Stress Loading History Research Articles

Influence of Fault System Geometry and Slip Rates on the Relative Role of Coseismic and Interseismic Stresses on Earthquake Triggering and Recurrence Variability

AbstractWe model Coulomb stress transfer (CST) due to 30 strong earthquakes occurring on normal faults since 1509 CE in Calabria, Italy, including the influence of interseismic loading, and compare the results to existing studies of stress interaction from the Central and Southern Apennines, Italy. The three normal fault systems have different geometries and long‐term slip‐rates. We investigate the extent to which stress transfer can influence the occurrence of future earthquakes and what factors may govern the variability in earthquake recurrence in different fault systems. The Calabrian, Central Apennines, and Southern Apennines fault systems have 91%, 73%, and 70% of faults with mean positive cumulative CST in the time considered; this is due to fewer faults across strike, more across strike stress reductions, and greater along‐strike spacing in the three regions respectively. In regions with close along strike spacing or few faults across strike, such as Calabria and Southern Apennines, the stress loading history is mostly dominated by interseismic loading and most faults are positively stressed before an earthquake occur on them (96% of all faults that ruptured in Calabria; 94% of faults in Southern Apennines), and some of the strongest earthquakes occur on faults with the highest mean cumulative stress of all faults prior to the earthquake. In the Central Apennines, where across strike interactions are the predominant process, 79% of earthquakes occur on faults positively stressed. The results highlight that fault system geometry plays a central role in characterizing the stress evolution associated with earthquake recurrence.

Investigation of fatigue damage of new-old concrete interface based on piezomagnetic effect

Prefabricated concrete structures that employ wet connections create a new-old concrete interface between the pre-cast and cast-in-place layers. To enhance interfacial bonding performance in practical engineering, steel shear keys are frequently employed. The performance of the new-old concrete interface is critical in determining the fatigue performance of prefabricated concrete structures. Therefore, detecting and monitoring interface fatigue damage is essential for the life prediction and damage assessment of the entire structure. This study measured and analysed the piezomagnetic signal of the new-old concrete interface with shear keys under both static and cyclic loads. The piezomagnetic induction intensity was studied based on multiple damage indicators, such as steel strain and interface deformation. The relationship between the piezomagnetic signal and interface fatigue damage was analysed. The magneto-mechanical effect, dislocation effect, and magnetic leakage effect govern the piezomagnetic field change in different fatigue stages. It is found that the piezomagnetic signal exhibits similarities with conventional fatigue damage indicators, undergoing a three-stage variation pattern. Moreover, it demonstrates greater sensitivity to stress loading history and can better reflect the evolution of microstructural defects within the material. Finally, a simulated model of the magnetisation of the shear key at the new-old concrete interface was established and validated.

Establishment of sheet metal forming wrinkling limit diagram (WLD) and research on the consistency of WLDs in different processes

With the actual demand for lightweight and high strength of metal parts, wrinkling has become one of the main problems restricting the overall forming of thin-wall members. Therefore, the efficient and accurate prediction and control of it have actual significance. In this work, a critical principal strain analytic model for plate and shell wrinkling was set up with the combination of energy method theory and plastic flow law of material. And a numerical procedure of establishing the wrinkling limit diagram (WLD) was developed based on the finite element method and the critical principal strain analytic model. With the sidewall wrinkling in deep drawing process of the conical cup and the wrinkling of square plate in the Yoshida bucking test (YBT) as the analysis object, the morphology and the characteristics of the WLD under different forming processes were studied, and the effect of loading conditions and stress loading history on the WLD was investigated, it is observed that the WLD is different under the same sheet material but different loading conditions, and indicated the WLD is dependent on the loading conditions.

The Ultrasonic P‐Wave Velocity‐Stress Relationship and Energy Evolution of Sandstone under Uniaxial Loading‐Unloading Conditions

As shallow resources are exhausted, deep resources are gradually being exploited; consequently, mining disasters and accidents have increased significantly over time. During mining, a deep rock mass experiences complex mining‐induced stress evolution, damage accumulation, and deformation failure processes, and the mechanical and acoustic properties of the rock constantly change. To better understand the variation in the mechanical and acoustic properties of rock under loading and unloading conditions, uniaxial loading‐unloading experiments with real‐time ultrasonic P‐wave velocity monitoring were conducted on sandstone specimens drilled from a coal seam roof. The test results show that the axial stress level is directly related to the P‐wave velocity. A logarithmic relationship exists between the ultrasonic P‐wave velocity and stress in the tested sandstones. The wave velocity increase caused by the unit axial pressure increase is significantly lower than that at the initial loading stage after entering the higher stress level. The energy evolution of sandstone during loading and unloading is closely related to the stress loading history and reflects the damage accumulation in the rock. Under elastic loading, the energy accumulation is mainly reflected by an increase in elastic energy, and less energy is dissipated during the elastic loading period. Stress unloading causes high energy dissipation, resulting in irreversible strain and damage accumulation, which provides a good basis for using ultrasonic testing to preliminarily judge the failure of a specific rock and formulate corresponding engineering measures.

