Shear Stress Amplitude Research Articles

A sectional critical plane model for multiaxial high‐cycle fatigue life prediction

AbstractA stress‐based sectional critical plane model is proposed to predict fatigue life under multiaxial constant amplitude loading. The proposed model considers the effects of material properties and loading paths including stress amplitude ratio, phase angle and mean stress. By introducing the ratio of maximum shear stress amplitude to maximum normal stress amplitude, the crack behaviour can be predicted and the critical planes can be divided into three sections: the maximum normal stress plane, maximum damage plane and maximum shear stress amplitude plane. To verify the accuracy and applicability of the proposed model, experimental data of 30CrMnSiA steel conducted by the authors and other test data of different materials from the existing literatures are utilized. The prediction results demonstrate that the proposed sectional critical plane model shows strong applicability for steel, aluminium and titanium alloy materials, especially under the multiaxial loadings with mean stresses. For steel materials, the prediction results of the proposed model are better than the commonly used criteria.

Cyclic Response of Loose Anisotropically Consolidated Calcareous Sand under Progressive Wave–Induced Elliptical Stress Paths

Observations of the performance of coastal and marine structures in weather events that produce standing and/or progressive waves have pointed to liquefaction of the seabed as a contributing cause of damage. The cyclic response of marine sediments under wave loading can serve to improve the understanding of seabed liquefaction triggering and its consequences. This paper presents the results of an experimental study of the cyclic behavior of loose isotropically and anisotropically consolidated calcareous sand under elliptical stress paths representing progressive waves. Various ratios, λ, of the axial stress difference and torsional shear stress amplitudes were investigated in a hollow-cylinder torsional shear apparatus. The results indicate that the failure mode of isotropically and anisotropically consolidated (IC and AC, respectively) specimens are cyclic mobility and residual deformation failure, respectively. The difference in the observed failure mode appears to be related to particle shape and is independent of λ. However, the cyclic resistance of the calcareous sand is strongly influenced by λ and increases with decreasing consolidation stress ratio, Kc. The cyclic resistance of IC specimens is relatively independent of the orientation of elliptical stress paths, whereas the AC specimens exhibited a marked dependence. The terminal peak excess pore pressure ratio, ru,t, and shear work required for cyclic failure, Wf, are independent of λ; however, ru,t and Wf increases with increasing and decreasing Kc, respectively. Moreover, the relationship between the normalized peak excess pore pressure ratio and normalized shear work is related to the type of soil, but is independent of λ and Kc.

Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material from the bottom up. It has the distinct advantages of low preparation costs and a high geometric creation capability. However, the wide range of industrial processing conditions results in large variations in the fatigue lives of metal components fabricated using AM. One of the main reasons for this variation of fatigue lives is differences in microstructure. Our methodology incorporated a crystal plasticity finite element model (CPFEM) that was able to simulate a stress–strain response based on a set of randomly generated representative volume elements. The main advantage of this approach was that the model determined the elastic constants (C11, C12, and C44), the critical resolved shear stress (g0), and the strain hardening modulus (h0) as a function of microstructure. These coefficients were determined based on the stress–strain relationships derived from the tensile test results. By incorporating the effect of microstructure on the elastic constants (C), the shear stress amplitude (Δτ2) can be computed more accurately. In addition, by considering the effect of microstructure on the critical resolved shear stress (g0) and the strain hardening modulus (h0), the localized dislocation slip and plastic slip per cycle (Δγp2) can be precisely calculated by CPFEM. This study represents a major advance in fatigue research by modeling the crack initiation life of materials fabricated by AM with different microstructures. It is also a tool for designing laser AM processes that can fabricate components that meet the fatigue requirements of specific applications.

Research of flow dynamics and occlusion condition in roller pump systems used for ventricular assist.

