Stress Time History Research Articles

Testing of Models of Flow‐Induced Hemolysis in Blood Flow Through Hypodermic Needles

Hemolysis caused by flow in hypodermic needles interferes with a number of tests on blood samples drawn by venipuncture, including assays for metabolites, electrolytes, and enzymes, causes discomfort during dialysis sessions, and limits transfusion flow rates. To evaluate design modifications to address this problem, as well as hemolysis issues in other cardiovascular devices, computational fluid dynamics (CFD)-based prediction of hemolysis has potential for reducing the time and expense for testing of prototypes. In this project, three CFD-integrated blood damage models were applied to flow-induced hemolysis in 16-G needles and compared with experimental results, which demonstrated that a modified needle with chamfered entrance increased hemolysis, while a rounded entrance decreased hemolysis, compared with a standard needle with sharp entrance. After CFD simulation of the steady-state velocity field, the time histories of scalar stress along a grid of streamlines were calculated. A strain-based cell membrane failure model and two empirical power-law blood damage models were used to predict hemolysis on each streamline. Total hemolysis was calculated by weighting the predicted hemolysis along each streamline by the flow rate along each streamline. The results showed that only the strain-based blood damage model correctly predicted increased hemolysis in the beveled needle and decreased hemolysis in the rounded needle, while the power-law models predicted the opposite trends.

Research on Structural Fatigue Damage Based on the Superimposed Load Spectrum Method

We usually calculate the fatigue damage by superimposed respective injury; the paper brings up the superimposed load spectrum method considering load sequence. It superimposed on the load spectrum of each load and obtained the total damage of total stress time history. Finally, as an example, bolster’s damage is calculated by two ways. By contrast, the damage is larger by former method. The injury results based on the method of superimposed load spectrum is closer to the actual situation. Therefore, the research method presented in this paper can provide a reference for future structural damage.

Simulating the Thermal Response of Glass Under Various Shading Conditions in a Fire

In a fire, the thermal stress upon window glass caused by a temperature difference between exposed and shaded areas is the key factor contributing to glass fracture. The purpose of this study is to investigate the effects of different shaded conditions on the glass when it is exposed to fire. Eleven different shading cases were simulated using finite element method (FEM) software, called EASY, which was developed by the authors and verified accurately by theory. The glass surface temperatures, stress field, the time and location of crack initiation and crack propagation were presented. It was found that the center shaded case is a safer way to protect the glass from cracking and the four corners shaded case has greater probability of cracking. The stress and fracture models for shading glass can be applied in predicting the probability of crack initiation, the distribution variation of temperatures and the stress time history under certain thermal loads. Furthermore, practical advice to optimize the window installation design or ways of shading to protect the glass from falling out in a fire can be obtained from the results.

Upscaling Crack Propagation and Random Interactions in Brittle Materials Under Dynamic Loading

Multi-scale mechanics problems require the use of an appropriate upscaling approach to link micro-scale architecture (e.g., grain structure, defect population, crystal orientation) to macro-scale effective response (e.g., stress, elastoplastic properties, damage). For brittle materials, failure is often associated with crack growth from pre-existing flaws in the material, and with the subsequent coalescence of these cracks. For low strain rates, the simplifying assumption that failure is governed by the largest flaw may be justified. For high strain rates, however, a wider range of the pre-existing flaw population leads to crack initiation prior to failure, making the analysis significantly more complex. Previous analytical models of this high strain-rate behavior apply one of two assumptions: flaws are uniformly sized and periodically located; or, cracks initiated from flaws do not interact. Both of these assumptions are questionable given that these materials are quite heterogeneous at the micro-scale and that fragmentation of these materials exhibit clear crack interactions. Paliwal & Ramesh [1,2] recently addressed this issue by applying a self- consistent model that treats each flaw as residing within an ellipse of pristine (uncracked) material surrounded by a damaged material. In this way, crack growth from each flaw is at least affected indirectly by the presence of cracks from other flaws; however, this model does not address explicit interactions of cracks. In the current research, a probabilistic approach is used to define the proportion of cracks that intersect each other in a given load step. Once two cracks interact, then they are treated as a single larger crack. This model provides a stress-time or stress-strain history at a fixed strain rate loading. Results show that the predictions of strength from the model with explicit crack interactions are reduced from those predicted by the non-probabilistic self-consistent model.

