Dynamic Fatigue Strength Research Articles

Development of a Generalized Mathematical Model for Slider-Crank Mechanism Based on Multiobjective Concurrent Engineering with Application

A design optimization of a slider-crank mechanism (SCM) based upon multiobjective concurrent engineering is presented in this paper. The proposed generalized mathematical model includes geometric equations, kinetic–dynamic expressions, fatigue strength and stability requirements and allows to take into consideration the manufacturing capabilities available. The model also allows for describing the actual mechanism characteristics and can be used directly for the detailed design stage of SCMs, in contrast to the simplified physical models available for preliminary design. Based on this approach, the multiobjective model of SCM which includes 11 variables, seven constrained expressions and the three most important objective functions (total mass, required power and maximum dynamic reaction) was developed. The closed-form analytical expressions were established to the relationship between objective functions, constraints and variables. The correctness of the model was checked by using the finite element method. By using the developed model, the optimization design of the main transmission of a fruit/vegetable washer was carried out. The genetic algorithm optimization has yielded 73 Pareto optimal solutions, and the three most suitable solutions according to the specific manufacturing capability were determined by employing a decision-making process based on the method of successive concessions. Further, a comparative study showed that the solutions obtained by the developed model have excelled the one obtained by means of the experience-based approach. It is noteworthy that the generalized mathematical model and the problem-solving approach adopted in this work can also be used for the SCM synthesis of other mechanical systems.

Investigation on very high cycle fatigue of PA66-GF30 GFRP based on fiber orientation

The purpose of this study is to evaluate the effects of glass fiber (GF) of PA66-GF30 orientation on very high cycle fatigue (HVCF) life and also to develop an optimized test apparatus such as measurement of dynamic elastic modulus and design of test specimens. Dynamic elastic modulus, tensile strength and fatigue strength tests were conducted at room temperature based on GF orientation (0°, 45°, 90°). Conventional fatigue (3 Hz) and ultrasonic fatigue (20 kHz) tests were performed at the same stress ratio (R = −1). Fracture surface observation showed that GF 0° exhibited a higher fatigue strength in comparison with GF 45 and 90°. Various defects such as voids and microcracks to the load direction around the GF end or debonding in glass fiber reinforced plastic (GFRP) and the slope change in very long life regime of S–N diagram.

Theoretical approach to determine dynamic fatigue strength characteristics of ceramics under variable loading rates on the basis of SCG concept

This paper presents a theoretical approach to determine the dynamic fatigue strength characteristics of ceramics under variable loading rates on the basis of the slow crack growth (SCG) concept. First, a probabilistic effective inert strength model was derived on the basis of the SCG concept in conjunction with the Weibull distribution for ceramics subjected to multi-stage loading. Second, a four-point bending test was conducted on $$\hbox {Al}_{{2}}\hbox {O}_{{3}}$$ under constant and two-stage variable loading rates, and the fracture surface was then observed. The experimental data that depend on loading rates can be unifiedly evaluated after converting the data to the effective inert strength, obeying the three-parameter Weibull distribution. In addition, the Weibull plots of the inert strength, which were calculated from the inclusion size on the fracture surface using the grain fracture model, showed good agreement with the three-parameter Weibull distribution for the converted effective inert strength. These analytical results theoretically indicate that dynamic fatigue under variable loading rates occurs by obeying SCG at the inclusion. Further, the inert strength and its scatter depend on the size and distribution of inclusions.

Identification of dynamic loads applied to an elastically deformed element of constructions

The technique has been presented for time-dependence identification of several independent beetwen each other loads distributed over a given area of a structure with arbitrary topology by using quantity values more convenient for measurements. In the assumption that the structure’s response linearly depends on the loads, the considered problem, which belongs to the class of boundary inverse problems in the mechanics of solids, is reduced to a system of linear algebraic equations for coefficients that approximate the sought-for influences. The system is solved using a regularizing algorithm providing stability of results to random errors in initial data and calculation errors. Concrete calculations, substantiating the efficiency of the presented technique, have been performed as with theoretical data to identify two non-stationary loads applied to a wheel carrier of a race car as with experimental data to restore an impact force applied to a round plate with fixed boundary. To calculate values of a system’s elements corresponding to values of measured quantities under unit loads, the finite element method was used. The suggested technique can be used for designing structures with complex geometry based on criterias of their dynamic (fatigue) strength, etc.