Roller pumps have been widely used in the ventricular assist field for many years, while the significant hemolysis caused by its mechanical stress is still a fundamental problem. Although the usual under-occlusion setting was considered as an effective method to reduce the hemolysis rate, its nonocclusive condition of the whole process may cause serious backflow results, which exactly places manyrestrictions on this method. In this study, the simulation experiments based on computational fluid dynamics (CFD) is conducted, and the occlusion angle is proposed and used to explore a more reliable adjustment form of the occlusion condition. The parameterized geometry of a roller pump is established based on the occlusion angle and other parameters. In order to simulate the motion of the roller, the dynamic mesh mode is introduced to the CFD model, and the analytic formulations used to determine the boundary position are derived. In the whole operation process of the roller pump, four feature positions of the rollers were focused and extracted, and the flow characteristics and the shear stress distribution at these positions were demonstrated. It was found that the entry and exit of the rollers could cause clear shear stress peak, especially when one roller entered, the peak got extremely high. Furthermore, the roller pumps with different occlusion angles were compared, and the results showed that decreasing the occlusion angle could lead to a notable decrease in the amplitude and range of high shear stress and the hemolysis index with a small loss of the occlusion duration. It can be concluded that appropriately decreasing the occlusion angle may be an effective method to alleviate the hemolysis which should be given more attention.

Influence of undulating wall heat and mass flux on MHD natural convection boundary layer flow from a vertical wall

AbstractCurrent study expounds an unsteady magnetohydrodynamic natural convective flow along a vertical wall in presence of variable transverse magnetic field. Small amplitude undulation in wall heat flux and wall mass flux are imposed at the vertical wall to generate the boundary layer flow. The flow governing equations are divided into sets of steady and unsteady equations and then transformed into the similarity and nonsimilarity equations, respectively, by introducing stream function formulations. The sets of nonsimilarity equations are solved numerically by using three different techniques, namely, perturbation solution technique, asymptotic solution technique and implicit finite difference technique applied, respectively, for lower, higher, and all frequencies (ξ). Results are illustrated in connection with the amplitude and phase angles of shear stress, wall temperature, and concentration against the frequency (ξ) for wide ranges of physically significant parameters. Likening of the results obtained by above mentioned numerical methods are presented in every figure and table. Results reveal that the amplitude of undulating shear stress and wall temperature dwindle and the amplitude of wall concentration increases due to increment in Prandtl number (Pr). Besides, on incrementing Schmidt number (Sc) the amplitude of undulating shear stress and wall concentration dwindle and the amplitude of wall temperature increases. Results also reveal that on incrementing magnetic parameter (M) the amplitude of transient shear stress dwindles while the amplitude of transient wall temperature and concentration increase.

A convex hull‐based approach for multiaxial high‐cycle fatigue criteria

AbstractDesign methods against multiaxial high‐cycle fatigue require the formulation of appropriate criteria that differ in the definition of critical measures introduced to quantify damage, as the amplitude of shear stress. The present paper proposes a novel approach to compute the amplitude of shear stress in multiaxial high‐cycle fatigue. The approach is based on the computation of the convex hull enclosing the stress history under investigation and is validated on proportional and non‐proportional paths in several dimensions and for different materials. High accuracy is achieved when compared with alternative methods from the literature.

Frictional behavior of sandstone fractures under forward-backward pre-peak cyclic loading

The objective of this study is to determine the effect of cyclic loading under pre-peak condition on shearing behavior of fractures in Phra Wihan sandstone, primarily to improve an understanding of the stability conditions of slope embankments along roadways and railways in the north of Thailand where seismic activities have often occurred. The fractures were artificially made in the laboratory by tension inducing method and cyclically sheared under forward to fully backward loading paths with constant normal stresses between 1 and 4 MPa. Two cyclic loading conditions were used on separate sets of specimens: constant stress amplitude and constant displacement amplitude. Fifty shear cycles were applied. The results indicated that the pre-peak cyclic loading under both loading conditions slightly reduce shear strengths and stiffness of the sandstone fractures due to the degradation of the second order fracture asperities. Fracture roughness notably reduced particularly under large shear stress and displacement amplitudes due to the deposition and packing of rock power. The subsequent monotonic loading performed after cyclic loading showed further reduction of fracture roughness due to the degradations of the first order asperities.