Fatigue behavior of [0n/90n]s composite cantilever beam under tip impulse loading

Vibration induced fatigue analysis of cross-ply [0n/90n]s cantilever beam under tip impulse loading is presented. As a first step, vibration induced stress for the given tip impulse loading was evaluated using modal analysis. Viscous damping model was used for evaluating the stress state as a function of time. The stress-time history was converted into block loading consisting of many sub-blocks. The block loading consisted of four sub-blocks and a total of 135 numbers of cycles. The block loading was repeated after certain time duration. Further, fatigue analysis was performed based on the block loading condition evaluated. Fatigue failure initiation was examined using S–N curve based approach, residual strength approach as well as failure function approach. Number of blocks to failure initiation and the location of failure were obtained. Analysis of cross-ply [0n/90n]s cantilever beam under tip static loading was also conducted for comparison. Studies are also presented using 3D finite element analysis (FEA). Number of blocks required to cause fatigue failure initiation under tip impulse loading was found to be 332 and 331 using the analytical method and 3D FEA, respectively for the geometry of the beam, material properties and loading condition considered.

Analyzing the Influence of Rigid Foundation on Seismic Response of Cable-Stayed Bridge Pylon

Bridges collapses triggered by the earthquake often happen in recent years, and bridge damage caused by the earthquake also results in the great effect due to the secondary disasters. In this paper, we use finite element analysis software ABAQUS to establish the bridge pylon model with rigid-framed pylon bottom to calculate the structural response of two seismic waves (modal analysis, displacement time history, acceleration time history and stress time history of the bridge pylon bottom), comparing the response characteristics of two pylon structures under seismic effect.

Extremely low cycle fatigue prediction of steel beam-to-column connection by using a micro-mechanics based fracture model

Beam-to-column connections in steel moment resisting frames may suffer extremely low cycle fatigue (ELCF) during earthquakes. The cyclic void growth model (CVGM), a micro-mechanics based fracture model, was adopted to predict ELCF fracture of the beam-to-column connections. The validity of the model was verified by the experimental results of nine full-scale connection tests. In addition, refined finite element model was employed to simulate the cyclic behaviors of the connection tests, and the CVGM fracture index was calculated based on the stress and strain time histories. The number of cycles and the cumulative deformations to ELCF fracture predicted by CVGM agreed well with the experimental results. The presented methodology showed reasonable good accuracy to predict ELCF fracture of beam-to-column connection under inelastic cyclic loadings.

3차원 경계요소법과 전선 유한요소 해석의 연성을 통한 전선 유탄성 해석

This paper considers a fully coupled 3D BEM-FEM analysis for the ship structural hydroelasticity problem in waves. Fluid flows and structural responses are analyzed by using a 3D Rankine panel method and a 3D finite element method, respectively. The two methods are fully coupled in the time domain using a fixed-point iteration scheme, and a relaxation scheme is applied for improve convergence. In order to validate the developed method, numerical tests are carried out for a barge model. The computed natural frequency, motion responses, and time histories of stress are compared with the results of the beam-based hydroelasticity program, WISH-FLEX, which was thoroughly validated in previous studies. This study extends to a real-ship application, particularly the springing analysis for a 6500 TEU containership. Based on this study, it is found that the present method provides reliable solutions to the ship hydroelasticity problems.

Catcher Bearing Life Prediction Using a Rainflow Counting Approach

Catcher bearings (CB) are an essential component for rotating machine with active magnetic bearings (AMBs) suspensions. The CB’s role is to protect the magnetic bearing and other close clearance component in the event of an AMB failure. The contact load, the Hertzian stress, and the sub/surface shear stress between rotor, races, and balls are calculated, using a nonlinear ball bearing model with thermal growth, during the rotor drop event. Fatigue life of the CB in terms of the number of drop occurrences prior to failure is calculated by applying the Rainflow Counting Algorithm to the sub/surface shear stress-time history. Numerical simulations including high fidelity bearing models and a Timoshenko beam finite element rotor model show that CB life is dramatically reduced when high-speed backward whirl occurs. The life of the CB is seen to be extended by reducing the CB clearances, by applying static side-loads to the rotor during the drop occurrence, by reducing the drop speed, by reducing the support stiffness and increasing the support damping and by reducing the rotor (journal)—bearing contact friction.

