Design Of Mechanical Components Research Articles

Fatigue life prediction: A comparative study for a three layer EN45A parabolic leaf spring

Article history: Received 6 January, 2015 Accepted 10 May 2015 Available online 12 May 2015 There are literally several studies accomplished to predict the fatigue life of leaf springs but estimation of fatigue life of a parabolic leaf spring by using CAE tools has not yet been executed in the past. Parabolic spring is an important component in a vehicle suspension system. It needs to have excellent fatigue life and in today’s scenario manufacturers rely on constant loading fatigue analysis. The objective of this work is to perform the fatigue analysis of parabolic leaf spring by three different methods where CAE analysis is performed to observe the distribution of stress fatigue life and damage using Goodman approach. In this work, fatigue life of the parabolic leaf spring is determined as per SAE spring design manual and experimentally by testing on full scale fatigue testing machine. ANSYS is used for CAE solution for the prediction of leaf springs fatigue life considering stress theory. The fatigue life estimated by all three modes is then compared for the purpose of validation. The methodology used in this paper brings a practical approach to the professionals in the industries who are engaged for design of mechanical components. © 2015 Growing Science Ltd. All rights reserved.

A probabilistic interpretation of the Miner number for fatigue life prediction

The Miner number M, used as a tool for lifetime prediction of mechanical and structural components in most of the standards related to fatigue design, is generally accepted as representing a damage stage resulting from a linear progression of damage accumulation. Nonetheless, the fatigue and damage approach proposed by Castillo and Fernández-Canteli, permits us to reject this conventional cliché by relating M to the normalized variable V, which represents percentile curves in the S-N field unequivocally associated to probability of failure. This approach, allowing a probabilistic interpretation of the Miner rule, can be applied to fatigue design of mechanical and structural components subjected to variable amplitude loading. The results of an extensive test program on concrete specimens under compressive constant and load spectra, carried out elsewhere, are used. A parallel calculation of the normalized variable V and the Miner number M is performed throughout the damage progression due to loading allowing probabilities of failure to be assigned to any value of the current Miner number. It is found that significant probabilities of failure, say P=0.05, are attained for even low values of M, thus evidencing the necessity of a new definition of the safety coefficient of structural or machine components when the Miner rule is considered. The experimental and analytical probability distributions of the resulting Miner numbers are compared and discussed, the latter still providing a nonconservative prediction in spite of the enhancement. A possible correction is analyzed.

The WEST project mechanical analysis of the divertor structure according to the nuclear construction code

The Tore Supra tokamak is being transformed in an x-point divertor fusion device in the frame of the WEST project, launched in support to the ITER tungsten divertor strategy. The installation of coils inside the vacuum vessel led to the design of a divertor supporting platform able to meet the project requirements and the associated electromagnetic loads. This paper illustrates the design, the method and the results of the thermomechanical elastic stress analyses performed in 2012. The validation of the integrity of the structure is based on the compliance with RCCMR design criteria (even though these Design and Construction rules for Mechanical Components of nuclear installations are not required for such experimental fusion device).Several 3D analyses are performed with the ANSYS code. The major one is a global analysis of half structure which determinates the stresses in the main part of the components. It gives an idea of the areas which needs local analyses. It also provides the interface loads for junction studies or simplified local model.

Free Form Shape of Machine Parts Design Based on Microcomputer CAD/CAM System

CAD/CAM system is one of the most widely used software in the field of mechanical design and manufacturing. The design of the mechanical parts generally uses CAD/CAM software, such as SolidWorks, Unigraphic, Pro/Engineer etc.. In this paper, by using UG software as a development platform, we use the software of UG/OPEN GRIP and UG MACRO as secondary development tool to realize the customization and development of general model of CAD/CAM system, and apply it in the design of professional free format machine parts. In the CAD/CAM system we put free format into parts manufacturing process and technology, and put forward the simple and effective process flow, so as to realize the optimization of CAD/CAM system. It provides the technical reference for the design and process of mechanical components.

Comparative analysis of tooth-root strength using stress–strength interference (SSI) theory with FEM-based verification

Gear geometry plays a significant role in deciding the tooth deflection, magnitude of stress induced and stress distribution. Accurate evaluation of the stress state and distribution of stresses at the tooth root requires application of experimental methods to determine, such as electric resistance wire strain gauges, or photoelastic gauges, etc. These experimental methods are especially complicated, expensive, and laborious. Therefore, they are applied mainly in special cases. In the recent years, the methods of probabilistic design have been commonly accepted in the design of mechanical components and systems to assist the designer in making decisions on the best balanced design with respect to several design criteria. In probabilistic design, it is common to use parametric statistical models to calculate the probability of failure obtained from the Stress–Strength Interference (SSI) theory, which more nearly models the true situation. This paper discusses the application of the SSI theory that has been used to support the detailed gear design as part of the “Design for Reliability” approach to evaluate the tooth-root strength with finite element method-based verification. The SSI theory is formulated to predict the effect of the root fillet generated by rack or hob tool with and without protuberance on the gear system reliability. The results indicate the high fillet root stresses and gear tooth deflection in gears with the lowest tip radius of the generating tool.

