Dynamic Stress Analysis Research Articles

TDI CAMERA APPLICATION IN DYNAMIC PHOTOMECHANICS

Optical methods for dynamic stress analysis require fast recording of the fringe patterns representing the stress distribution. Various recording techniques exist using fast framing cameras and short light pulse systems.1 In all of these techniques the wet film processing is tedious and time consuming. Manual data analysis from the fringe patterns is cumbersome. Also, optical processing of the photographs for extracting further information requires complicated optical hardware. Hence, there were efforts from researchers to record the patterns in computer memories. The software image processing methods ease the data analysis and contrast enhancement.2,3 Here we report the use of a special type CCD camera for dynamic applications. Details of the CCD camera operation are discussed. Application of the camera for dynamic problems is illustrated by performing a simple experiment.

Failure analysis of an exploded gas cylinder

This paper reports the major activities carried out during the failure analysis of an exploded cylinder containing hydrogen. The general cracking pattern of the cylinder, the fractographic features, and the stress analysis results were all indicative of an internal gaseous detonation. Accordingly, several specific characteristics of detonation-driven fracture of closed-end cylindrical tubes were identified. These characteristics were analyzed through detailed examinations of the fracture surfaces, cracking patterns, and dynamic stress analysis of the cylinder using a transient analytical model. Based on the size and location of special markings found on the shear lips, and using the time duration of flexural waves, the crack growth increments and speed were computed. Consequently, the basic features of the gaseous detonation and the composition of the original gas mixture were identified. The results indicated that the detonation of a low-pressure oxygen-rich mixture of hydrogen and oxygen was the cause of this failure. The presence of oxygen was attributed to an improper usage of an oxygen cylinder for hydrogen storage.

Computer model validation with functional output

A key question in evaluation of computer models is Does the computer model adequately represent reality? A six-step process for computer model validation is set out in Bayarri et al. [Technometrics 49 (2007) 138–154] (and briefly summarized below), based on comparison of computer model runs with field data of the process being modeled. The methodology is particularly suited to treating the major issues associated with the validation process: quantifying multiple sources of error and uncertainty in computer models; combining multiple sources of information; and being able to adapt to different, but related scenarios. Two complications that frequently arise in practice are the need to deal with highly irregular functional data and the need to acknowledge and incorporate uncertainty in the inputs. We develop methodology to deal with both complications. A key part of the approach utilizes a wavelet representation of the functional data, applies a hierarchical version of the scalar validation methodology to the wavelet coefficients, and transforms back, to ultimately compare computer model output with field output. The generality of the methodology is only limited by the capability of a combination of computational tools and the appropriateness of decompositions of the sort (wavelets) employed here. The methods and analyses we present are illustrated with a test bed dynamic stress analysis for a particular engineering system.

Analysis of the dynamic stress of planar flexible-links parallel robots

This paper presents a method for the dynamic stress analysis of planar parallel robots with flexible links and a rigid moving platform. The finite element-based dynamic model of flexible parallel robots is proposed. The relation between elastic deformations and elastic displacements of the flexible links is investigated, considering the coupling effects of elastic motion and rigid motion. The elastic deformations of links are calculated. Considering the effects of bending-shearing strain and tensile-compression strain, the dynamic stress of the links and its position are derived by using the Kineto-Elastodynamics theory and the Timoshenko beam theory. Due to the flexibility of the links, the dynamic stresses are well illustrated through numerical simulation. Compared with the results of the finite element software SAMCEF, the numerical simulation results show the good coherence and advantages of the analysis method. The dynamic stress analysis is demonstrated to have a significant impact on the analysis, design and control of flexible parallel robots.

Damage prediction in composite plates subjected to low velocity impact

Abstract In this investigation, fiber-reinforced composite plates subjected to low velocity impact are studied by the use of finite element analysis (FE). Mindlin’s plate theory is implemented into the FE approach in which a 9-node Lagrangian element is considered. Dynamic stress analysis is carried out by the use of a constitutive equation of composite laminates without damage. A parametric analysis shows that the increase in the percentage of the 90° plies increases the contact force implying a reduction in the rigidity of the laminate. Stresses are calculated at nine Gaussian points of each element of each interface and then averaged. At first, threshold velocities are evaluated for different stacking sequence to predict matrix crack initiation. Then, the impact induces damage at a higher impact velocity including matrix cracking is predicted by the appropriate failure criteria. The present results indicate that matrix cracking appears in the upper 90° plies with the dominance of transverse shear stress.

