its Effect on the First Yield Hull Girder Bending Moment - Technical Note

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship's service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability that the total hull girder bending moment will exceed the first yield bending moment) could be substantial.

Research on Sirospun yarn torque using airflow false twisting device

Yarn torque is one of the most important indexes of yarn quality, which is determined on the mechanical state of the constituent fibers and their configuration in the yarn. The fiber tension within a yarn was proposed to be the most influential factor governing the magnitude of yarn torque by Bennett and Postle. Therefore, the research on Sirospun yarn torque is investigated by analyzing the fiber tension at spinning triangle in this paper. Firstly, theoretical models of the fiber tension distributions at primary and final spinning triangles are presented, and corresponding residual torque within a yarn due to the fiber tension is given. The relationships between the yarn torque and the spinning triangle parameters are analyzed theoretically. Secondly, as an application of the proposed method, a modified Sirospun spinning system with an airflow false twisting device which can change spinning triangle parameters are investigated, and the properties of spun yarns produced by the modified system are evaluated and analyzed. It is shown that with the increasing airflow pressures, the Sirospun yarn shows a more and more uniform distribution of tensile and compressive stress within a yarn, and thus the yarn torque decreases correspondingly.

Effects of pretreatment and HVOF sprayed cermet coating on fatigue properties of TC21 titanium alloy

The effects of grit blasting (GB), shot peening (SP) pretreatment and high velocity oxygen fuel(HVOF) sprayed WC-17Co cermet coating on the fatigue properties of the novel ultra-high strength TC21 titanium alloy were investigated with a rotating bending fatigue test machine. The basic properties and surface integrity of the coating were investigated by using X-ray diffraction (XRD), surface roughness meter, microscopic hardness tester, scanning electron microscopy (SEM) and X-ray stress test instruments. The results showed that the residual compressive stress could be introduced into the surface of TC21 alloy by GB and SP pretreatment, and that HVOF sprayed WC-17Co coating was compactly bonded with TC21 alloy substrate and it significantly improved the surface hardness of the substrate. However, there was a certain residual tensile stress in the sublayer of the coating. SP could significantly increase fatigue resistance of TC21 alloy due to the surface residual compressive stress. There was no significant effect on fatigue resistance by GB treatment due to the offset between the influence of surface residual compressive stress and the surface notch effect. The fatigue resistance of TC21 alloy was significantly reduced by HVOF WC-17Co coating prepared with GB pretreatment. This could be attributed to the relaxation of surface residual compressive stress during the HVOF heating process, pore defects and residual tensile stress distribution in the WC-17Co coating with low toughness, and the surface notch induced by GB. The fatigue resistance of TC21 alloy was slightly reduced by HVOF WC-17Co coating prepared with SP pretreatment. This was attributed to the offset between the advantage effect by SP and disadvantageous effect of WC-17Co coating and high temperature factor during the HVOF process.

Residual stress of 460 MPa high strength steel welded box section: Experimental investigation and modeling

An experimental study is presented to investigate and model the residual stress in 460MPa high strength steel welded box sections using the sectioning method. A total of six square box sections with various width-thickness ratios and thicknesses of steel plates were tested and over 2000 original readings were obtained to quantify the magnitude and distribution of both compressive and tensile residual stresses. The effects of width-thickness ratio and plate thickness on residual stresses, the human error and interaction of the four component plates were clarified. The compressive residual stress magnitude was found to be significantly correlated with the sectional dimensions; while for the tensile stresses near the weld region no clear correlation was found. The human error obtained through the comparison of experimental results measured by two persons for the same section was quite small. No residual stress interaction among four component plates was identified due to the residual stress equilibrium within each plate. Finally, a distribution model and its simplified form were established in this study, and a good agreement was found in the comparison with experimental results.

Effects of tool diameters on the residual stress and distortion induced by milling of thin-walled part

Residual stress has a sustained impact on the deformation of thin-walled parts after processing, raising the strict restrictions required in their using procedure. In general, with regard to thin-walled parts, different processing parameters will affect the distortion and residual stress generation of the workpiece, which play the key role in the machining. However, controlling the material removal rate is also quite critical to machining of thin-walled parts. In order to reach these goals, based on the relation between residual stress and uncut chip thickness (UCT), a method is proposed by optimizing the milling tool diameters. The research finding reveals that, by improving the tool diameter, at the same circular position, smaller UCT can be achieved. In addition, take 6 and 12 mm tool diameter as analysis cases; larger tool diameter can reduce the residual tensile stress distribution significantly (the ratio ranges from 13.9 to 34.7 %) and improve the material removal rate. Moreover, a typical thin-walled part is evaluated using different tool diameters (6 and 12 mm) by experiments, as the final distortion can be decreased by 60 % with 12-mm tool diameter. The distribution of machined surface and subsurface residual stress is turning to be more uniform. Hence, it proves that, under the goals of maintaining machining accuracy and material removal rate, also improving the distribution of residual stress, it is possible to achieve by controlling the UCT (tool diameters) in the processing of thin-walled. All these findings can help to enhance the milling precision of thin-walled parts, as well as control and optimize the residual stress distribution.

Effect of Pulsed Current on Temperature Distribution and Characteristics of GTA Welded Magnesium Alloy

This paper compares temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded AZ31B magnesium alloy joints. The effect of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution are reported. The use of pulsed current technique has been found to improve the tensile properties of the welds compared to those of continuous current welds due to grain refinement occurring in the fusion zone.

Semi-analytical solution for electromagnetothermoelastic creep response of functionally graded piezoelectric rotating disk

Time-dependent electromagnetothermoelastic creep response of rotating disk made of functionally graded piezoelectric materials (FGPM) is studied. The disk is placed in a uniform magnetic and a distributed temperature field and is subjected to an induced electric potential and a centrifugal body force. The material thermal, mechanical, magnetic and electric properties are represented by power-law distributions in radial direction. The creep constitutive model is Norton's law in which the creep parameters are also power functions of radius. Using equations of equilibrium, strain-displacement and stress–strain relations in conjunction with the potential-displacement equation a non-homogeneous differential equation containing time-dependent creep strains for displacement is derived. A semi-analytical solution followed by a numerical procedure has been developed to obtain history of stresses, strains, electric potential and creep-strain rates by using Prandtl–Reuss relations. History of electric potential, Radial, circumferential and effective stresses and strains as well as the creep stress rates and effective creep strain rate histories are presented. It has been found that tensile radial stress distribution decreases during the life of the FGPM rotating disk which is associated with major electric potential redistributions which can be used as a sensor for condition monitoring of the FGPM rotating disk.