Spectral Formulations for Vortex Induced Vibration Modal Decomposition and Reconstruction

Modal decomposition and reconstruction (MDR) of marine riser vortex induced vibration (VIV) is a technique where vibration is measured using accelerometers and/or angular rate sensors, the modal displacements are solved for and the stress and fatigue damage is reconstructed along the riser. Recent developments have greatly increased the accuracy and reliability of the method. However the computational burden is onerous due to stress time history reconstruction and rainflow cycle counting at every desired location along the riser. In addition, fully synchronous data are required to reconstruct the stress histories. Dirlik’s method for obtaining rainflow damage for Gaussian random stress using only spectral information (four spectral automoments) has proven to be quite accurate with a significant reduction in computational effort. In this paper two spectral formulations of MDR are introduced. The first method is applicable when all the measured data are synchronous. In this method, spectral cross moments of the modal displacements are solved from the spectral cross moments of the measured data using basis vectors consisting of normal mode shapes. The spectral automoments of stress are obtained from the modal displacement cross moments and analytical stress mode shapes. Dirlik’s method is then applied to obtain rainflow damage. The second method is a generalization of the first, where the measured data cross moments are only partially known. This method is applicable when measured data are partially synchronous or asynchronous. A numerical root-finding technique is employed to solve for the modal response cross moments. The method then proceeds in the same manner as the first. The spectral methods are applied to simulated VIV data of a full-scale deepwater riser and to Norwegian Deepwater Program (NDP) scale-model test data on a 38 m long slender riser. Comparisons of reconstructed fatigue damage versus simulated or measured damage indicate that the method is capable of estimating fatigue damage accurately for Gaussian VIV even when data are not fully synchronous. It is also shown that computational cost is greatly reduced.

On the effect of stress intensity factor in evaluating the fatigue crack growth rate of aluminum alloy under the influence of compressive stress cycles

To date, most of the studies conducted on fatigue life estimation of structural components have focused on the Constant Amplitude Loading (CAL) scenarios. However, very few structures in the real world experience such a loading condition, and most structural components undergo a Variable Amplitude Loading (VAL) during their service life. It is also observed that most of the available fatigue crack growth (FCG) models ignore the influence of the compressive stresses, despite the fact that recent studies have highlighted the detrimental effect of compressive stress cycles (CSCs) on the FCG of materials.In this paper, a VAL stress–time history is used to study the fatigue response of 6061-T651 aluminum alloy, with a focus on the compressive portion of the stress time history. An experimental investigation is conducted to assess the influence VAL, in particular, the influence of the CSC on FCG of the material. In the tests, the tensile portion of the stress–time history was kept unchanged, while the compressive portion of the stress–time history were varied by various scaling factors. The experimental results demonstrate that the compressive stress portion of the applied load has a significant influence on the overall fatigue life of the material. It is observed that even introducing a few number of small CSC into the stress–time history can significantly decrease the fatigue life of the material.In addition, the influence of the CSC is also examined by means of a microscopic evaluation of crack surfaces’ roughness.

Effects of wetting and ageing on 1D elasto-viscoplastic behaviour of cement-mixed clay and model simulation

The combined effects of wetting, the viscous property and ageing on the one-dimensional (1D) compression characteristics of kaolin were evaluated. Two series of special constant-rate-of-strain (CRS) 1D compression tests, with sustained loading at intermediate stages, were performed on kaolin with and without cement-mixing. Most of the air-dried specimens were made partially or fully saturated at intermediate stress levels. The effects of the degree of saturation, the wetting process period, the stress level at which wetting was made, the strain rate during loading and the over-consolidation history applied by compaction during the preparation of the specimens were evaluated. The effects of wetting, viscous property and ageing, observed in the experiments, were significant and complicated. A non-linear three-component elasto-viscoplastic model, that had been modified to take into account the effects of wetting, was further modified to account for the ageing effects. The effects of wetting and ageing were described by a decrease and an increase in the inviscid yield stress at a fixed irreversible strain in the plastic component. The viscous property changed from the basic type, Isotach to TESRA as the ageing effects due to cement-hydration developed. The stress–strain relations and the time histories of stress and strain, during complicated loading and wetting histories applied in the experiments, were successfully simulated by the modified model.