Dynamic stress analysis of rail joint with height difference defect using finite element method

A finite element analysis is conducted to study dynamic elastic–plastic stress when a wheel passes a rail joint with height difference between the two sides of a gap. The ANSYS implicit code and LS-DYNA explicit code are coupled to simulate the process of the wheel contacting or impacting the rail joint. Contact elements are used to simulate the interactions between wheel and rails, between rails and joint bars, between joint bars and bolts and between bolts and rails. The effects of train speed, axle load and height difference on the contact forces, stresses and strains at railhead are investigated. Numerical results show that the presence of rail joint with height difference significantly affect the contact force, stress and strains. The results also indicate that the train speed has a larger effect on the contact force, stress and strains than the axle load.

Numerical Analysis of Dynamic Thermal Stress by Extended Distinct Element Method

This paper presents the numerical analysis of dynamic thermal stresses by the extended distinct element method (EDEM), which is a kind of the meshless methods. The new technique which radii of the elements of the EDEM are changed with the temperature of each element is proposed. The temperature of the element is calculated on the basis of the heat conduction between elements. By the comparison between the analytical result of Sternberg and Chakravorty and the numerical result obtained by the proposed method, it was confirmed that the method was effective for the dynamic thermal stress analysis. Numerical examples were also presented for the cases of a non-homogeneous plate subjected to the surface heating and a glass block with an initial crack subjected to the surface heating. From these numerical results, it was found that the method based on the EDEM is an efficient tool for analysis of dynamic thermal stresses.

Three-Dimensional Dynamic Fracture Analysis Using the Material Point Method

This paper describes algorithms for threedimensional dynamic stress and fracture analysis using the material point method (MPM). By allowing dual velocity fields at background grid nodes, the method provides exact numerical implementation of explicit cracks in a predominantly meshless method. Crack contact schemes were included for automatically preventing crack surfaces from interpenetration. Crack-tip parameters, dynamic J-integral vector and mode I, II, and III stress intensity factors, were calculated from the dynamic stress solution. Comparisons to finite difference method (FDM), finite element method (FEM), and boundary element method (BEM), as well as to static theories showed that MPM can efficiently and accurately solve three-dimensional dynamic fracture problems. Since the crack description is independent of the object description, MPM could be useful for simulation of threedimensional dynamic crack propagation in arbitrary directions. keyword: Material point method, MPM. threedimensional dynamic fracture, cracks, dynamic J-integral, dynamic stress intensity, contact, mode I, mode II, mode III.

Elastic Transverse Impact on Beams

Present investigation were carried out to study photoelastically the stress distributions in a simply supported beam with over- hangs subjected to a low velocity central- and quarter- spanimpact loadings by light strikers keeping beam/ striker weight ratio constant (2.675), and then comparing the results so obtained with those in similar simply supported beams made of other materials subjected to central- impact loadings from an analysis of dynamic strain gauge data. Interesting new findings were obtained from the results of the present investigation and also from results reported in the literature in this respect. Introduction. In modern times dynamic stress analysis is becoming increasingly important for various engineering applications. Although significant amount of insight in these respects have been developed, the subject being rather intricate would continue to attract of more research workers in future. A beam is a common structural element, and in several applications, simply supported beams with over- hang are employed in practice. Transverse and longitudinal bridge girders and chassis of rails- and road- wagons are some of the typical applications of the same. Here, photoelastic technique was employed to determine dynamic stress distributions in a model simply supported beam with over- hang.

Dynamic Stress Analysis Method and Its Application for Urethane Wheels Using the Computer Model

An Over Head Transportation (OHT) vehicle is used to transport large loads in a factory more efficiently. To maximize productivity, the speed and load requirement for the OHT vehicle is continually increasing. This may create a repetitive dynamic load and thus cause fatigue failure in related components. In this paper, a computer aided engineering (CAE) method is proposed for fatigue life prediction in the early design stage using multibody dynamic analysis and the linear damage rule. The process of predicting the fatigue life using the proposed computer models in this paper may be applied to structures of various mechanical systems.