Fatigue performance of profiled steel sheeting–concrete bridge decks subjected to vehicular loads

Bridge decks are usually formed from profiled steel–concrete composite slabs, which consist of steel and concrete. Slip occurs at the interface between the concrete and steel, which results in unique mechanical and fatigue properties of the composite slab. The objective of this study is to investigate the mechanical and fatigue performance of profiled steel sheeting–concrete bridge decks subjected to vehicular loads. A new method for calculating the deflection of profiled steel sheeting–concrete composite slabs based on a discontinuous stiffness is proposed, and the deformation and internal force components of composite plates are deduced theoretically. The midspan deflection and end-slip calculated via this method are close to the experimental values. With a focus on the fatigue performance of the bridge deck, this paper discusses the fatigue design method of the composite slab and presents fatigue-check calculations for the Khartoum Al-Halfaia bridge over the Nile. A parameter analysis of the composite slab bridge was performed. The effects of the thickness and section geometry of the profiled steel plate and the strength grade and thickness of the concrete on the fatigue performance were investigated, and corresponding improvement measures were examined. It was found that the thickness and geometry of the section significantly affect the shear-stress amplitude of the plate end interface, while the concrete strength grade has little influence on the fatigue performance of the composite slab.

Dependence of fatigue limit on stress ratio and influence of cyclic stress on shear strength for an adhesive lap joint

ABSTRACT The improvement in adhesion technology for joining different types of materials has led to expectations of weight reduction in cars and commercial vehicles. Various levels of stress and stress ratios are loaded onto the joints of such transport vehicles. Therefore, the fatigue shear strength of an adhesive lap joint is important. This study is related to the fatigue properties of structural adhesive joints. Lap-joint specimens using epoxy adhesive were prepared, and fatigue tests with four different stress ratios were conducted. Subsequently, the fatigue limit diagram was plotted, and the effect of stress ratio on the fatigue limit was investigated. Moreover, the strength of the specimens subjected to various cyclic stress levels was investigated systemically. With cyclic shear stress, the influence of the shear stress amplitude on the resistance to fatigue failure was more significant than that of the number of cycles. The specimens that endured the fatigue tests maintained approximately the same shear strength as that of the as-received specimens. The findings of this study can provide important guidance for the design of a car body.

Prediction of fatigue damage region with the use of the notch critical plane approach for crack initiation and propagation

The advanced volumetric approaches are reviewed briefly to state the stress/strain-based or energy-based parameters of fatigue damage region are critical. A new approach is proposed to distinguish crack initiation and propagation stage. The angles of crack initiation are predicted by notch critical plane (NCP) approach (Luo et al. Fatigue Fract Eng Mater Struct, 2019, 42(4): 854–870). NCP is the plane which passes through the fatigue critical point (FCP) and undergoes the maximum shear stress amplitude. The experiment of thin-walled round tube components is conducted to check these approaches. The direction of crack initiation is basically the same as that of NCP. Most of the predicted lives fall within an error factor of 3.

High shear stress amplitude in combination with prolonged stimulus duration determine induction of osteoclast formation by hematopoietic progenitor cells