Equivalent Fatigue Stress Analysis of the Key Parts of Railway RD<sub>2</sub> Axle

Nonlinear dynamics model of the C62freight car was established firstly and the random load spectrum acted on the wheelset was obtained by the simulation of the freight car running on a typical line. Taking the cyclic constructive relation of LZ50 axle steel into account in the finite element analysis of the wheelset, the stress time histories of the key parts of the axle in some typical conditions were got. Furthermore, based on the stress spectrum analysis of the hazard sections of the axle, the probabilistic fatigue stress spectrums with given probability and confidence were obtained. Finally, combining with the linear cumulative damage rules, the stress distribution of RD2axle was investigated, which is fundamental for the further prediction of the fatigue life of axle.

Dynamic Analysis and Design Method Study on the Combined-Boom System of Portal Crane

As a main handling device the portal crane is widely used in port, railroad, etc.The crane handling procedure is mainly carried out through its combined-boom system luffing or swing .In general, in order to reduce drive power and improve the operational performance, the luffing trajectory should meet the design requirement. At the same time, structure stress should be secured in the whole process of handling the cargo. Recently, to deal with more heaver and further cargo, the portal crane is becoming more large-scale. So that the large-scale components such as jib elastic deformation effect on large displacement motion cannot be ignored longer. In addition to the structure high speed motion in the process of handling also make the structure dynamic behaviors spending more obvious specially in the condition of luffing combined with swing. However, the problem for this dynamic behavior brings about to physical design sometimes has no method to solve according to the conventional analysis algorithm and dynamics method. To reduce the deviation caused by the common analysis, design and analysis method based on the multibody is put forward in this thesis. According to the method, the result on the luffing trajectory and stress-time history are analyzed easily. So that it ensure the efficiency and increase the accuracy of the initial design according to the conventional design and analysis method.

Fatigue assessment of multi-loading suspension bridges using continuum damage model

Long-span steel suspension bridges carrying both highway and railway have been built in wind-prone regions. The fatigue assessment of such bridges under the combined action of railway, highway, and wind loading represents a challenging task in consideration of uncertainties in both fatigue loading and fatigue resistance. This paper presents a framework for fatigue assessment of a long-span suspension bridge under combined highway, railway, and wind loadings using a continuum damage model. The continuum damage model (CDM) is first established based on continuum damage mechanics with an effective stress range and an effective nonlinear accumulative parameter to represent all of the stress ranges within a daily block of stress time history of the bridge. The CDM is then applied to estimate damage accumulation of the Tsing Ma suspension bridge at fatigue-critical locations, and the results are compared with those estimated by the linear Miner’s model. A limit state function for fatigue reliability analysis based on CDM is also defined by introducing proper random variables into CDM. The Monte Carlo simulation (MCS) is then adopted to generate the random variables and to calculate failure probability. Finally, the failure probabilities of the Tsing Ma Bridge at the end of 120years are estimated for different loading scenarios. The results demonstrate that the fatigue condition of the Tsing Ma Bridge at the end of its design life depends on loading scenarios.

An equivalent stress process for fatigue life estimation under multiaxial loadings based on a new non linear damage model

Abstract Fatigue life estimation or fatigue damage evaluation of mechanical components under a multiaxial state of stress time-history has an important role in virtual design phases, but this evaluation is a real problem to resolve, because this goal is not reached by classical fatigue criteria. In this context, the equivalent uniaxial stress has been chosen as the approach useful for this purpose by combining it with a strength curve for the material (i.e. S – N curve) and damage evaluation (Damaged Stress Model (DMS) and Miner's rule). So the authors have taken equivalent stresses based on a multiaxial criterion that can be used as a uniaxial stress time history for the application of damage evaluation methods to predict the fatigue life, under multiaxial random loading. The cycles were counted with the Rain Flow algorithm, using equivalent stress as a variable counting. In the case of “asymmetric” histories, the algorithm of transformation of the stress history (because of its global expected value different from zero) is required. In the case of 10HNAP steel, stress amplitude transformation according to the Goodman relationship gives good results. The proposed algorithm was verified during fatigue tests of cruciform specimens made of 10HNAP steel, subjected to biaxial non-proportional random tension-compression.

