Dynamic Strength Evaluation Research Articles

Dynamic simulation of nozzle structure based on thermal-fluid-solid coupling analysis

Many engineering structures are subjected to the combined action of thermal field, flow field and vibration load during use. The mechanical analysis of this kind of structure has important theoretical significance and engineering practical value. However, due to the complexity of multi-field coupling, it is difficult to analyze dynamic response and dynamic strength. A method to simplify the thermal-fluid-solid coupling model for specific engineering issues was proposed aiming at modeling the actual situation in which the high temperature field of the engine nozzle structure is relatively stable. Heated grid reconstruction, thermal modal analysis technology, and fluid-structure coupling response calculation method based on modal superposition were taken to obtain the load distribution and dynamic response level of the engine nozzle structure under the condition of thermal-fluid-solid coupling, which created conditions for structural dynamic strength evaluation including the prediction of vibration fatigue life. The test structure of an engine nozzle was taken as an example to perform dynamic response calculation and fatigue life prediction under thermal fluid-solid coupling conditions. Then the location of weak parts of the structure was identified, and effective suggestions for design improvement was put forward. Compared with the actual test results, the feasibility and accuracy of the method are preliminarily verified.

A probabilistic approach to evaluate dynamic and static strength of quasi-brittle materials through high-rate testing

Results of mechanical tests, especially in dynamics, obtained under similar input conditions always have a statistical scatter. Currently, there is no generally accepted engineering approach to the correct assessment of critical stresses for a material under dynamic loads. For example, there is no clear understanding of how many specimens need to be tested to estimate a specific ultimate stress for a specific impact rate. The present study enhances the applicability of the randomized algorithm of Sign-Perturbed Sums to solve the mentioned problem of the dynamic strength evaluation under typical restrictions on experimental results such as few numbers of data points with unknown random noises. The combination of the incubation time criteria and this new probabilistic approach permits to estimate accurately material strength parameters: the critical failure stress and the incubation time with a given level of confidence. Comparative analysis of developing approach and different modifications of the scaling law obtained by Kimberly and Ramesh showed that both models are well agreed with empirically observed data. Experimental data of dynamic test on split Hopkinson pressure bars and a drop tower setup for different quasi-brittle materials are taken to demonstrate advantages of the new method. It is shown that incubation time of failure and critical stress values of certain materials can be estimated with a high level of confidence. These results can be used to optimize experimental studies and develop new standards for dynamic testing of materials.

Dynamic model updating based on strain mode shape and natural frequency using hybrid pattern search technique

Aiming at providing a precise dynamic structural finite element (FE) model for dynamic strength evaluation in addition to dynamic analysis. A dynamic FE model updating method is presented to correct the uncertain parameters of the FE model of a structure using strain mode shapes and natural frequencies. The strain mode shape, which is sensitive to local changes in structure, is used instead of the displacement mode for enhancing model updating. The coordinate strain modal assurance criterion is developed to evaluate the correlation level at each coordinate over the experimental and the analytical strain mode shapes. Moreover, the natural frequencies which provide the global information of the structure are used to guarantee the accuracy of modal properties of the global model. Then, the weighted summation of the natural frequency residual and the coordinate strain modal assurance criterion residual is used as the objective function in the proposed dynamic FE model updating procedure. The hybrid genetic/pattern-search optimization algorithm is adopted to perform the dynamic FE model updating procedure. Numerical simulation and model updating experiment for a clamped-clamped beam are performed to validate the feasibility and effectiveness of the present method. The results show that the proposed method can be used to update the uncertain parameters with good robustness. And the updated dynamic FE model of the beam structure, which can correctly predict both the natural frequencies and the local dynamic strains, is reliable for the following dynamic analysis and dynamic strength evaluation.

Boundary Condition Simulation for Structural Local Refined Modeling Using Genetic Algorithm

Structural dynamic strength evaluation is paid more attentions in aeronautics and astronautics engineering, and the structural local refined modelling technique which can be utilized to precisely calculate the dynamic strains in the critical local sites of the structure is the key issue in the structural dynamic strength evaluation. Firstly, four common methods, i.e. global / local two-step method, substructure method, transition element method and multi-point constraint (MPC) method, used in structural local refined modeling was reviewed. Then, a structural local refined modeling method, which uses simple physical models to simulate the effect of the surrounding structure on the local structure, is proposed based on Genetic Algorithm (GA). Finally, the proposed structural local refined modeling method was illustrated by simulative example of a four edges fixed aluminum rectangular plate.