To date, it is unclear how fluid dynamics stimulate mechanosensory cells to induce an osteoprotective or osteodestructive response. We investigated how murine hematopoietic progenitor cells respond to 2 minutes of dynamic fluid flow stimulation with a precisely controlled sequence of fluid shear stresses. The response was quantified by measuring extracellular adenosine triphosphate (ATP), immunocytochemistry of Piezo1, and sarcoplasmic/endoplasmic Ca2+ reticulum ATPase 2 (SERCA2), and by the ability of soluble factors produced by mechanically stimulated cells to modulate osteoclast differentiation. We rejected our initial hypothesis that peak wall shear stress rate determines the response of hematopoietic progenitor cells to dynamic fluid shear stress, as it had only a minor correlation with the abovementioned parameters. Low stimulus amplitudes corresponded to activation of Piezo1, SERCA2, low concentrations of extracellular ATP, and inhibition of osteoclastogenesis and resorption area, while high amplitudes generally corresponded to osteodestructive responses. At a given amplitude (3 Pa) and waveform (square), the duration of individual stimuli (duty cycle) showed a strong correlation with the release of ATP and osteoclast number and resorption area. Collectively, our data suggest that hematopoietic progenitor cells respond in a viscoelastic manner to loading, since a combination of high shear stress amplitude and prolonged duty cycle is needed to trigger an osteodestructive response. PLAIN LANGUAGE SUMMARY: In case of painful joints or missing teeth, the current intervention is to replace them with an implant to keep a high-quality lifestyle. When exercising or chewing, the cells in the bone around the implant experience mechanical loading. This loading generally supports bone formation to strengthen the bone and prevent breaking, but can also stimulate bone loss when the mechanical loading becomes too high around orthopedic and dental implants. We still do not fully understand how cells in the bone can distinguish between mechanical loading that strengthens or weakens the bone. We cultured cells derived from the bone marrow in the laboratory to test whether the bone loss response depends on (i) how fast a mechanical load is applied (rate), (ii) how intense the mechanical load is (amplitude), or (iii) how long each individual loading stimulus is applied (duration). We mimicked mechanical loading as it occurs in the body, by applying very precisely controlled flow of fluid over the cells. We found that a mechanosensitive receptor Piezo1 was activated by a low amplitude stimulus, which usually strengthens the bone. The potential inhibitor of Piezo1, namely SERCA2, was only activated by a low amplitude stimulus. This happened regardless of the rate of application. At a constant high amplitude, a longer duration of the stimulus enhanced the bone-weakening response. Based on these results we deduce that a high loading amplitude tends to be bone weakening, and the longer this high amplitude persists, the worse it is for the bone.

Shear cracks of Zircaloy tube during cold pilgering: experimental investigation and numerical modeling

Cold pilgering process is a seamless tube forming technology, in which the metal is subjected to a series of small incremental deformations. It has been extensively applied for the manufacturing of cladding tube in nuclear reactors, due to high dimensional accuracy and favorable texture evolution. Notwithstanding, the pilgered tubes showed a kind of shear cracks similar to those obtained during low-cycle shear fatigue experiments. To confirm it, a novel low-cycle shear fatigue experiment was designed, in which the shear stress amplitude was obtained from a tracking point in the inner surface of the pilgered tube through finite element model (FEM). Additionally, a theoretical model was established based on the experimental results to predict fatigue life during the cold pilgering process. Through this model, the effects of Q value, side relief, and friction coefficient on the safety factor during cold pilgering were investigated. The results showed that with the increase of Q value, and the decrease of the difference between the friction coefficients of the inner and outer surfaces, the safety of cold pilgering tube could be improved by decreasing the tendency of shear cracks.

Reliability on ProSHAKE 2.0 in the Assessment of One Dimensional Ground Response Analysis through Verification Example

It is understood from the recent destructive earthquakes, topography, nature of the bedrock and geometry of the soil deposits are the prime factors that made modifications to the underlying earthquake motion. The influence of such confined soil states on the strong earthquake motion plays a significant task in accessing the uniqueness of ground action. In this paper, the response of the soil layers to the earthquake action of the bedrock directly under it is determined. The analysis is done through frequency domain approach. Pro-shake software 2.0 is used to arrive the reliability of the ground response study. A wide variety of output parameters such as time histories of acceleration, velocity, displacement, shear stress, shear strain, response spectra and maximum amplitude of various parameters with depth are plotted and the other scalar parameters such as peak acceleration, peak velocity, peak displacement, RMS acceleration, arias intensity, predominant period and bracketed duration was computed.

Fast estimation of the shear stress amplitude for fatigue life analysis of metals

The aim of this paper is to propose a numerical approach for computing the shear stress amplitude during one loading cycle. The analysis is based on the material history in the space of the deviator. It is shown that the calculated maximal amplitude can be used as a satisfactory upper estimate of the amplitude obtained with critical plane theories. The main benefit of this approach is its very low CPU time consuming compared to the algorithms used in the literature. By this way, the proposed approach allows analyzing a high number of material points in the case of the FEM analysis of a structure or a high number of temporal points in the case of an experimental high frequency measurement. Examples are presented to show the relevance and the efficiency of the numerical algorithm proposed.

