Reliability design and case study of a refrigerator compressor subjected to repetitive loads

A newly designed crankshaft of a compressor for a side-by-side (SBS) refrigerator was studied. Using mass and energy conservation balances, a variety of compressor loads typically found in a refrigeration cycle were analyzed. The laboratory failure modes and mechanisms were compressor locking and crankshaft wear. These were similar to those of the failed samples in the field. Failure analysis, accelerated life testing (ALT), and corrective actions were used to identify the key reliability parameters. The design parameters of the crankshaft included the hole locations and the groove of the crankshaft used for oil lubrication, crankshaft hardness, and thrust washer interference. Based on the analysis and design changes, the B₁ life of the new design is now over ten years with a yearly failure rate of 0.01 percent. A five step procedure is recommended for parts design.     

Design of a hinge kit system in a Kimchi refrigerator receiving repetitive stresses

Based on field data and a tailored set of accelerated life tests, the hinge kit system of a closing door in a Kimchi refrigerator was redesigned. Using a force and moment balance analysis, the simple mechanical loads from the closing of the door were evaluated. The failure modes and mechanisms found experimentally were similar to those of the failed sample 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 hinge kit system. The missing controllable design parameters of the hinge kit system in the design phase included the corner rounding and rib of the housing hinge kit, the oil sealing method of the oil damper, and the material of the cover housing. After a tailored series of accelerated life tests with corrective action plans, the B₁ life of the new hinge kit design is now guaranteed to be over 10 years with a yearly failure rate of 0.1%.     

Reliability design of a reciprocating compressor suction reed valve in a common refrigerator subjected to repetitive pressure loads

The compressor in a commercial refrigerator was redesigned to improve its reliability. The compressor used in the refrigerator had been failing due to fracturing of the suction reed valve. Failure analysis, accelerated life tests and corrective action plans were used to identify the key control parameters and levels for the mechanical compressor system. The failure modes and mechanisms found experimentally were similar to those of the failed sample in the field. The missing controllable design parameters of the compressor system in the design phase were an overlap with the valve plate, a weak material [SANDVIK 20C 178t], and the sharp edge of the valve plate. After a tailored series of accelerated life tests with corrective action plans, the reliability of the new compressor system is now guaranteed to be 12.6 years with a yearly failure rate of 0.06%.     

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%.     

Failure mechanism in SMC subjected to alternating stresses

Failure mechanisms in randomly reinforced sheet moulding compounds subjected to fatigue testing were studied by relating the changes in characteristic mechanical properties to microscopic changes in the material. It was demonstrated that various mechanisms take place simultaneously to an extent that depends on the local microstructure and strength and that the collective interplay of these mechanisms is responsible for failure. As damage progresses, a uniform pattern of cracks is formed in the matrix, and Mode II fibre/matrix-interfacial failure occurs. The mechanisms concerned can be explained by calculating the forces transmitted between the fibres and the matrix. It was observed that different load amplitudes gave rise to equivalent damage patterns in the material. In the light of this fact and with the aid of the failure mechanisms identified, a method has been devised, by means of which the fatigue life can be estimated of SMC exposed to alternating loads ef any given amplitude.     

Induction of optical vortex in the crystals subjected to bending stresses

We describe a method for generation of optical vortices that relies on bending of transparent parallelepiped-shaped samples fabricated from either glass or crystalline solid materials. It is shown that the induced singularity of optical indicatrix rotation leads in general to appearance of a mixed screw-edge dislocation of the phase front of outgoing optical beam. At the same time, some specified geometrical parameters of the sample can ensure generation of a purely screw dislocation of the phase front and, as a result, a singly charged canonical optical vortex.     

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%.     

Evolution of residual stresses in a stress-free titanium alloy subjected to fretting fatigue

This study investigated the complete history of residual stress evolution in a stress-free titanium alloy, Ti–6Al–4 V under fretting fatigue loading condition. Compressive residual stress developed in the contact region due to the local plastic deformation between contacting bodies. The compressive residual stress then increased initially with increasing number of fretting fatigue cycles reaching to a maximum value, and then it decreased (or relaxed) with further cycling. This relaxation of compressive residual stress was due to the delamination and detachment of flake-like (wear sheet) material in the fretted region.     

Prediction of stresses in concrete pavements subjected to non-linear gradients

This paper presents a technique for analyzing the residual stresses in concrete pavements subjected to non-linear (stress or strain) gradients throughout the slab thickness. The analysis is separated into two parts. In the first part, an expression is presented for calculating the self equilibrated stresses within a cross-section due to internal restraints (i.e. satisfying equilibrium conditions and continuity of the strain field within the cross-section). These stresses are independent of slab dimensions and boundary conditions. In step two, the stresses due to external restraints (i.e. self-weight and subgrade reaction) are calculated using an equivalent linear temperature gradient obtained from the first part and using existing closed form solutions by Westergaard [Westergaard, H. M., Computation of stresses in concrete roads. In Proc. of the 5th Annual Meeting, Vol. 5, Part I, Highway Research Board, 1926, pp. 90–112] or Bradbury [Bradbury, R. D., Reinforced Concrete Pavements. Wire Reinforcement Institute, Washington D.C., 1947.]. The solution to this step includes slab length and boundary conditions. Total internal stresses due to non-linear gradients are obtained using the superposition principle. The proposed method has been applied to field data from another study for varying temperature profiles within a 24 h period and compared to results from conventional analysis assuming linear gradients. Significant differences were found between the two methods for night-time and early-morning conditions. A linear gradient solution sometimes underestimates tension in the bottom of a slab prior to vehicle loading by a factor of three.     