Influence of Errors in Young’s Modulus on Fatigue Life Predictions of Notched Round Bars Under Bending-Torsion Loading

Elastic constants are fundamental to characterise the stress-strain behaviour of materials which is essential for an accurate design of mechanical components against fatigue failure. In this paper, the first objective is to address recent patents on the determination of elastic constants and on fatigue life prediction methods. The second objective aims at studying the effect of errors in elastic constants on fatigue life prediction. Elastic constants are determined using dynamic and static methods, namely the Impulse Excitation Technique (IET) and the Three-Point Bending Test (3PBT). Then, high-cycle fatigue tests in notched round bars subjected to different bending-torsion loading scenarios are conducted to obtain experimental fatigue lives. Finally, experimental fatigue lives are compared with fatigue life predictions obtained for the different Young's moduli obtained previously. Results demonstrated that predictions based on the IET are more accurate than those obtained from the 3PBT. Recent patents on the determination of elastic constants and on fatigue life prediction methods are also addressed.

W042002 フレッティング疲労に及ぼす水素の影響([W04100]機械材料・材料加工部門企画,締結・接合のプロセスと接合部・界面の信頼性評価)

Fretting fatigue, which is a composite phenomenon of metal fatigue and friction, is one of the major factors in the design of mechanical components. Since hydrogen can influence both fatigue and friction, importance of fretting fatigue is highlighted in hydrogen equipment. The fretting fatigue strength of austenitic stainless steels significantly reduced by the effects of hydrogen. One of the major reasons for the reduced fretting fatigue strength in hydrogen gas is adhesion between contacting surfaces. Friction force is transmitted through the small area of the adhered spots, severe stress concentration then arises in the vicinity of the adhered spots. This increase in mechanical stress assists crack initiation. Furthermore, evidences of severe cyclic plastic deformation is found at the adhered part. The plastic deformation results microstructure change. These are other important factors for the reduction in fatigue strength due to hydrogen, because plastic deformation is essential for the functions of hydrogen regarding HELP mechanism, hydrogen diffusion and hydrogen concentration. Fretting fatigue test of hydrogen charged materials are also carried out. Internal hydrogen also reduced critical stress to crack initiation, and it resulted reduction in the fretting fatigue strength.

ProFatigue: A Software Program for Probabilistic Assessment of Experimental Fatigue Data Sets

In this work, the software program ProFatigue is presented as a practical tool for derivation of probabilistic S-N and ɛ-N fields from experimental fatigue data. The program provides an estimation of the parameters involved in the regression probabilistic Weibull fatigue model developed by the authors, allowing an advantageous application of both fields to the stress or strain based approaches in the fatigue design of structures and mechanical components. An extension to the analysis of more complex and varied lifetime problems as thermomechanical, multiaxial and fretting fatigue is possible by adopting suitable damage parameters proposed in the literature as driving force. Application to probabilistic assessment of cumulative damage and further program enhancement are now envisaged.

230°C Accelerometer with Digitized Output for Directional Drilling

Measurement-While-Drilling (MWD) technology for oil and gas, and geothermal directional drilling exploration is pushing into ever higher temperature environments - beyond 200°C. Orientation sensors supporting these high temperature environments need to provide highly accurate elevation and tool face measurements on the order of 0.1°. Honeywell has developed a new digital high temperature down-hole accelerometer, DHTA230, capable of providing the required accuracy at the elevated temperatures of 230°C, in the rugged MWD shock and vibration environment, with expected excellent reliability and life. The DHTA230 is designed for use in the downhole environment, but is based upon a mature Honeywell accelerometer using dual vibrating beam sensing elements. These sensing elements are configured as double-ended-tuning-forks in a push-pull orientation attached onto a pendulous proof mass. This push-pull configuration provides an acceleration signal proportional to the frequency difference of the vibrating beams, an easily captured digital signal through measurement of the two vibrating beam phases. The digitized accelerometer eliminates the need for A/D electronics in the high temperature drilling environment. The DHTA230 is 0.79” in diameter with a depth of .393” at the mount flange. The ruggedized configuration of the DHTA230 is expected to provide reliable orientation measurement in high temperature direction drilling applications up to 1000h. The DHTA230 electronics incorporate ceramic hybrids with chip and wire construction. Active die are based upon proven 300°C chips developed previously for the Enhanced Geothermal Systems OM300, fabricated using Honeywell HTSOI4 process. The electronics include power conditioning providing reliable operation using a single power supply between 7V and 15V. Dual oscillator electronic circuits provide the necessary function to drive and sense the dual vibrating beams, while providing a CMOS logic level signal of the frequency pulse train. The accelerometer provides precision output up to 15g acceleration inputs, and allows sensing of higher-g vibration levels. This paper contains information on the target application, electrical and mechanical component requirements, design, fabrication approach, and initial prototype testing. The DHTA230 is expected to enter production transition in 2015.