Heart rate effects on the ventricular hemodynamics and mitral valve kinematics

This paper aims at studying the effects of the heart rate (HR) on the intraventricular hemodynamics and mitral valve dynamics for a healthy left ventricle of the human heart. The problem is tackled through direct numerical simulation of the Navier-Stokes equations, two–way coupled with a structural solver for the ventricle and mitral valve leaflets. Several HRs ranging from bradycardia to normal and up to tachycardia are considered and the resulting flow and structure dynamics analysed.Taking the physiological HR of 60 beats per minute (bpm) as reference case, it results that in the bradycardia regime the lower flow rates produce a weaker mitral jet with a lower blood kinetic energy and smaller wall shear stresses either on the valve leaflets and on the endocardium. In contrast, as the HR increases, the faster and thicker mitral jets are associated to increasing blood kinetic energy and the wall shear stress, which more than double increasing the HR from bradycardia to tachycardia. The altered wall shear stress distribution and amplitude, though not intense enough to produce immediate effects, are implied to induce, in the long-term, structure alteration or tissue remodelling via mechanotransduction mechanisms [1]. Another relevant effect of the HR increase is the reduction of the diastasis duration until at HR=100 bpm the early diastole (E–wave) overlaps the late diastole (A–wave). This phenomenon produces an enhanced mitral leaflets mobility, which open more at higher HRs, thus yielding larger geometrical orifice area during diastole.

Resilient behavior of coarse granular materials in three-dimensional stress state

The traffic-induced cyclic stresses on the road base and subbase courses are usually in three-dimensional stress state, while so far most laboratory studies have focused on the deformation behavior of base and subbase layers in axisymmetric stress state. This study investigates the three-dimensional resilient behavior of coarse granular base and subbase materials based on a true triaxial apparatus. The factors of effective confining pressure, [Formula: see text], amplitude of cyclic shear stress, qampl, coefficient of cyclic intermediate principal stress, bcyc, and fines content are involved. Test results indicate that the increase of either [Formula: see text] or qamplleads to a nonlinear growth of resilient modulus with a decreasing growth rate. bcyc, which is proposed to represent the coupling of cyclic major and intermediate principal stresses, is found to have a promotion effect on the resilient stiffness, and the promotion effect tends to be enhanced by the increase of qampl. A modified model is established to predict the resilient modulus of coarse granular materials in three-dimensional stress state. There appears to exist a critical value of fines content, at which the variation trend of resilient modulus is changed from increasing to decreasing, and the critical fines content is related to both [Formula: see text] and bcyc.

Influence of strain histories on liquefaction resistance of sand

The liquefaction resistance of sand increases with cyclic pre-shearing and pre-shaking as a result of earthquakes if the strain level in the pre-shearing is small. When larger shear strains are imposed, liquefaction resistance decreases. These complicated effects of pre-shearing histories on the liquefaction resistance are investigated in this study through a series of cyclic triaxial tests. Various combinations of cyclic stress amplitude and number of cycles of pre-shearing are examined. The tested sand is Toyoura Sand at 45% relative density, under a confining pressure of 50 kPa. Test results indicate that for the range of shear strain amplitude in pre-shearing smaller than 0.35%, the liquefaction resistance increases with pre-shearing. The increase in the liquefaction resistance depends strongly on the volumetric strain in the pre-shearing, and several effects of the shear stress amplitude and number of cycles can be negligible. Small volumetric strain of the order of 1% doubled the liquefaction resistance. Meanwhile, in the range of shear strain amplitude larger than 0.6%, the liquefaction resistance decreases. The liquefaction resistance decreases as the shear strain amplitude increases. Shear strain amplitude is one of the factors dominating this degrading effect, and the volumetric strain exerts beneficial effects to a certain extent. In this study, another series of tests are conducted to investigate the combined effects of small and large strain amplitude pre-shearing. It is observed that small shear strain pre-shearing cycles subsequent to large shear strain cycles erased the degrading effect of the latter. However, a large shear strain pre-shearing after small strain cycles degrades the beneficial effect of the small shear strain pre-shearing cycles previously applied to the specimens; however, the effects of the former small strain pre-shearing remains.