Failure rate behavior of components subjected to random stresses

This paper presents a theoretical study of the failure rate behavior of components subjected to random environmental stresses. Three kinds of stresses are considered: point, alternating, diffused. The concept that the component could memorize the stress is introduced. Diverse types of stress action can thus be defined: instantaneous, cumulative, recovering. Two classes of stochastic models are proposed, which express the effect of stress to the lifetime of the component. Several examples for which the resulting failure rate has an explicit expression, are presented. In most of these examples, the failure rate converges rapidly to a constant, that confirms a conjecture frequently made by the engineers.     

Fatigue strength of fillet welds subjected to multi-axial stresses

Fatigue endurance assessments of welded details are normally carried out by calculating the relevant stress acting on the detail and identifying a relevant fatigue class (or detail category) with its associated S–N curve. The fatigue strength of most structural details incorporated in design codes has been obtained from fatigue tests conducted under uni-axial loading conditions, which normally result in a uni-axial stress state in the detail. Many of the structural details that exist in fatigue-loaded structures experience some kind of multi-axial loading condition. The subject of the fatigue strength of welded details under multi-axial loads has been the topic of numerous research projects in recent years. The vast majority of these projects were, however, devoted to cracking in the base metal (i.e. toe cracking). Very little has been done with reference to the cracking of fillet welds in combined loading situations (i.e. root cracking). This paper presents new test results from cruciform specimens, in which weld failure initiated at the root in a multi-axial stress state. The tests have been performed at two different load levels and on three different specimen configurations giving different τ/σ ratios. This permitted an examination of the effect of the shear to normal stress ratio on the fatigue strength of fillet welds. The results of these tests, together with other relevant tests reported in the literature, are then evaluated in relation to the design models proposed in three design standards: Eurocode, IIW and DNV. No obvious dependence on the τ/σ ratios could be found. The evaluated models all appear to be able to predict the fatigue life of a cruciform weld failing from the root under combined shear and normal stress.     

Thermo-elasto-plastic stresses in functionally graded materials subjected to thermal loading taking residual stresses of the fabrication process into consideration

Functionally graded materials (FGMs) have recently been received with considerable interest, primarily as high temperature resistant materials for space vehicles subjected to high temperature environment. FGMs are one of the composite materials and consist of continuous change of composition of different material components from one surface to the other. FGMs usually fabricated at high temperature at which the FGMs have stress free condition. After the FGMs cooled from the fabrication temperature to the room temperature residual thermal stresses produced. In this paper, elasto-plastic thermal stresses in a rectangular plate (FGP) of a particle reinforced composite FGM are treated by finite element method due to the microscopic combination law when the FGP is subjected to three kinds of temperature conditions, first is cooling from the fabricated temperature to the room temperature, second is heating and last is heating after cooling from the fabricated temperature. In the analysis, the thermal stress constitutive equation of a particle-reinforced composite taking temperature change and damage process into consideration is used. The effects of the particle volume fraction and the three kinds of temperature conditions on the stresses in the matrix, stresses in the particle and macroscopic stress are discussed.     

钢筋混凝土柱式墩落石冲击抗剪性能可靠性分析

建立一种基于可靠度理论的落石冲击作用下钢筋混凝土柱式桥墩抗剪性能可靠性分析方法。在数值分析方法可靠性验证基础上通过非线性有限元分析生成了60组落石-墩柱接触力时间过程数值样本,考虑等冲量和等峰值建立落石撞击荷载的简化半波正弦模型;以Priestley公式描述墩柱抗剪能力,以剪力破坏参数定义墩柱损伤等级,通过蒙特卡洛随机抽样得到各撞击强度下结构失效概率,进而得到易损性曲线,进行了落石质量、撞击速度、墩柱截面面积、混凝土轴心抗压强度和箍筋配筋率参数敏感性分析。结果表明,数值模型参数能够有效模拟钢筋混凝土构件落石冲击响应;相比于全局平均等效静力,峰值等效静力方法更适用于落石冲击荷载等效静力简化;落石质量和撞击速度增加不同程度增加墩柱抗剪失效概率,混凝土轴心抗压强度提高、墩柱截面面积增加和箍筋加密一定程度上降低墩柱各个等级损伤发生概率。     

A numerical technique for the analysis of cracks subjected to normal compressive stresses

The purpose of the present paper is the development of a numerical method for the evaluation of the Stress Intensity Factor in mode II at the tips of closed cracks subjected to compressive normal stresses and monotonically increasing shear stresses. A hybrid Boundary Element Technique, originally developed for the analysis of open cracks, has been suitably modified. The Stress Intensity Factor is evaluated directly on the basis of the displacement discontinuities computed at the crack tip element, by taking into account the development of frictional resistance on the crack surfaces. A limited number (10-15) of displacement discontinuity elements is found to be sufficient for an accurate evaluation of the Stress Intensity Factor. Some basic aspects of the mechanical behaviour of closed cracks are also investigated on the basis of the proposed method.     

Analysis for the interlaminar stresses of thin layered composites subjected to thermal loads

Accurate stress analysis of layered material systems that are sometimes very thin is of great importance in the assessment of their structural integrity and performance. To give satisfactory results, the discretised meshes of the conventional domain solution techniques, such as the finite element method, must have reasonable aspect ratios in the same order of magnitude. Therefore, the domain modeling of ultra-thin structures, such as the facings of sandwich composites and adhesive layers, shall require an enormous amount of discretised meshes that may incur overloading computations. Using the boundary element method as an alternative, the present work proposes an effective approach to analyze the interlaminar stresses of thin layered composites subjected to general thermal loads. The transformed boundary integral equation for anisotropic thermoelasticity is fully regularized using the technique of integration by parts and analytical integration. At the end, the veracity and applicability of the proposed scheme are demonstrated by numerical examples.