Fatigue behavior of zirconia under different loading conditions

PurposeTo investigate the influence of surface damage on the fatigue behavior of zirconia under two different loading conditions. Materials and methodsOne hundred twenty zirconia bar-shaped received either airborne particle abrasion using 50μm or 120μm alumina particles while polished specimens served as control. The specimens were subjected to two fatigue regimes: dynamic fatigue (1,000,000 cycles, 1hz and 0.5s contact time) or static fatigue (a constant load applied for 5000s) under water using the staircase application of the load. The flexure strength after fatigue (dynamic fatigue strength) was compared to the initial flexure strength of the tested specimens (α=0.05). The critical crack shape and size of fractured specimens was examined using scanning electron microscopy. ResultsCompared to the initial flexure strength of the tested specimens, dynamic fatigue strength was 86.3% for the polished specimens, 73.4% for 50μm particle abrasion, and 42.3% for 120μm particle abrasion while the static fatigue strength was 85.9%, 78.5%, and 51.5% respectively. Significant statistical differences (F=223.679, P<0.001) were found between different surface treatments but not between dynamic and static fatigue strengths for the same type of surface treatment. ConclusionsThe dynamic and static fatigue strengths of zirconia are significantly influenced by type of surface damage. Clinical ImplicationsWithin the limitations of this study, surface damage have great influence on fatigue behavior of zirconia.

Crankshaft Design Optimization to Improve Dynamic Balancing and Fatigue Strength

Crankshaft Design Optimization to Improve Dynamic Balancing and Fatigue Strength

Time-dependent fracture probability of bilayer, lithium-disilicate-based, glass–ceramic, molar crowns as a function of core/veneer thickness ratio and load orientation

Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure. ObjectiveThe aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6mm reduces the time-dependent fracture probability (Pf) of bilayer crowns with a lithium-disilicate-based glass–ceramic core, and (2) oblique loading, within the central fossa, increases Pf for 1.6-mm-thick crowns compared with vertical loading. Materials and methodsTime-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass–ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass–ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic). ResultsPredicted fracture probabilities (Pf) for centrally loaded 1.6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8mm/0.8mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4mm/1.2mm). ConclusionCARES/Life results support the proposed crown design and load orientation hypotheses. SignificanceThe application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures.

레이저 용접된 박판 지르코늄 합금의 피로특성

The spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water and maintains geometry from external impact load and cyclic stress by the vibration of nuclear fuel rod, it is necessary to have sufficient strength against dynamic external load and fatigue strength. In this study, the mechanical properties and fatigue characteristics of laser beam welded zircaloy thin sheet are examined. The material used in this study is a zirconium alloy with 0.66 mm of thickness. The fatigue strength under cyclic load was evaluated at stress ratio R

FATIGUE CHARACTERISTICS OF LASER WELDED ZIRCALOY THIN SHEET

The spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water and maintains geometry from external impact load and cyclic stress by the vibration of nuclear fuel rod, it is necessary to have sufficient strength against dynamic external load and fatigue strength. In this study, the mechanical properties and fatigue characteristics of laser beam welded zircaloy thin sheet are examined. The fatigue strength under cyclic load was evaluated by staircase method at stress ratio R =0.1. The most appropriate distribution for probabilistic characteristics of fatigue strength at 2×106 cycles was 2-paramer Weibull distribution. Results show that reliability analysis strength was derived from the strength-stress interference model. As a result of the experimental approach, the design guide of fatigue strength for laser welded joint is proposed and the results obtained in this are to be the useful data for spacer gird design.

Dynamic Fatigue Simulation of Engine Block Based on Virtual Prototype Technology

This paper carried out simulation analysis on the dynamic fatigue strength of an inline six-cylinder engine block based on the measured indicator diagram by the means of virtual prototype technology. A 3D solid model of the crankshaft block system is established firstly. After that, based on finite element method, dynamic stress of the block under operating conditions is obtained, by the means of Multi-body dynamics method. Then, calculation analysis on the fatigue safety coefficient of the engine block is made.

