Design evaluation of a French refrigerator drawer system subjected to repeated food storage loads

Based on field data and a tailored set of accelerated life tests, the drawer system of food storage in a French refrigerator was redesigned. Using a force balance analysis, the simple mechanical loads of the drawer system were evaluated. The failure modes and mechanisms found experimentally were similar to those of the failed samples in the field. Failure analysis, accelerated life tests and corrective action plans were used to identify the key control parameters and level for the mechanical drawer system. The missing controllable design parameters of the drawer system in the design phase included no corner rounding and rib thickness in the intersection areas between the box and its cover, the right, center support and left rail system. After a tailored series of accelerated life tests with corrective action plans, the B₁ life of the new draw system is now guaranteed to be over 10 years with a yearly failure rate of 0.1%.     

Reliability design and case study of refrigerator parts subjected to repetitive loads under consumer usage conditions

When newly designed refrigerator parts failed due to repetitive loads under consumer usage conditions in the field, a general method for reliability design was proposed. A newly designed refrigerator compressor system that brings greater energy efficiency to side-by-side (SBS) refrigerators was studied. The laboratory failure mode and mechanism of the compressor was a stopping nose due to design flaws. The data on the failed products in the field, accelerated life tests (ALT) and corrective action plans were used to identify the key control parameters for the mechanical compressor system. The missing controllable design parameters of the compressor system in the design phase were the gap between the frame and the upper due to the stator frame shape. After a tailored series of accelerated life tests with corrective action plans, the B₁ life of the new compressor system is now guaranteed to be over 10 years with a yearly failure rate of 0.1%.     

A Bayesian Approach to Multiple Comparisons

This paper presents maximum likelihood theory for large-sample optimum accelerated life test plans. The plans are used to estimate a simple linear relationship between (transformed) stress and product life, which has a Weibull or smallest extreme value distribution. Censored data are to be analyzed before all test units fail. The plans show that all test units need not run to failure and that more units should be tested at low test stresses than at high ones. The plans are illustrated with a voltage-accelerated life test of an electrical insulating fluid.     

Measurement Uncertainty: Methods and Applications

We consider the problem of determining an optimal experimental design for estimation of parameters of a class of complex curves characterizing nanowire growth that is partially exponential and partially linear. Locally D-optimal designs for some of the models belonging to this class are obtained by using a geometric approach. Further, a Bayesian sequential algorithm is proposed for obtaining D-optimal designs for models with a closed-form solution, and for obtaining efficient designs in situations where theoretical results cannot be obtained. The advantages of the proposed algorithm over traditional approaches adopted in recently reported nanoexperiments are demonstrated using Monte Carlo simulations. The computer code implementing the sequential algorithm is available as supplementary materials.     

船体水上防锈漆体系加速试验方法研究

根据船舶水线漆和船壳漆的使用环境和主要破坏因素，设计了一套以盐雾－人工加速老化（紫外光／冷凝）交替暴露和带人造缺陷样板的加速暴露试验方法为主，结合海水冲刷、附着力等主要力学性能测定的试验方案。对８种国内外船体水上部份防锈漆体系的性能进行综合评定，其结果采用数字量化评分。试验结果表明，该试验方法可在相当短的时间内对各类船体水上防锈漆体系的综合性能作出正确的评定。     

The Constant Shape Parameter Assumption in Weibull Regression

ABSTRACT

The usual assumption in Weibull regression is that the scale parameter is a function of the predictor variables, and the shape parameter is constant. We consider the problem of estimating parameters in the presence of a nonconstant shape parameter and the effect of assuming a constant shape parameter when it really is not constant. We consider both classical and Bayesian methods of estimation. The misspecification of a constant shape parameter can lead to a loss of power for tests regarding the slope parameters. We find that prediction intervals can be inaccurate when the shape parameter is incorrectly assumed to be constant.     

A stress approach model for predictions of fatigue life by shot peening of EN45A spring steel

A lot of research has been done to improve fatigue strength of materials by creating compressive residual stress field in their surface layers through shot peening. In this paper, fatigue strength of shot peened leaf springs has been calculated from laboratory samples. The axial fatigue strength of EN45A spring steel specimen is evaluated experimentally as a function of shot peening in the conditions used for full-scale leaf springs testing in industries. Optimum shot peening condition for specimen is found and S/N curves of the specimens are correlated with leaf springs curve. A mathematical model has been developed which predicts the fatigue life of leaf springs for a given stress at varying shot peening conditions. Predictions from this model are compared with experimental data. The estimation of fatigue life and relaxation of compressive residual stress field are discussed.     

Experiment and modeling of uniaxial tension fatigue performances for filled natural rubbers

A tension fatigue model of filled natural rubbers is investigated to study the contributions of two key factors, namely, the damage parameter and the specimen geometry used in the fatigue experiment. The uniaxial tension fatigue experiments were carried out for three filled natural rubber specimens with different geometry: a dumbbell simple tension specimen (STS), a dumbbell cylindrical specimen (DCS), and a hollow cylindrical specimen (HCS). The commonly used damage parameters for fatigue life prediction are discussed. The fatigue life prediction models are formulated using the measured tension fatigue life of the STS together with different damage parameters. The effectiveness of the models is established in terms of a correlation coefficient characterizing the error between the measured and predicted fatigue lives. It is concluded that all the damage parameters considered in the study can effectively estimate the tension fatigue life with correlation coefficients exceeding 0.9. The fatigue life model formulated for the STS was also found to be appropriate for predicting the fatigue life of specimens with different geometry (DCS and HCS) suggesting that the relationship between the tension fatigue life and the damage parameters is independent of the specimen geometry. One may thus conduct tension fatigue tests with STS alone in order to model the tension fatigue life of rubbers with alternate geometry.     