Stress loading history of earthquake faults influenced by fault/shear zone geometry and Coulomb pre-stress

Whether the stress-loading of faults to failure in earthquakes appears to be random or to an extent explainable, given constraints on fault/shear-zone interaction and the build-up and release of stress over many earthquake cycles, is a key question for seismic hazard assessment. Here we investigate earthquake recurrence for a system of 25 active normal faults arranged predominantly along strike from each other, allowing us to isolate the effects of stress-loading due to regional strain versus across- and along-strike fault interaction. We calculate stress changes over 6 centuries due to interseismic loading and 25 > Mw 5.5 earthquakes. Where only one fault exists across strike, stress-loading is dominated by the regional tectonics through slip on underlying shear zones and fault planes have spatially smooth stress with predominantly time-dependent stress increase. Conversely, where faults are stress-loaded by across-strike fault interactions, fault planes have more irregular stress patterns and interaction-influenced stress loading histories. Stress-loading to failure in earthquakes is not the same for all faults and is dependent on the geometry of the fault/shear-zone system.

Analytical Prediction of Residual Stress in the Machined Surface during Milling

An analytical prediction model for residual stress during milling is established, which considers the thermal-mechanical coupling effect. Considering the effects of thermal-mechanical coupling, the residual stress distribution in the workpiece is determined by the stress loading history according to McDowell′s hybrid algorithm. Based on the analysis of the geometric relationship of orthogonal cutting, the prediction model for milling force and residual stress in the machined surface is established. The research results can provide theoretical basis for stress control during milling.

Fatigue lifetime estimation of bearing pin of console manipulator loaded with multiaxial random loading

Fatigue lifetime estimation of load bearing parts of construction is a key factor in a design of technique used for long term operation. Complex loading in combination with complex geometry of the most loaded parts represents only one of many problems that engineers have to deal with. One of the most commonly used approaches how to deal with this problem is to use the technical standards. This approach, despite its indisputable advantages (clear and comprehensible steps of calculation), has several significant shortcomings (non-economical oversized design). In this paper we propose procedure of how to estimate fatigue lifetime of construction parts that are loaded with random operational loading. The result of proposed procedure is distribution function of fatigue lifetime which takes into account the complex geometry of the designed part and random character of the complex loading (multiaxial stress state) in a hotspot. This approach is then demonstrated on fatigue lifetime estimation of bearing pin of a console manipulator loaded by random operational loading. Loading process was obtained using set of strain gages. The measured loading process was then transformed into stress histories in critical hotspot using FEM. Method of processing the stress loading histories in critical hotspot into a form usable in combination with hypotheses for fatigue damage calculation under multiaxial stress states is presented.

Effect of Hypertension on the Closing Dynamics and Lagrangian Blood Damage Index Measure of the B-Datum Regurgitant Jet in a Bileaflet Mechanical Heart Valve

We hypothesize that the formation of the closing vortex and subsequent b-datum regurgitation jet in bileaflet mechanical heart valves is governed by the magnitude of the driving mean aortic pressure (MAP), and that this sensitivity does impact the blood damage index (BDI) corresponding to platelet activation and lysis. High spatial resolution time resolved (1 kHz) as well as phase locked particle image velocimetry techniques captured the dynamic leaflet closure and regurgitation jet of a model 25 mm St. Jude Medical BMHV. Cell trajectories were estimated using Lagrangian particle tracking analysis while the leaflet kinematics was quantified by tracking the leaflet tip-position throughout closure. The non-principal as well as principal shear stress loading histories along each cell trajectory revealed BDI for platelet activation and lysis as a function of cell initial position, release time-point, and blood pressure. Results show that the leaflet closing time reduces by roughly 10 ms, in response to an increase in MAP by 40 mmHg. We report that higher MAP leads to a stronger b-datum vortex and jet formation. Platelet activation BDI lowers with a higher MAP due to reduction in exposure times despite an increase in principal shear stress experienced. Platelet lysis BDI however increases with higher MAP. Maximum BDI may occur for cells initially in the b-datum zone during the onset of leaflet closure. Our results provide a better understanding of BDI of the regurgitant b-datum jet and sheds light on the potential importance of blood damage testing under hypertensive conditions.