Estimation of dynamic fatigue strengths in brittle materials under a wide range of stress rates

This paper aims to statistically estimate the dynamic fatigue strength in brittle materials under a wide range of stress rates. First, two probabilistic models were derived on the basis of the slow crack growth (SCG) concept in conjunction with two-parameter Weibull distribution. The first model, Model I, is a conventional probabilistic delayed-fracture model based on a concept wherein the length of the critical crack growth due to SCG is enough larger than the initial crack length. For the second model, Model II, a new probabilistic model is derived on the basis of a concept wherein the critical cracks have widely ranging lengths. Next, a four-point bending test using a wide range of stress rates was performed for soda glass and alumina ceramics. We constructed fracture probability–strength–time diagrams (F–S–T diagrams) with the experimental results of both materials using both models. The F–S–T diagrams described using Model II were in good agreement with plots of the fracture strength and the fracture time of both materials more so than Model I.

Research on Dynamic Fatigue Strength Criterion of BTA Deep Hole Boring Bar for Consideration Vortex Surrounded by Internal and External Cutting Fluid

Fatigue failure is the most common failure mode of boring bar in the deep-hole boring processing system. For solving the problem of fatigue failure on boring bar, the new fatigue strength criterion of boring bar is proposed considering the working state including internal and external cutting fluid vortex, linear crack of the across-section, and the maximum bending - torsion coupled stress of boring bar. Firstly, approximate calculation formula of the maximum bending stress was derived considering internal and external cutting fluid coupled effect induced vortex motion. Secondly, near the region of crack tip, the maximum shearing stress was studied when the failure modes of boring bar was considered to linear crack on its cross-section. Finally, the new fatigue strength criterion was established based on bending-torsion combination alternating stress fatigue strength theory. An example calculation in practice showed that if fatigue strength of boring bar is satisfied to the new fatigue strength criterion, its static strength must be satisfied. The new fatigue strength criterion can be used in analyzing the boring bar’s fatigue strength on both complicated working conditions and also single working conditions. The mechanism of failure and destruction of boring bar on BTA deep hole drilling in generally actual working conditions were studied in this paper which are helpful to promote the service life cycle of boring bar in practice. Some rules are also derived to assess the dynamic performance of working boring bar, which structure parameters will be selected reasonably according to it.

S042022 変動負荷速度下におけるセラミックスの動的疲労強度分布特性と破壊メカニズム([S04202]セラミックスおよびセラミックス系複合材料(2))

This paper presents probabilistic approach for estimating the dynamic fatigue strength inceramics under variable stress rate. First, a probabilistic model was proposed on the basis of the slow crack growth concept in conjunction with two-parameter Weibull distribution. Second, the four-point bending test was carried out for alumina ceramics under two-step stress rate at room temperature. The experiment result was compared with the predictions to verify the validity of the model. The fracture surface of the specimen after the bending test was also observed. It is seen that mirror, mist and hackle in the vicinity of the surface acting maximum stress. Therefore, the dynamic fatigue fractures under variable stress rate caused by slow crack growth from an initial crack. We constructed fracture probability - bending strength diagrams (F-S diagrams) with the experimental results using the model. The F-S diagrams were in good agreement with Weibull plots of the bending strength.

Dynamic Response and Fatigue Strength of Depressed Center Flat Frame

Based on finite element method and multi-body system dynamics theory,the dynamic response of depressed center flat car multi-body system,the fatigue life and elastic vibration of its depressed center flat underframe are studied.After the wheel-rail contact,track spectrum and vehicle nonlinear factors being calculated and simulated,the dynamic equations of depressed center flat underframe are established by using super-element method based on finite element analysis software ANSYS.The finite element analysis results are introduced into the dynamics software SIMPACK,and the multi-rigid-body system and rigid-flexible coupling system dynamics models of the depressed center flat car are established.Simulation calculation is carried out,then compared with the test result to study the effects of running speed and suspension parameter on the dynamic response of vehicle system.The dynamic clearance and fatigue strength of depressed center flat underframe are also analyzed.The results show that the rigid-flexible coupling model is more reasonable.The running speed of the loaded car should not be too high,and suspension parameters should be properly matched.

Calculation of Dynamic Stress and Fatigue Strength of Crankshaft with Bush Deformation Included

Dynamic stress and fatigue strength of a crankshaft of diesel engine with four cylinders is studied with consideration of the elastic deformation of bush. Special software ADAMS and ANSYS, assisted by self-designed programs, are adopted to solve the problem. The dynamic pressures of oil film in the bearings are obtained by analysis of dynamics and tribology of the crankshaft-bearing system with consideration of bush deformation. Programming language APDL in ANSYS is adopted to compile program for realizing the force boundary condition, then the dynamic stress on crankshaft journal surfaces is calculated. The fatigue strength of crankshaft is calculated by using damage accumulation theory. It is shown that the minimum thickness of oil film decreases and the maximum pressure of oil film increases to a great extent if the elastic deformation of bush is taken into consideration. The dynamic response and stress of crankshaft vary and the fatigue life of crankshaft decreases by 15.6%.