Hybrid mediated blood flow investigation for atherosclerotic bifurcated lesions with slip, convective and compliant wall impacts

ObjectiveThe present investigation is concerned with hybrid mediated blood flow model through atherosclerotic bifurcated artery with slip effects by considering the properties of compliant walls. Design/approachIn human body, the circulatory system is made up of a network of blood vessels that include the bifurcation therefore the influence of hybrid nanoparticles on parent artery with mild stenosis, at apex and in the region of daughter arteries (after being bifurcated) is observed. Blood streaming along the segment of vessel is considered to be Newtonian. The compliant nature of the atherosclerotic artery wall is also considered to create association with permeability aspects for the thickness of arterial wall. Property of heat transfer with convective impacts is taken into account to weaken the stenotic lesions. Through phase flow model approach, a mathematical model is develop with the phenomena of hybrid nanofluid. FindingsFor theoretical research of designed equations experimentally determined values of nanoparticles and base fluid are used. Further, flow configurations of hemodynamics are figure out to analyze the blood flow through bifurcated stenotic artery. The comparison in parent and daughter artery is plotted for velocity profile. These patterns provide us a graphical way to recognize the importance of theoretical assistance of this model to biomedical field. At the end, it is concluded from graphical results that slip to the boundary reduces the resistance to flow for atherosclerotic bifurcated artery. ConclusionsIn bifurcated artery, blood circulation is assumed due to difference of pressure between atherosclerotic and non-atherosclerotic portions. Slip impacts are more effective to reduce the hemodynamics effects of stenosis for bifurcated artery. Bifurcation angle reduces the shear stress for daughter artery whereas opposite behavior is observed for parent artery. Compliant wall parameters reduces the inner bolus size in stenotic region while number of bolus increases in bifurcated region. Reduction in the amplitude of shear stress for convective parameter is more prominent in the parent artery as compared to daughter artery.

Multiaxial fatigue of quenched and tempered U2 steel: Testing and fatigue life prediction

AbstractTension‐compression, tension‐tension, torsional, and 90° out‐of‐phase axial‐torsional fatigue tests were performed on a quenched and tempered U2 steel. All tests were conducted under force/torque control because macroscopic plastic strains were insignificant in the life range of interest (from 104 to 2 × 106 loading cycles). Stress‐based versions of the Fatemi‐Socie critical plane parameter and of the Smith‐Watson‐Topper parameter with a critical plane interpretation were evaluated using the experimental data. The Smith‐Watson‐Topper parameter was not able to correlate the test data. The Fatemi‐Socie method correlated most of the test data within factor‐of‐three boundaries. A modified Crossland invariant‐based parameter made of two interaction rules between the shear stress amplitude and the maximum hydrostatic stress, and of a definition of shear stress amplitude based on the maximum prismatic hull method, yielded fatigue life estimates in reasonable agreement with the experimental observations.

Study on dynamic stress-strain response law of frozen saline soil

The subgrade saline soil in a certain area of western Qinghai province was studied, based on the British GDS dynamic triaxial test system, the dynamic triaxial test under laboratory test was carried out to study variation dynamic stress-strain and dynamic shear modulus under the different temperature, frequency and confining pressure. The test results show that the dynamic stress-strain relationship is significantly affected by temperature change under cyclic dynamic load, followed by frequency and confining pressure. Under the same strain amplitude, the lower the temperature, the larger the dynamic shear modulus. When frequency and confining pressure increase, dynamic shear modulus also increases. Whereas, the influence of confining pressure on the dynamic shear modulus is more obvious, and the backbone curve development trend is steeper. Both maximum dynamic shear modulus and final shear stress amplitude increase with the frequency increases when temperature and confining pressure remain unchanged. Meantime, the maximum dynamic shear modulus curve is a convex shape, and the final shear stress amplitude curve is a convex shape at positive temperature,while which a concave shape at negative temperature. At constant frequency and confining pressure, the maximum dynamic shear modulus and final shear stress amplitude increase with the decrease of temperature. Curves of change trend are slower above 0°C, and steeper below 0°C.