Evaluation of shear stress accumulation on blood components in normal and dysfunctional bileaflet mechanical heart valves using smoothed particle hydrodynamics

Evaluating shear induced hemodynamic complications is one of the major concerns in design of the mechanical heart valves (MHVs). The monitoring of these events relies on both numerical simulations and experimental measurements. Currently, numerical approaches are mainly based on a combined Eulerian–Lagrangian approach. A more straightforward evaluation can be based on the Lagrangian analysis of the whole blood. As a consequence, Lagrangian meshfree methods are more adapted to such evaluation. In this study, smoothed particle hydrodynamics (SPH), a fully meshfree particle method originated to simulate compressible astrophysical flows, is applied to study the flow through a normal and a dysfunctional bileaflet mechanical heart valves (BMHVs). The SPH results are compared with the reference data. The accumulation of shear stress patterns on blood components illustrates the important role played by non-physiological flow patterns and mainly vortical structures in this issue. The statistical distribution of particles with respect to shear stress loading history provides important information regarding the relative number of blood components that can be damaged. This can be used as a measure of the response of blood components to the presence of the valve implant or any implantable medical device. This work presents the first attempt to simulate pulsatile flow through BMHVs using SPH method.

Device Thrombogenicity Emulator (DTE) − Design optimization methodology for cardiovascular devices: A study in two bileaflet MHV designs

Patients who receive prosthetic heart valve (PHV) implants require mandatory anticoagulation medication after implantation due to the thrombogenic potential of the valve. Optimization of PHV designs may facilitate reduction of flow-induced thrombogenicity and reduce or eliminate the need for post-implant anticoagulants. We present a methodology entitled Device Thrombogenicty Emulator (DTE) for optimizing the thrombo-resistance performance of PHV by combining numerical and experimental approaches. Two bileaflet mechanical heart valves (MHV) designs, St. Jude Medical (SJM) and ATS, were investigated by studying the effect of distinct flow phases on platelet activation. Transient turbulent and direct numerical simulations (DNS) were conducted, and stress loading histories experienced by the platelets were calculated along flow trajectories. The numerical simulations indicated distinct design dependent differences between the two valves. The stress loading waveforms extracted from the numerical simulations were programmed into a hemodynamic shearing device (HSD), emulating the flow conditions past the valves in distinct ‘hot-spot’ flow regions that are implicated in MHV thrombogenicity. The resultant platelet activity was measured with a modified prothrombinase assay, and was found to be significantly higher in the SJM valve, mostly during the regurgitation phase. The experimental results were in excellent agreement with the calculated platelet activation potential. This establishes the utility of the DTE methodology for serving as a test bed for evaluating design modifications for achieving better thrombogenic performance for such devices.

Structural integrity analysis of the main bearing cap screws of the turbo-diesel engine crank shaft

This article presents a study about the structural integrity of screws used in the fixation of the main bearing cap of the crank shaft of a turbo-diesel engine. Such a component was chosen for such an analysis for being an element of essential importance in the structural integrity of the engine. In this context, the main failure mode was fatigue. Functions of capacity and demand were determined. Two demand functions were built, one based on Goodman’s diagram and the other one on Gerber’s diagram. The parameters that characterize such functions were obtained by means of tension tests, hardness tests, and finite element analysis. For the characterization of the stress loading history applied in the screw, extensometer techniques were used. Based on those results, safety factor, reliability index and reliability of the screw were considered. The reliability index and the reliability were estimated according to Monte-Carlo, FOSM and ASM techniques. As result it was verified that those values are order 1.66% and 99.9%, respectively, to the safety factor and the reliability.

04/00409 Analysis of noise occurrence by cavitation in the main bearing of diesel engine: Aovama. T. et al. JSAE Review, 2003, 24, (1), 59–64

This article presents a study about the structural integrity of screws used in the fixation of the main bearing cap of the crank shaft of a turbo-diesel engine. Such a component was chosen for such an analysis for being an element of essential importance in the structural integrity of the engine. In this context, the main failure mode was fatigue. Functions of capacity and demand were determined. Two demand functions were built, one based on Goodman’s diagram and the other one on Gerber’s diagram. The parameters that characterize such functions were obtained by means of tension tests, hardness tests, and finite element analysis. For the characterization of the stress loading history applied in the screw, extensometer techniques were used. Based on those results, safety factor, reliability index and reliability of the screw were considered. The reliability index and the reliability were estimated according to Monte-Carlo, FOSM and ASM techniques. As result it was verified that those values are order 1.66% and 99.9%, respectively, to the safety factor and the reliability.