How long can single-walled carbon nanotube ropes last under static or dynamic fatigue?

We report a study on the static and dynamic fatigue behavior of unidirectional, aligned single-walled carbon nanotube (SWCNT) ropes. By bench marking against the behavior of graphite fiber, it is found that the static fatigue strength of SWCNT ropes is at least twice that of graphite fiber within 104s and is similar to that of graphite fiber at longer times, while the dynamic fatigue strength is twice that of the graphite fiber to up to 107cycles. Fatigue limit seems to exist for SWCNT ropes within the time scale of the investigation at 4–5GPa. Based on experimental data and results of a molecular life prediction scheme, it is suggested that the fatigue behavior of SWCNT ropes may be controlled by preexisting defects.

Fatigue properties of intact sandstone samples subjected to dynamic uniaxial cyclical loading

In this paper, the fatigue behaviour of intact sandstone samples obtained from a rockburst prone coal mine and studied under dynamic uniaxial cyclic loading in the laboratory is presented. Tests were conducted on dry and saturated samples with loading frequencies ranging from 0.1, 1 and 10 Hz and amplitudes of 0.05, 0.1 and 0.15 mm. From the laboratory investigations, it was found that the loading frequency, as well as the amplitude, was of great significance and influenced the rock behaviour in dynamic cyclic loading conditions. The dynamic fatigue strength and the dynamic axial stiffness of the rock reduced with loading frequencies and amplitude. The dynamic modulus was found to increase with the loading frequency but decrease with the amplitude. In the case of the saturated samples, it was found that the dynamic fatigue strength reduced by approximately 30 per cent, while the dynamic Young's modulus reduced by about 20 per cent. From the presented study, the dynamic energy was found to be independent of the testing conditions while other rock properties were found to be dependent on these. Finally, it was concluded that rock would more readily succumb at low frequencies and amplitude than at high frequencies and amplitude for a given energy availability.

Dynamic fatigue of a Si 3N 4+SiC nanocomposite at 1350°C

The dynamic fatigue strength of a hot pressed silicon nitride/silicon carbide nanocomposite and reference monolithic Si 3N 4 have been investigated in four-point bending at 1350°C in air using different loading rates from 0.01 to 1 mm min −1. The flexure strength significantly decreased with decreasing stress rate in both ceramics, however at all stress rates the strength of the composite was lower than that of the monolithic. The formation and growth of a stress-oxidation damage zone are primarily responsible for the strength degradation of the monolithic ceramic. In the composite intrinsic flaws were the main fracture origins, which extend by oxidation assisted slow crack growth and decrease the strength of the specimens significantly.

Fatigue Strength as a Function of Preloading in Dynamic Fatigue Testing of Glass and Ceramics

The solution of fatigue strength as a function of preloading in dynamic fatigue (constant stress-rate) testing was obtained analytically and numerically. The effect of preloading on dynamic fatigue strength decreases with increasing fatigue parameter (n), and for n ≥ 20 the effect is negligible up to a preloading of 90 percent. The solution was verified by dynamic fatigue experiments conducted with soda-lime glass and alumina specimens in room-temperature distilled water. This result showed that one can apply a preloading corresponding up to 90 percent of fatigue strength for most glass and ceramic materials, resulting in a dramatic saving of testing time in dynamic fatigue testing. The key feature that makes this technique feasible is that most of the slow crack growth under dynamic fatigue loading occurs close to failure time where the dynamic fatigue strength is defined.

Preloading Technique in Dynamic Fatigue Testing of Glass and Ceramics with an Indentation Flaw System

The solution of fatigue strength as a function of preloading in dynamic fatigue testing was obtained numerically for an indentation flaw system. The dynamic fatigue strength is dependent on preloading and fatigue parameter (K). The effect of preloading on dynamic fatigue strength decreases with increasing fatigue parameter: for n 20 the effect is negligible up to a preloading of 90%. The solution was verified by dynamic fatigue experiments conducted with soda‐lime glass and alumina specimens with as‐indented flaws in room‐temperature distilled water. The result indicates that one can apply a preloading corresponding up to 90% of fatigue strength for most glass and ceramic materials with no change in fatigue strength, resulting in a dramatic saving of testing time.