A flexible multi-body dynamic model for analyzing the hysteretic characteristics and the dynamic stress of a taper leaf spring

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of 1–2 mm/sec and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

Fluid structure interaction of patient specific abdominal aortic aneurysms: a comparison with solid stress models

BackgroundAbdominal aortic aneurysm (AAA) is a dilatation of the aortic wall, which can rupture, if left untreated. Previous work has shown that, maximum diameter is not a reliable determinant of AAA rupture. However, it is currently the most widely accepted indicator. Wall stress may be a better indicator and promising patient specific results from structural models using static pressure, have been published. Since flow and pressure inside AAA are non-uniform, the dynamic interaction between the pulsatile flow and wall may influence the predicted wall stress. The purpose of the present study was to compare static and dynamic wall stress analysis of patient specific AAAs.MethodPatient-specific AAA models were created from CT scans of three patients. Two simulations were performed on each lumen model, fluid structure interaction (FSI) model and static structural (SS) model. The AAA wall was created by dilating the lumen with a uniform 1.5 mm thickness, and was modeled as a non-linear hyperelastic material. Commercial finite element code Adina 8.2 was used for all simulations. The results were compared between the FSI and SS simulations.ResultsResults are presented for the wall stress patterns, wall shear stress patterns, pressure, and velocity fields within the lumen. It is demonstrated that including fluid flow can change local wall stresses slightly. However, as far as the peak wall stress is concerned, this effect is negligible as the difference between SS and FSI models is less than 1%.ConclusionThe results suggest that fully coupled FSI simulation, which requires considerable computational power to run, adds little to rupture risk prediction. This justifies the use of SS models in previous studies.

Estimation of Service Life of Aged Continuous Welded Rail

This article presents fatigue tests conducted on aging continuous welded rails (CWR) in order to estimate the service life of the rails. This was done in order to prepare a dynamic stress analysis model for welded joints with boltholes. Such an analysis is useful for re-estimating rail life due to reduced vehicle weight and better jointures that operators have experienced in recent years. This also included the anticipated result of extending the period of replacement for such rails. The tests conducted used a beam model that allowed for the analysis of dynamic wheel/rail contact and interface forces in addition to a solid model that was used to analysis stress fields based on those forces. Dynamic stress analysis indicated that the specified model's testing is valid as checked against field tests. The extension of service life for CWRs was deemed safe by the test with the proviso that such welds would need to be accompanied by the grinding of surface irregularities.

406 骨粗鬆症脊椎の衝撃解析における荷重条件の影響(OS4-2,オーガナイズドセッション4:生体のモデリング・シミュレーション・計測,学術講演)

406 骨粗鬆症脊椎の衝撃解析における荷重条件の影響(OS4-2,オーガナイズドセッション4:生体のモデリング・シミュレーション・計測,学術講演)

540 有限要素法による人工股関節の動的応力解析(S09-2 関節のバイオメカニズム(2),S09 関節のバイオメカニズム)

540 有限要素法による人工股関節の動的応力解析(S09-2 関節のバイオメカニズム(2),S09 関節のバイオメカニズム)

진동 해석을 통한 300 MW급 저압터빈 블레이드의 손상 원인 규명

The failure of blades frequently happened in the 300 MW LP(low pressure) turbine until now and they are maintaining the blades periodically during outage. So the blade-disk system is analysed by FEM in order to identify the main cause of failure of blade row. It is found that the stress of root's hole is highest in comparison with other parts from the result of the steady stress analysis. Also, the two dangerous frequencies which is related to the resonance condition are found in the interference diagram. One is 1,316 Hz. The other is 2,981 Hz which is related to the 1 nozzle passing frequency. The dynamic stress analysis is performed to identify more accurate root cause for failure of blade row It is confirmed that the dynamic stress of the former is higher than one of the latter From these results, it is concluded that the former has deeply something to do with the failure of blades more than the tatter. Based on versatile investigation and deliberation, the change of blade's grouping is determined to avoid the resonance condition with the operating speed. After the blade grouping is changed, the former frequency vanish completely but the latter is still in existence in the interference diagram. Fortunately, It is confirmed that the dynamic stress of the new blade grouping is lower than one of the old blade grouping. 2 years has passed since modification and the LP turbine is operated well without failure so far.

