Parametric Accelerated Life Testing Research Articles

Structured Method to Reconfigure the Fatigue of Mechanical Products such as HKS in a Refrigerator

To determine the fatigue lifetime of a system such as a car, refrigerator, etc., parametric Accelerated Life Testing (ALT) can be used as an arranged way to find out its reliability and failure mechanisms a when it is subjected to continual loads The process includes: (1) parametric ALT used to establish the BX life, (2) load evaluation for designing an accelerated life test(s), (3) a tailored representative of ALTs with design adjustments, and (4) an appraisal of whether system gets to the goal for the BX lifetime. A generalized life-stress failure approach with an accelerated factor, and sample size formulation are proposed. An organized reliability approach, such as parametric ALT, can help the designer to find product defects having an effect on reliability as computed by the improvement in life, LB, and the decreasing in failure rate, λ in the design stage. As a consequence, manufacturers can stop recalls from failures of their products when introduced into the marketplace. A hinge kit system (HKS) in a domestic refrigerator that needed to be redesigned was provided as an example. After a tailored set of parameter ALTs, the HKS with design changes were expected to realize the life aim – B1 life ten years.

Improving the lifetime of mechanical systems during transit established on quantum/transport life-stress prototype and sample size

Parametric accelerated life testing (ALT) with the reliability quantitative (RQ) statements is offered as a reliability methodology to identify and rectify design flaws. The methodology includes: (1) BX lifetime with ALT scheme, (2) fatigue design, (3) ALTs with alterations, and (4) discernment whether the design(s) obtains targeted BX life. A quantum/transport-based life-stress prototype and sample size for generating RQ specifications were suggested. The equivalent elevated damage potential in parametric ALT was applied, represented by a field power spectral density (PSD). A case study was used to evaluate refrigerator fatigue failures that occurred during rail transport. In the 1st ALT, for RQ specifications, the refrigerator tubes made of ethylene propylene diene monomer (EPDM) rubber fractured because of the compressor mount design. The failure in the 1st ALT was similar to those found from failed refrigerators in the field. After the compressor mounts and tubes were redesigned, there were no difficulties during the 2nd ALT. The refrigerator was then assured to fulfil a B1 lifetime for required travel distance.

Enhancing the Fatigue of Mechanical Systems Such as Dispensers Entrenched on Generalized Life-Stress Models and Sample Sizes

To lengthen the life of a mechanical system, parametric accelerated life testing (ALT) is recommended as an established way to help identify structural imperfections and reduce fatigue-related failures. It involves (1) a parametric ALT scheme, (2) fatigue design, (3) ALTs with alterations, and (4) an estimate of whether design(s) achieve the BX lifetime. The application of a quantum-transported time to failure prototype and a sample size expression is also suggested. The improvements in the reliability of a water dispenser made of stainless steel or polypropylene (PP) in a bottom-mount domestic refrigerator was used as a case study. In the first ALT, the hinge and front corner of the dispensing system was cracked. The water dispenser lever was altered by increasing the thickness of its ribs and fillets. In the second ALT, the altered dispensing lever system cracked because there was an insufficient thickness in its front corner for impact loading. The critical design factors for improving reliability were corner fillet rounding and rib thickening in a dispenser lever. As there were no difficulties in the third ALT, the dispenser life was verified to have a B1 life of 10 years.

Systematic Methods to Increase the Lifetime of Mechanical Products Such as Refrigerators by Employing Parametric Accelerated Life Testing

This investigation practically explains the implementation of parametric accelerated life testing (ALT) as an algorithm to recognize design imperfection and rectify it in creating a reliable quantitative (RQ) statement by sample size equation. It covers: (1) a module BX life that X% of a collection of system items is unsuccessful with an ALT plan, (2) design for fatigue, (3) ALTs with alterations, and (4) discernment as to if the final design(s) obtains the targeted BX lifetime. A (generalized) life–stress formulation by the linear transport process is recommended for the mathematical work of the parametric model. As a case study, an ice-maker including gear system in a refrigerator was utilized. The gear teeth made of cast iron (carbon, 3 wt% and silicon, 2 wt%) was fracturing in a refrigerator ice-maker. To reproduce the field failure and rectify the problematic designs in the marketplace, a parametric ALT was carried out. At the first ALT, the gear teeth made of cast iron partly cracked and fractured under severe cold conditions (below −20 °C) in the freezer. It was modified by changing the material from cast iron to a sinter-hardened powder metallurgy nickel steel because high fatigue strength in the low temperature was required. At the second ALT, we discovered the fractured helix made of polycarbonates (PC). As a modification, strengthened rib on the front and side of the helix the thickness of gear teeth was attached. At the third ALT, there was no concern, and the life of the auger motor including gear system was manifested to have a B1 life 10 years.