Effect of NOx environments and stress on degradation of mechanical properties of Kevlar 49 and nylon 6

AbstractMechanical and chemical mechanisms may act synergistically to degrade the mechanical properties of polymers. This synergism should be considered during design of components for sustained loads in hostile environments. If these polymers are to be used as load‐bearing structural elements in automobile and industrial environments, they are likely to be simultaneously exposed to such environments and stress. These studies explore the deleterious effects of gaseous pollutants (e.g. NOx in air) and mechanical stress on polymers. This research included studies on nylon‐6 and composites of nylon‐6 yarns embedded in a bis‐A‐phenolic resin with an amine curing agent, as well as single fibers and yarns of poly(p‐phenylene terephthalamide) (DuPont Kevlar 49) as bare fibers and also embedded in an epoxy matrix. The protective effect of embedding fibers in the epoxy matrix was demonstrated. NOx concentrations were varied between 0 and 1.5%. The sustained loads during exposure were in the range of 50 to 80 percent of the ultimate stress short term load carrying capability of the fibers. Exposure times varied from several minutes to months. Electron spin resonance spectroscopy (ESR) is used in these studies to explore the kinetics of bond rupture and how they relate to the environmental and stress loading histories in nylon. Kevlar 49 degradation studies were conducted by measuring times required for sample failure in NOx concentrations at various stress levels. Preliminary studies on the single fibers indicate a stress‐NOx synergism over the range of stresses (48 and 77% of ultimate) and 0.1 and 1.5% gas concentrations. Yarn samples exhibited this synergism over a wide range of stresses (40 to 80% of ultimate). Bare yarn degradation was accelerated by NOx concentrations in air as low as 0.1%. We view these effects as having practical technological significance since these lower NOx concentrations approach the level of emissions from exhaust from older model automobiles.

Thermoviscoplastic analysis of fibrous periodic composites by the use of triangular subvolumes

The non-linear viscoplastic behavior of fibrous periodic composites is analyzed by discretizing the unit cell into triangular subvolumes. A set of these subvolumes can be configured by the analyst to construct a representation for the unit cell of a periodic composite. In each step of the loading history the total strain increment at any point is governed by an integral equation which applies to the entire composite. A Fourier series approximation allows the incremental stresses and strains to be determined within a unit cell of the periodic lattice. The non-linearity arising from the viscoplastic behavior of the constituent materials comprising the composite is treated as a fictitious body force in the governing integral equation. Specific numerical examples showing the stress distributions in the unit cell of a fibrous tungsten/copper metal-matrix composite under viscoplastic loading conditions are given. The stress distribution resulting in the unit cell when the composite material is subjected to an overall transverse stress loading history perpendicular to the fibers is found to be highly heterogeneous, and typical homogenization techniques based on treating the stress and strain distributions within the constituent phases as homogeneous result in large errors under inelastic loading conditions.

An anisotropic creep damage model for multiaxial cyclic loading histories

The purpose of this study is the development of an anisotropic creep damage theory within the continuum damage mechanics, applicable to creep-dominated cyclic loading histories. A damage distribution is expressd in rate form as a symmetric tensor of rank necessary to match physically measured damage. A theoretical model which expresses general anisotropic creep damage phenomena with power law cavity growth is proposed. The coupling of damage with a bounding surface cyclic viscoplasticity theory is also accomplished. Comparison with experimental results are made for weakly anisotropically damaging materials, type 304 stainless steel at 593°C. Good correlation of rupture time, secondary creep, and tertiary creep has been obtained for proportional and nonproportional, isothermal, constant isochronous nominal stress loading histories. A modification of the isochronous stress (the set of stress state which have a same rupture time) for compressive hydrostatic stress state has been offered.

Pore-Pressure Rise Mechanism and Soil Liquefaction

ABSTRACT Based on undrained cyclic shear experiments conducted on a saturated Ottawa sand in the Torsional Simple Shear Device, the writers propose Eqs. (8) and (10), which respectively pre diet pore-pressure rise in the above soil under uniform and non-uniform dynamic shear stresses. These equations take into consideration the stress loading history, number of stress cycles and stress intensity function. There is excellent agreement between the experimental pore-pressure values and the analytical predictions as shownin Fig. 7 (for uniform) and in Figs. 10, 11, 12, 13 and 14 (for non-uniform) dynamic loadings.