Analysis of C80B Wagon’s Load-Stress Transfer Relation

In this paper, C80B car body is the research object to study the load-stress transfer relationship that has great influence on the car body structure. First of all, through the test data of line DaTong to Qin Huangdao, the load-time history of C80B car body’s load on center plate, load on draw gear, roll load and torsional load have been obtained, as well as the stress-time history of the body fatigue key parts have been obtained. And the load spectrum and stress spectrum have been made up. Then the finite element analysis of the car body is made. The load-stress transfer coefficient of fatigue key parts on car body could be obtained. Last the load and stress transfer relationship in detail considering the measured data has been analyzed.

EQUALIZING IRREGULAR EARTHQUAKE LOADING TO HARMONIC LOADING FOR LIQUEFACTION STUDY

Liquefaction triggered by earthquakes is a source of damage to structures resting on loose to medium sandy soils. During earthquakes soil structures and the ground are subjected to vibratory excitations which are to a high degree erratic and extremely irregular. The magnitude of shear stress that is applied to a soil element in a real earthquake will, therefore, vary at random from one second to another. In order to evaluate the effect of such randomness, averaging procedures have been employed. In this averaging method a complex stress time history can be converted to an equivalent number of constant harmonic stress cycles. The equivalent load pattern thus determined has been considered as a representative load. This concept tends itself considerably to the simplification of the laboratory method. The soil selected for this thesis is known as Firouzkouh Sand No. 161, that exerted by load pattern that recorded in Kojaeli earthquake in 1999. Finally by using the stress averaging method, the reduction coefficient of stress is proposed and compared to those of existing studies and codes.

Fatigue analysis of long-span suspension bridges under multiple loading: Case study

Long-span suspension bridges are often subject to multiple types of dynamic loads, especially those located in wind-prone regions and carrying both trains and road vehicles. Fatigue assessment shall be performed to ensure the safety and functionality of the bridges. This paper proposes a framework for fatigue analysis of a long-span suspension bridge under multiple loading by integrating computer simulation with structural health monitoring system. By taking the Tsing Ma Bridge in Hong Kong as an example, a computationally efficient engineering approach is first proposed for dynamic stress analysis of the bridge under railway, highway and wind loading. The fatigue-critical locations are then determined for key bridge components, and databases of the dynamic stress responses at the critical locations are established. The time histories of dynamic stresses induced by individual loading during the design life of the bridge are generated based on the databases. The corresponding stress time histories due to the combined action of multiple loading are also compiled. Finally, fatigue analysis is performed to compute the cumulative fatigue damage over the design life of 120 years. The results indicate that it is necessary to consider the combined effect of multiple loading in the fatigue analysis of long-span suspension bridges.

Generation of correlated stress time histories from continuous turbulence Power Spectral Density for fatigue analysis of aircraft structures

The main purpose of the present work is to develop an efficient computational method for generating correlated stress time histories for aircraft structures under gust loads. Random gusts in any direction, which lead to random multiaxial loads on the aircraft structure are considered. A direct temporal simulation of stress using a finite element model is not possible due to computational burden. In order to overcome this, a new and efficient method based on Power Spectral Density functions (PSD) of stress is proposed. Since the PSD of the various stress components have not previously been correlated, a result enabling the direct generation of the correlation between them has been established, which is crucial for fatigue and damage tolerance analysis in several dimensions. Validation is performed by comparison with a direct (and costly) temporal simulation as well as Rice’s formulas. An example on a long range aircraft illustrates the relevance of the proposed approach. Although this method is presented with an application on a two dimensional stress tensor, it should be noted that it could be straightforwardly extended to any linear system with multiple input and output.