Systematic Methods to Enhance the Life of Mechanical System Such as Compressor Subjected to Repetitive Impact Load

To improve the life of mechanical product, parametric Accelerated Life Testing (ALT) as reliability methodology proposes to assess the design of mechanical products subjected to repeated loads, based on (generalized) life-stress formulation and sample size equation. It will help an engineer to reveal the design defects of the mechanical product which making a critical influence on product reliability for the design procedure. Eventually, companies can circumvent product recalls due to the design flaws from the marketplace. As an experiment example, the redesign of compressor in a domestic refrigerator was studied.

Process to Establish the Enhance of Fatigue Life of New Mechanical System Such as a Drawer by Accelerated Tests

To extend the life of a mechanical system, parametric Accelerated Life Testing (ALT) is proposed as a procedure to identify design faults and reduce fatigue failure. It includes a derivation of generalized time to failure model by linear transport process and a sample size equation for the ALT. A refrigerator drawer was used as an example. After loading, the rail rollers broke and the center support was bent. Ribs were added to the center support and the rail roller support was extended. At the first ALT, the box cover failed near the intersection between the cover and body. The box was then modified by increasing the rib and fillet. At the second ALT, the rails and center support fractured. They were altered by increasing the rib and corner rounding. After the third ALT, there were no issues. The drawer lifetime was ensured to be B1 life 10 years.

Enhancing the Lifetime of the Pneumatic Cylinder in Automatic Assembly Line Subjected to Repeated Pressure Loading

This study demonstrates the application of parametric accelerated life testing (ALT) as a procedure to identify design deficiencies and correct them in generating a reliable quantitative (RQ) specification. It includes: (1) a system BX lifetime that X% of a product population fails with a parametric ALT scheme, (2) fatigue design, (3) ALTs with alternations, and (4) judgement as to whether the design(s) secures the desired BX lifetime. A (generalized) life–stress model through the linear transport process and a sample size formulation are suggested. A pneumatic cylinder in a machine tool was used as a case study. The cylinder was failing in a flexible manufacturing system. To reproduce the failure and modify the design, a parametric ALT was performed. At the first ALT, the metal seal made of nickel-iron alloy (36% Ni) partially cracked and chipped and had a crisp metal sound. It was modified by changing the seal from a metal to a polymer (silicone rubber). At the second ALT, the piston seal leaked due to seal hardening and wear. The failure modes of the silicone seal in the laboratory tests were similar to those returned from the field. For the third ALT, the seal material was changed from silicone rubber to (thermoset) polyurethane. There were no concerns during the third ALT and the lifetime of the pneumatic cylinder was shown to have a B1 life of 10 years.

Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) as a way to recognize design defects in mechanical products in creating a reliable quantitative (RQ) specification. It covers: (1) a system BX lifetime that X% of a product population fails, created on the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an evaluation of whether the system design(s) acquires the objective BX lifetime. A life-stress model and a sample size formulation, therefore, are suggested. A refrigerator compressor is used to demonstrate this method. Compressors subjected to repetitive impact loading were failing in the field. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The failure modes of the suction reed valves were similar to those valves returned from the field. The fatigue failure of the suction reed valves came from an overlap between the suction reed valve and the valve plate in combination with the repeated pressure loading. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). After these design modifications, there were no troubles during the third ALT. The lifetime of the compressor was secured to have a B1 life of 10 years.