Reliability-Based Robust Design of Mechanical Components with Correlated Failure Modes Based on Moment Method

There are usually several potential failure modes in mechanical components. The conventional model for the system analysis is built under the condition that all failure modes are independent of each other. However, in engineering practice, failure modes are mostly dependent due to the fact that the elements involved in each failure mode are closely interrelated. System reliability analysis and evaluation simply conducted under independent assumption often result in excessive errors or even wrong conclusion. A novel method to evaluate system reliability of mechanical components with multiple failure modes based on moment method are proposed here. Firstly, the moment-based reliability and reliability sensitivity analysis method is proposed with independent assumption. Secondly, the proposed method is deduced by taking the correlation between failure modes into account and the correlation model is established with the copula function, which is proved to be a useful tool to model nonlinear correlation with marginal distributions. The robust design is performed as a biobjection optimization process based on the reliability sensitivity. The numerical examples show that the applied procedure is able to efficiently consider various failure modes of mechanical components in probabilistic assessment and reliability-based optimization.

Fatigue Threshold R‐curves Predict Fatigue Endurance Strength for Self‐Reinforced Silicon Nitride

There is a need for methods that can help predict and avoid fatigue failures of silicon nitride ceramic components. The fatigue threshold R‐curve has been proposed as potential solution to this problem. In this study, the fatigue threshold R‐curve for small, semielliptical surface cracks was calculated for a silicon nitride ceramic using the published bridging stress distribution developed from fatigue threshold tests on macroscopic crack specimens. To test the accuracy of the endurance strengths predicted using the fatigue threshold R‐curve, fatigue tests were conducted using four‐point bend beams of silicon nitride containing semielliptical surface cracks introduced by Knoop indentation. The effectiveness of the methodology was verified; indeed, 77% of the beams tested at stress levels above the predicted endurance strength failed within 107 cycles and 0% of the beams tested below the predicted endurance strength failed within 107 cycles. Furthermore, using the bridging stress distribution, which is thought to be a material property, the need for prohibitively difficult fatigue threshold experiments on small surface cracks is avoided. Accordingly, this methodology is potentially quite practical for use in the engineering design of ceramic mechanical components.

A mechanical structure-based design method and its implementation on a fly-cutting machine tool design

The mechanical structure has a main influence of the machining performance and the servo performance. In this study, a mechanical structure-based design method is presented to design and optimize an ultraprecision fly-cutting machine tool. This method takes full account of the influence of mechanical components on the machining performance and servo performance at the design stage. The effect of the components structure on the roughness of machined surface is discussed, and an optimized structural form of the aerostatic spindle is given. The influence of the mechanical structure on the control system and electronic drives is discussed, and an integrated dynamic design model is built and used to optimize the hydrostatic slide. Furthermore, the impact of mechanical system dynamic performance of the machine tool on the processing topography is analyzed by the finite element model of the machine tool. This method provides a theoretical basis for the design and optimization of mechanical components and machine tools stiffness loop.

Mechanical Components Design and Research Based on Reliability

In this paper, the reliability design method was used during the process of mechanical parts designing, the design parameters was regarded as random variables, the reliability index of products was involved in the design of the entire process, making the design more in line with the results of the actual situation. The general process of the reliability design was explained by the design of typical part. A good method to effectively improve product quality, reduce part size, save materials and reduce the cost was founded, and the same time the method can make the design of the products more competitive in the market.

Reliability Model for Complex Mechanical Component Design

Taking into account the uncertainty in material property and component quality, a complex mechanical component such as a gear should be treated as a series system instead of a component when evaluating its reliability, since there exist many sites of equal likelihood to fail. Besides, conventional system reliability model is not applicable to such a system because of the statistical dependence among the failures of the every element (damage site). The present paper presents a model to estimate complex mechanical component reliability by incorporating order statistic of element strength into load-strength interference analysis, which can deal with multiple failure mechanisms, reflect statistical dependence among element failure events and that among different failure modes.