Dynamic Fracture Behavior of the Martensitic High Strength Steel after Spot Welding

Martensitic low alloy high strength steel grade of 22MnB5, used for automotive safety parts constructions, was subject of the experimental analyses of dynamic fracture behavior. The main purpose of the performed analyses was the qualitative and quantitative evaluation of heterogeneities due to the standard spot welding technology. The dynamic resistance of heat affected zones compared to uninfluenced martensitic steel were the subject of suggested methodology for the evaluation of dynamic strength; impact tensile tests were performed after simulation of heat affected zone. Dynamic strength, energy consumption and fracture mode were evaluated at different strain rate. This allows to sketch the influence of the strain rate on the weld joint load capacity. Structural and fractography analyses were focused on an induced degradation process in terms of phase transformation and fracture mode.

Static and dynamic strength evaluation of interference fit and adhesively bonded cylindrical joints

The present work aims at defining the anaerobic adhesive residual strength in drive-fit and adhesively bonded cylindrical joints, loaded with a tension–tension fatigue cycle. The final purpose is to evaluate the possibility of reducing the interference level by taking advantage of the adhesive strength. The tested specimens are some shaft hub cylindrical joints made of different materials: the hubs are always made of steel alloy whereas the shafts are made both of steel alloy and of aluminium alloy. Firstly, some coupling and decoupling tests have been performed in order to evaluate the static strength of the joints, calculated as the addition of the interference contribution with the adhesive contribution. Then, the fatigue tests have been carried out in order to evaluate the adhesive residual strength after 10 6 tension–tension fatigue cycles. The fatigue cycles have been related to the static strength of the joint. The mechanical behaviour of steel–steel couplings has been observed to be strongly different from the aluminium–steel ones.

Study on Dynamic Strength Evaluation Method of Mechanical Members Based on Energy Balance

In Japan, mechanical structures installed in nuclear power plants, such as piping and equipment, are usually designed statically in an elastic region. Although these mechanical structures have sufficient seismic safety margin, understanding the ultimate fatigue endurance is very important in order to improve the seismic safety reliability for unexpected severe earthquakes. Moreover, clarifying a margin of seismic resistance of mechanical structures that suffered a severe earthquake is being required. In this study, the energy balance equation that is one of valid methods for structural calculation is applied to the above-mentioned issues. The main feature of the energy balance equation is that it explains accumulated information of motion. Therefore the energy balance is adequate for the investigation of the influence of cumulative load such as seismic response. The investigation is implemented by forced vibration experiments. The experiment models are simple single–degree-of-freedom models that are made of stainless steel and carbon steel. In the experiment, random waves having predominant frequency similar to natural frequency of the experimental model are input in order to obtain adequate response not only in the elastic region but also in the plastic region. As a result, experimental models vibrate under resonance condition, so response acceleration is approximately seven times as big as the input. The excitation is continued until the experimental models fracture, and is carried out with various input levels. In the experiment, models suffered cracks at the bottom end, and fractured finally. As a result, input energy for failure increases as time for failure. In other words, more input energy for failure is needed in case of small input. Moreover the correlation between increment in input energy and input energy for failure is investigated. It was confirmed that input energy for failure is inversely proportional to increment in input energy per unit time. Additionally energy for failure of stainless steel is about twice as big as carbon steel. The correlation between fatigue failure and energy is confirmed from the vibration experiment. Therefore it is expected that time for fatigue failure can be evaluated by the energy balance equation.

The relationship between work function and low back pain history in occupationally active individuals

Purpose. To investigate the relationship between work function and low back pain (LBP) history.Study design. Cross-sectional study.Background. In some countries, traditional medical examinations do not assess work performance in people who continue working despite a history of LBP, although such assessment may be required.Methods. A total of 100 industrial metal workers were assigned to groups with and without LBP history. Logistic regression and t-tests examined the associations between physical work performance (represented by dynamic strength evaluation) and the group, and compared worker performance between the two groups. Similar tests examined potentially confounding effects on group assignment.Results. Work performance was significantly associated with the group in dynamic strength sub-tests assessing weight lifting and carrying. The weights handled were lower in the group with LBP history (p < 0.05). Only the workers' country of origin affected group assignment; adjustment for this factor, as well as for age and education improved the associations between work performance and the group.Conclusions. Workers with a history of LBP display decreased physical performance at work, which should be subject to further research and treated as a health-related problem in accordance with the ICF model.