Improving lifetime of domestic compressor subjected to repeated pressure loading

To enhance the lifetime of domestic refrigerator compressors subjected to repeated pressure loads, parametric accelerated life testing (ALT) as a reliability methodology is studied. It contains (1) ALT plan used on BX lifetime, (2) load analysis for the ALT, (3) parametric ALTs with action plans, and (4) assessment of the last compressor designs to make sure the targeted BX lifetime is achieved. To combine the design concepts of a compressor with parametric ALT, we have derived the approximated sample size equation, the life-stress model with an effort concept and acceleration factor. As a test case, a compressor with a newly designed crankshaft subjected to repetitive pressure loading was studied. Based on a mass and energy balance, the compressor loads were analyzed. In the 1st ALT, the failure mode was locking of the compressor due to crankshaft wear. The design fault of the crankshaft was the improper lubrication in the crankshaft. As a corrective action plan, the crankshafts were redesigned by: (1) changing the starting RPM from 1650 to 2050, (2) relocating the lubrication holes and adding a new groove, and (3) modifying the material of crankshaft from FCD450 to FCD500. In the 2nd ALT, wear on the surface of compressor crankshaft occurred. The minimum clearance between thrust washer and the crankshaft was then modified. After three parametric ALTs, the lifetime of the newly designed compressor was guaranteed to have B1 life 10 years.

Improving the Fatigue of Newly Designed Mechanical System Subjected to Repeated Impact Loading

This paper develops parametric accelerated life testing (ALT) as a systematic reliability method to produce the reliability quantitative (RQ) specifications—mission cycle—for recognizing missing design defects in mechanical products as applying the accelerated load, expressed as the inverse of stress ratio, R. Parametric ALT is a way to enhance the prediction of fatigue failure for mechanical systems subjected to repeated impact loading. It incorporates: (1) A parametric ALT plan formed on the system BX lifetime, (2) a fatigue failure and design, (3) customized ALTs with design alternatives, and (4) an assessment of whether the last design(s) of the system fulfills the objective BX lifetime. A BX life concept with a generalized life-stress model and a sample size equation are suggested. A domestic refrigerator hinge kit system (HKS), which was a newly designed mechanical product, was used to illustrate the methodology. The HKS was subjected to repeated impact loading resulting in failure of the HKS in the field. To conduct ALTs, a force and momentum balance was utilized on the HKS. A straightforward impact loading of the HKS in closing the refrigerator door was examined. At the first ALT, the housing of the HKS failed. As an action plan, the hinge kit housing was modified by attaching inside supporting ribs to the HKS to provide sufficient mechanical strength against its loading. At the second ALT, the torsional shaft in the HKS made with austenitic ductile iron (18 wt% Ni) failed. The cracked torsional shaft for the 2nd ALTs came from its insufficient rounding, which failed due to repeated stress. As an action plan, to have sufficient material strength for the repetitive impact loads, the torsional shaft was reshaped to give it more rounding from R0.5 mm to R2.0 mm. After these modifications, there were no problems at the third ALT. The lifetime of the HKS in the domestic refrigerator was assured to be B1 life 10 years.

Reliability design of mechanical systems subjected to repetitive stresses

To enhance the design of mechanical systems, parametric Accelerated Life Testing (ALT) as a systematic reliability method is proposed as a way to evaluate the design of mechanical systems subjected to repeated impact stresses. It requires: (1) a parametric ALT scheme shaped on system BX lifetime, (2) a load inspection, (3) parametric ALTs with the associated design modifications, and (4) an assessment of whether the revised product design(s) reach the targeted BX life-time. We propose using a general life-stress model and sample size equation. A test example using both market data and parametric ALT was the redesign of a hinge kit system (HKS) in a refrigerator. To conduct parametric ALTs, a force and moment balance analysis was utilized. The mechanical impact loadings of the HKS were evaluated for an working refrigerator door. For the first ALT, the HKS failure happened in the crack/fracture of the kit housing and oil spilled from the damper when the HKS was disassembled. The failure modes and mechanisms constructed in the 1st ALT were similar to those of the unsuccessful samples found from the marketplace. The missing design parameters of the HKS included stress raisers such as corner roundings and the rib of the housing in HKS, the seal in the oil damper, and the material of the cover housing. In the second ALT, the cover housing fractured. The design defect of the cover housing in the HKS was the plastic material. As a corrective action plan, the cover housing was modified from plastic to aluminium. After the second ALT, the lifetime of the modified HKS was reassured to be B1 life 10 years with a yearly failure rate of 0.1%.