Gradual Change Reliability Sensitivity Design for Tool Based on Measured Information

It brings certain error to reliability design of mechanical components that now most reliability design aiming at establishing pure theoretical mathematical model, without considering arbitrary distribution and variation rules of parameters. In this paper, the variation rules of strength and load effect are studied, the computational method of gradual change reliability is given. By combining the theory of reliability design with the method of sensitivity analysis, the restrictions on random variable distribution types are loosen, the gradual change reliability sensitivity design method with arbitrary distribution parameter is proposed based on the measurement information. Under the circumstance that knowing the first four order moments of basic random parameter, reliability sensitivity design with arbitrary distribution parameter can be brought about by using computer program, which provides the theoretical basis for structural design and life forecast of mechanical components.

A STEP-NC compliant system for the remote design and manufacture of mechanical components through the Internet

The rapid advances of information and manufacturing technologies have caused significant changes to the manufacturing environments in recent decades. The Internet has introduced e-manufacturing (i.e. designed by anyone anywhere, manufactured by anyone anywhere). The key to the success of e-manufacturing consists of a compatible data stream with no gaps in the CAD-CAPP-CAM-CNC chain. Despite advances in manufacturing technologies, the language used in numerical control machines today (i.e. G-code – ISO 6983 standard) is still based on the movements of the cutting tools and the status of the machine, causing the loss of a lot of information about the product, making it difficult or impossible to share such information with different areas of the company. Given this context, this paper presents a CAD/CAPP/CAM prototype system for the remote manufacturing of mechanical components using the Internet as a means of communication, being completely compliant with ISO 14649 (STEP-NC). One of the modules of the system checks whether the component created by the user is valid from the standpoint of manufacturability with the cutting tools available. In addition, the system identifies whether the component can be manufactured in a three axes numerical control machine. Finally, the system automatically generates the STEP physical file format (ISO 10303 part 21), which is enabled to the user via the Internet, and he/she can perform a graphic simulation of the movement of the tools machining the component, using the physical file.

Reliability-Based Robust Design for Mechanical Components under Small-Sample Information

In engineering design, according to not considering past experience information; hence, to make structure parameters for achieving high confidence level, much data for traditional reliability-based robust design must be adequately collected, analyzed, and tested. However, in practical engineering, it is very difficult for doing much test, only for getting in the form of finite test samples. Under the conditions, it has much difficult for the traditional reliability-based robust design. In the article, we present a new reliability-based robust design method that solves the form of incomplete information. The method adopts a Bayesian inference technique to estimate reliability, gives definition of Bayesian reliability. In the research, the mechanical parts bayesian reliability-based robust design mathematical model is established and the bayesian reliability-based robust design approach is presented. The numerical results illustrates the method presented is an efficient and practical reliability-based robust design approach.

Reliability Optimization Design for Mechanical Components

The traditional reliability model of mechanical components can not well reflect the effect of strength degradation on reliability。In the paper, A new method is applied to develop a dynamic reliability model of mechanical components considering the strength deterioration with time passing。The calculated result s by a real example show that could not only calculate the failure probability of the response, but also could make the process of optimization of the response under the conditions of meeting reliability restraint.

Reliability assessment of hydraulic cylinders considering service loads and flaw distribution

Manufacturing process, service conditions and material properties are all necessary requirements to a good design of tubular mechanical components subjected to fatigue. The most common approach to this design is usually deterministic, where a fixed NDT threshold, related to flaw acceptance limit, is set. However many uncertainties are left aside, i.e. the failure probability related to the fatigue strength under applied loads.This paper addresses the reliability evaluation of tubular mechanical components carrying some flaws and subjected to cyclic internal pressure variation. The aim is comparing the probability of failure obtained under several assumptions.A reliability assessment model, based on a random variable approach, has been implemented by using the Monte Carlo method.The analysis of the results, from a case study based on load spectra measurements of hydraulic cylinders of earth moving machines, has consented to evaluate the most important factors influencing the fatigue life prediction of these components.

Research on Mechanical Performance Analysis and Structural Modification of Longitudinal Thrust Rod

To research the mechanical performance and vibration modes of current longitudinal thrust rod of rear axle, the finite element model of original thrust rod is established and analyzed with NASTRAN codes. The simulation results demonstrate: the maximum stress of original thrust rod of dump truck is in the limit of the yield strength of material, which satisfies with the design requirements; the first step modal frequency of the component under free conditions is greater than upper limits value of the excited frequency of roads, which can evade the resonance excited by irregular roads. But there is structural stress concentration area in the thrust rod, so the structure of thrust rod is modified to ameliorate the stress state of this area. The maximum structural stress is reduced by 35.1% on the basis of reduction by 4.7% in total weight, which indicates the modification improves the mechanical and modal performance greatly. The research above has significant reference values for mechanical performance analysis and lightweight design of complicated automotive components.