Dynamic strength evaluations for self-piercing rivets and resistance spot welds joining similar and dissimilar metals

This paper summarizes the dynamic joint strength evaluation procedures and the measured dynamic strength data for 13 joint populations of self-piercing rivets (SPR) and resistance spot welds (RSWs) joining similar and dissimilar metals. A state-of-the-art review of the current practice for conducting dynamic tensile/compressive strength tests in different strain rate regimes is first presented, and the generic issues associated with dynamic strength test are addressed. Then, the joint strength testing procedures and fixture designs used in the current study are described, and the typical load versus displacement curves under different loading configurations are presented. Uniqueness of the current data compared with data in the open literature is discussed. The majority of experimental results indicate that joint strength increases with increasing loading rate. However, the strength increase from 4.47 m/s (10 mph) to 8.94 m/s (20 mph) is not as significant as the strength increase from static to 4.47 m/s. It is also found that with increasing loading velocity, displacement to failure decreases for all the joint samples. Therefore, ‘brittleness’ of the joint sample increases with impact velocity. Detailed static and dynamic strength data and the associated energy absorption levels for all the samples in the 13 joint populations are also included.

Static and dynamic strength evaluation of the hand and wrist following proximal row carpectomy: volar vs dorsal approach

Static and dynamic strength evaluation of the hand and wrist following proximal row carpectomy: volar vs dorsal approach

Use of fibrinolytic (urokinase) and anti-coagulant (enoxaparine) for the salvage of replanted digits

Use of fibrinolytic (urokinase) and anti-coagulant (enoxaparine) for the salvage of replanted digits

Evaluation of Dynamic Strength of Concrete from Results of Static Tests

The main purpose of the present study is to investigate the possibility to predetermine the strength of concrete at different strain rates and cyclic loading. Particular emphasis is placed on describing the method of estimating the dynamic strength of concrete from results of monotonic tests. One approach to solving this problem is based on making allowance for the kinetic nature of fracture, i.e., taking into account that the failure of building materials (metals, glasses, polymers, composites, etc.) under loading is not a critical event but rather is the result of a process of nucleation, accumulation, and the development of damage elements. At the atomic-molecular level, this process is controlled by events of breaking of interatomic bonds by thermal fluctuations. Comparing the given physically justified method with experiments shows that developed methods of diagnostics of dynamic characteristics are sufficiently accurate to make it possible to decrease the labor input of measurements, and do not requ...

Dynamic strength evaluation of gravelly soils : Tanaka, Y; Kokusho, T; Yoshida, Y; Kudo, K Proc Discussion Session on Influence of Local Conditions on Seismic Response, 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 18 August 1989P113–120. Publ Tokyo: JSSMFE, 1989

Dynamic strength evaluation of gravelly soils : Tanaka, Y; Kokusho, T; Yoshida, Y; Kudo, K Proc Discussion Session on Influence of Local Conditions on Seismic Response, 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 18 August 1989P113–120. Publ Tokyo: JSSMFE, 1989

Dynamic Strength Evaluation of Ceramic Circular Beams Containing Small Flaws

A method for the dynamic strength evaluation of ceramic beams containing small flaws was studied, and the following were observed: (1) With an increase in the taper ratio, the eigenvalue of the first order decreases, while the eigenvalues of the second, third and fourth orders increase. With an increase in the opening angle, the eigenvalue decreases monotonically. (2) The critical frequency range is obtained by evaluating the beam strength on the basis of the static fatigue limit. (3) The critical frequency range increases gradually with an increase in the equivalent crack length. (4) With an increase in the damping ratio, the critical frequency range of each order is nearly constant, and then decreases until it disappears. The critical frequency range of lower order is less affected by the damping ratio.

Dynamic Strength Evaluation of Ceramic Beams Containing Small Flaws

Dynamic Strength Evaluation of Ceramic Beams Containing Small Flaws

Dynamic strength evaluation of ceramic circular beams containing small flaws.

A method for dynamic strength evaluation of ceramic circular beams containing small flaws was studied. (1) With an increase in the ratio of breadth and depth, the eigenvalues increased, except for the fundamental eigenvalue. The eigenvalues decreased monotonically, with an increase in the opening angle. (2) The critical frequency range was obtained by evaluating the strength of beams on the basis of the static-fatigue limit. (3) The critical frequency range increased slightly, with an increase in the equivalent crack length. (4) For an increase in the damping ratio, the critical frequency range was constant, and then became smaller. The fundamental critical frequency range was not affected by the damping ratio.