Effect of proton beam profile on stress in JSNS target vessel

A cross-flow type (CFT) mercury target with flow guide blades has been developed for JSNS that suppresses the generation of a stagnant flow region near the beam window where the peak power density is generated due to the spallation reaction. In addition, a flat type beam window has been applied to the CFT target that suppresses dynamic stress caused by pressure waves, that have been estimated with an elastic model for mercury. Recent experimental results obtained by using a proton beam incident to mercury targets suggested that using a cut-off pressure model for mercury would be appropriate for predicting a dynamic stress behavior in a target vessel. Dynamic stress analyses were carried out with the cutoff pressure model in which the negative pressure less than −0.15 MPa could not be sustained. The dynamic stress generated in the flat beam window became much larger than that in a semi-cylindrical type window as a result of using the cut-off pressure model. Regardless, even the stress generated in the semi-cylindrical type beam window exceeded the allowable stress of SS316L under the peak power density of 668 MW/m 3. In order to decrease the dynamic stress in the semi-cylindrical beam window, the incident proton beam was defocused to reduce the peak power density down to 218 MW/m 3. Although the dynamic stress could be suppressed to less than the allowable stress, the high power density generated on the end of the flow guide blades due to defocus of the proton beam caused high thermal stress exceeding the allowable stress. Several shapes of blade ends were studied analytically to decrease the thermal stress, that did not affect the mercury flow distribution. A simple thin-end blade showed low thermal stress below the allowable stress.

On dynamic stress analysis for cracks in elastic materials with voids

The present paper is concerned with the development of a semi-analytical approach to the dynamic problem of the concentration of stresses near the edges of a crack located in a porous elastic space (two-dimensional problem) and subjected to a normal oscillating load applied to the crack faces. Our analysis is made in the context of the Goodman–Cowin–Nunziato (G–C–N) theory for porous media. In previous work we studied static crack problems for such materials; now we introduce an analysis of the relevant dynamic aspects. By using the Fourier transform, the problem is reduced in explicit form to a hyper-singular integral equation with a convolution kernel valid over the crack length. Then, we apply a collocation technique developed in our previous work to solve this equation, and study the stress intensity factor. The principal goal is to compare the stress intensity factor for the static and dynamic cases. We also compare our results with the case of an ordinary linear elastic medium.

Dynamic Analysis of Stresses and Evaluation of Service Life of Jointed Rails

Jointed rails are replaced periodically in Japan. Their service life is governed mainly by the fracture at the joints. To evaluate the fatigue life of jointed rails, it is necessary to verify the stress distribution around fish-bolt holes and an S-N curve of jointed rails. Therefore, we carried out static loading tests in a laboratory and field tests to measure the stresses around the fish-bolt holes, and further dynamic stress analysis of jointed rails and bending fatigue tests of rails used in the field.The dynamic stress analysis model is composed of a beam model to calculate dynamic wheel/rail contact forces and a solid model to calculate stress distribution resulting from those contact forces. These models were validated using field test data. Based on the study results, we established a method to evaluate the fatigue life of jointed rails. In this method, we calculated the stresses under several combined conditions of jointed rail, vehicle type and vehicle speeds.The fatigue life was calculated by applying the stresses to the S-N curve. As a result, the rail replacement period have a potential to be extended except in cases of heavy wear between a fishplate and rail.

Calculation of J-Integral and Stress Intensity Factors using the Material Point Method

The Material Point Method (MPM), which is a particle-based, meshless method that discretizes ma- terial bodies into a collection of material points (the par- ticles), is a new method for numerical analysis of dy- namic solid mechanics problems. Recently, MPM has been generalized to include dynamic stress analysis of structures with explicit cracks. This paper considers eval- uation of crack-tip parameters, such as J-integral and stress intensity factors, from MPM calculations involv- ing explicit cracks. Examples for both static and dynamic problems for pure modes I and II or mixed mode loading show that MPM works well for calculation of fracture parameters. The MPM results agree well with results ob- tained by other numerical methods and with analytical solutions. keyword: Material point method (MPM), dynamic fracture, J integral, stress intensity factor.