Impact-induced fatigue of foamed polymers

The fatigue life of foamed polymers in compression impact was measured using a cam-driven compound pendulum system. Impact-induced fatigue data are presented for two open-celled foamed polymers having different densities, which are often used for shock mitigation. Material measurements at constant incident energy included the static compression modulus and peak dynamic stress, which progressively degraded as the number of impacts approached one million. Other indicators of fatigue life were cell breakdown, in which microscopic edge cracks were observed in both dry and water-saturated test specimens. The dry material had the longer fatigue life. In both cases, cell breakdown occurred after a million or more impacts at peak compressive stresses in the 200–300 kN/m² range.     

高应力水平下滚动轴承疲劳寿命试验研究

通过在三种不同的强化负荷下进行深沟球轴承疲劳寿命试验，并与常规试验一组结果对比。结果表明，适当地加大滚动轴承疲劳寿命试验负荷，可以大大缩短试验时间，而疲劳寿命依然服从Ｗｅｉｂｕｌ分布，且与常规试验结果基本一致，同时疲劳破坏的形式仍是表面下萌生裂纹，然后扩展至表面形成剥落。     

Bayesian Analysis of Step‐Stress Accelerated Life Test with Exponential Distribution

In this article, we propose a general Bayesian inference approach to the step‐stress accelerated life test with type II censoring. We assume that the failure times at each stress level are exponentially distributed and the test units are tested in an increasing order of stress levels. We formulate the prior distribution of the parameters of life‐stress function and integrate the engineering knowledge of product failure rate and acceleration factor into the prior. The posterior distribution and the point estimates for the parameters of interest are provided. Through the Markov chain Monte Carlo technique, we demonstrate a nonconjugate prior case using an industrial example. It is shown that with the Bayesian approach, the statistical precision of parameter estimation is improved and, consequently, the required number of failures could be reduced. Copyright © 2011 John Wiley & Sons, Ltd.     

60Si2Mn弹簧扁钢疲劳试验断裂分析

对60Si2Mn弹簧扁钢进行了疲劳寿命试验.试验结果,疲劳寿命达到标准要求(＞8×104次).采用化学分析、断口扫描、硬度测定和金相检验等方法,对疲劳试验中的断裂件进行了分析.分析结果表明,疲劳断裂产生在总成型式试样的同一位置,裂源萌生处有夹杂物;回火组织中出现少量贝氏体.根据显微组织和硬度检测结果,适当调整热处理工艺,可进一步提高弹簧的疲劳寿命.     

Fatigue failure of a star–ratchet gear

We present an analysis of the fatigue failure of an 18 tooth star–ratchet gear (SRG). The subject gear was implemented in the freewheel assembly of a mountain bicycle. After 6 years of service, the gear failed unexpectedly during a typical off-road ride. The unique geometry of SRGs precluded a simple comparison to existing gear lifetimes. Scanning Electron Microscopy (SEM) analysis of the failed gears showed crack initiation at the root of the gear teeth, followed by fatigue crack propagation and eventual chip-out. A biomechanical analysis of pedaling forces, coupled with explicit power data obtained from instrumented rides over the same trails, in conjunction with a Finite Element Analysis (FEA) of the gear, were used to determine stress amplitudes for fatigue calculations. Energy dispersive spectroscopy (EDS) determined the alloy composition of the gear and thus set the strength and fatigue properties of the gear. Basquin’s law, Goodman’s mean stress correction, and Miner’s rule were used to estimate the lifetime, in bike rides, of the gear. Our analysis led to an estimate of 2288 rides, while failure was reported after roughly 312 rides. Given the uncertainties in fatigue life estimation and service use, we find this estimate acceptable.     

用加速寿命试验法研究瓦楞纸箱寿命初探

选用空气相对湿度H和垂直载荷G为加速应力,用加速寿命试验法对瓦楞纸箱寿命进行研究,建立了瓦楞纸箱双应力加速方程,并计算出正常工作应力下瓦楞纸箱的平均寿命及可靠度。     

A Comparison of Accelerated Test Plans to Estimate the Survival Probability at a Design Stress

In a previous paper [3], the authors presented large sample optimum accelerated test plans to estimate the survival probability at a design stress assuming a linear logistic model, i.e. a linear relationship between stress and the log survival odds at that stress. The optimum plans required testing at two accelerated stresses with a larger allocation of units assigned to the lower of the two stresses. In practice, however, it is often desirable to conduct the accelerated tests at more than two stresses and/or use equal or otherwise prespecified allocation. In this paper we compare the large sample variance of each of ten such non-optimum test plans (and also that of testing exclusively at the design stress) with that of the optimum plan under a variety of conditions.     

船舶防污漆加速试验方法研究

本文介绍了把防污涂料防污性能的静态实验和动态试验，动、静态渗毒率测试，ＳＰＣ型自抛光防污漆降阻性能测试，漆膜形态剖析等有机结合建立起的一套切实可行的加速试验方法和配套设施。采用该方法可在１年内评定出３年防污期效的防污漆。     

Asymptotically Optimum Over-Stress Tests to Estimate the Survival Probability at a Condition with a Low Expected Failure Probability

This paper is concerned with the optimum allocation of test units to overstress conditions when it is desired to estimate the survival probability at a design condition with a low expected failure probability. The criterion is that of minimizing the large sample variance: a logistic model is assumed. Expressions and charts for allocating test units to the accelerated stresses are provided and procedures for determining the stresses when these are not all specified are given. The gain in efficiency from using these plans versus testing exclusively at the design condition is analyzed. The requirement for some testing at the design stress and at an intermediate stress is also considered.