Improving the Lifetime of Mechanical System Such as Hinge Kit System Subjected to Repeated Impact Stress

To enhance the lifetime of mechanical system, parametric Accelerated Life Testing (ALT) as new systematic reliability method suggests evaluating the design of mechanical systems subjected to repeated stresses, based on failure mechanism and design. This newly developed parametric ALT helps an engineer uncover the missing design parameters (or design flaws) of the mechanical system having an effect on reliability during the product developing process. As a result, companies can circumvent product recalls due to the design flaws from the marketplace. As an experiment instance, the redesign of hinge kit system (HKS) in a domestic refrigerator was investigated.

Reliability Design of Mechanical Systems Subjected to Repetitive Stresses

To improve the lifetime of mechanical system, parametric Accelerated Life Testing (ALT) as new reliability methodology suggests to assess the design of mechanical systems subjected to repetitive stresses. It includes: (1) a parametric ALT plan based on product BX lifetime, (2) a load analysis for accelerated life time test, (3) a tailored sample of parametric ALTs with the design modifications, and (4) an evaluation of whether the final design(s) of the product achieves the target BX lifetime.

Improving fatigue of mechanical systems such as freezer drawer subject to repetitive stresses

Parametric accelerated life testing (ALT) as a methodology of reliability tests is suggested as a way to identify and reduce the fatigue failure of mechanical systems. It consists of a parametric accelerated life testing plan, fatigue failure and design, and accelerated testing with action plans to ensure the product achieves its expected lifetime target. A generalized life-stress failure model with an effort concept and sample size equation are derived. As a case study, the reliability of a newly designed freezer drawer is evaluated. In the first accelerated life testing, the handles were fracturing because of a design flaw that appeared during the repetitive openings and closings of the freezer drawer with the food in the drawers. Increasing the total handle width provided an improved design that corrected the failures with the handles. In the second accelerated life testing, the slide rails also fractured because they did not have enough strength to withstand repetitive opening and closing of the drawers with the typical food loads in the drawers. To improve the design of the slide rails, supplementary reinforced ribs, reinforced boss, and an inner chamber were added. After three rounds of parametric accelerated life testing, the modified freezer drawer was expected to achieve the lifetime of B1 life 10 years.

Reliability design and case study of the domestic compressor subjected to repetitive internal stresses

To improve the lifetime of mechanical system such as compressor, parametric accelerated life testing (ALT) as a reliability methodology is suggested. It consists of (1) a parametric ALT plan based on BX lifetime, (2) load analysis for accelerated lifetime test, (3) a tailored series of parametric ALTs with action plans, and (4) evaluation of the final compressor design to ensure the targeted BX lifetime is satisfied. As a test case, failed reciprocating compressors of French-door refrigerators returned from the field were studied. Disassembling the compressors revealed that the suction reed valve had fractured. In the first ALT, the failed samples from the field were reproduced. The root cause of the failures came from the sharp edges of the valve plate and an overlap between the suction reed valve and the valve plate. Corrective actions included modifying the valve plate in the compressor system to increase the trepan size and adding a ball peening process to eliminate sharp edges on the valve plate. There were no problems during the second ALT. After these parametric ALTs with corrective action plans were conducted, the modified compressor was expected to achieve lifetime of B1 life 10 years.

Reliability design and case study of mechanical system like a hinge kit system in refrigerator subjected to repetitive stresses

To improve the reliability of mechanical systems with inherited faulty designs, a reliability methodology utilizing parametric accelerated life testing (ALT) is suggested. It consists of: 1) a parametric ALT plan, 2) a load analysis, 3) a tailored series of parametric ALTs with action plans, and 4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer uncover the design parameters affecting reliability during the design process of a mechanical system. As a case study, the hinge kit system (HKS) of a door in a refrigerator was redesigned to improve its reliability. Using a force and moment balance analysis, the mechanical impact loads in closing the door of the HKS were calculated. During the first ALT, the kit housing in the HKS fractured and the oil damper leaked when the HKS failed. The faults in the design of the HKS included the weakness of the housing hinge kit and the oil sealing structure of the oil damper. In the second ALT, the hinge cover fractured due to the impact of the damper support. The material in the hinge cover in the HKS was changed from plastic to aluminum. After three rounds of parametric ALTs, the reliability of the new HKS was guaranteed to be a 10 year life with an accumulated failure rate of 1%.

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a load analysis, (3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer reproduce the fractured or failed parts in a product subjectedto repetitive loading and correct the faulty designs. As a test case, the helix upper dispenser of a refrigerator ice-maker fractured in field was studied. Using a load analysis, we discerned that the helix upper dispenser fracture was due to repetitive loads and a faulty design with a 2 mm gap between the blade dispenser and the helix upper dispenser. During the first and second ALTs, the fracture in the helix upper dispenser was reproduced. The failure modes and mechanisms found were similar to those of the failed sample in field. As an action plan, the design of the helix upper dispenser was modified by eliminating the 2 mm gap and adding enforced ribs. In the third ALT there were no problems. After three rounds of parametric ALTs, the reliability of the helix upper dispenser was guaranteed as a 10-year life with an accumulated failure rate of 1%.

Improving the Reliability of the Design of a Freezer Drawer in a French Door Refrigerator Subjected to Repetitive Food Loading

Background: A freezer drawer in a French door refrigerator subjected to repetitive food loading was found to have fractured in the field. Inspection of the field failures was carried out to determine the root causes in the design failures of the drawer. The primary failures came from a faulty design of the drawer that was not strong enough to withstand the loads caused by repetitive open and closing of the drawer. Objective: Based on the analysis of field data and a tailored set of parametric Accelerated Life Tests (ALT), the freezer drawer system for food storage in the French refrigerator was redesigned to improve its reliability. Methods: To carry out parametric Accelerated Life Tests (ALTs) using a force balance analysis, the simple mechanical loads of the drawer system were evaluated and an accelerated factor was found. Sample size equations with accelerated factors also were derived and used. Results: For the first ALT, the handle of the freezer drawer was fractured. The failed shapes found in the tests were similar to those of the failed samples from the field. The drawer was redesigned by increasing the width of the reinforced handle. During the second ALT, the slide rails were fractured. Conclusion: After the parameter ALTs, a corrective action plan was developed. The reliability of the newly designed freezer drawer system was assured to have a B1 life of 10 years with a failure rate of 0.1%/year. Recent patents on French refrigerators were also addressed. Keywords: Accelerated factor, freeze drawer system, missing design parameter, parametric accelerated life testing, reliability design, sample size equation.

Improving the Reliability of the Cooling Enclosure System in a Refrigerator

Background: Aluminum tubes of a refrigerator evaporator were having pitting problems in the field. A failure analysis was performed using a scanning electron microscopy with energy dispersive x-ray analysis. The root cause of the problematic evaporator tubes was identified as the chlorine in a cotton adhesive tape that was used to fasten the evaporator tube to the inner case. The crevice (or pitting) corrosion mechanism occurred on the evaporator tube surface. Methods: A variety of chemical reactions were analyzed. To reproduce the pitting corrosion on the evaporator tube, a parametric accelerated life testing was performed using a 20% saline solution on the evaporator tube that was wetted in the chlorine water. Results: It showed that the evaporator tube was pitted in a place where the cotton tape was attached. The failure modes and mechanisms validated experimentally were identical to those of the problematic refrigerators in field. To modify the problem with the refrigerator evaporator tube, the cotton tape was changed into a generic transparent tape. Conclusions: The reliability of the new design for the cooling enclosure system pitted in field is now expected to have B1 life of over 10 years. Keywords: Evaporator tube, missing design parameter, nomenclature, parametric accelerated life testing, pitting corrosion, reliability design.

Reliability Design of Ice-Maker System Subjected to Repetitive Loading

Parametric Accelerated Life Testing (ALT) was used to improve the reliability of ice-maker system with a fractured helix upper dispenser in field. By using bond graphs and state equations, a variety of mechanical loads in the assembly were analyzed. The acceleration factor was derived from a generalized life-stress failure model with a new load concept. To reproduce the failure modes and mechanisms causing the fracture, new sample size equation was derived. The sample size equation with the acceleration factor also enabled the parametric accelerated life testing to quickly reproduce early failure in field. Consequently, the failure modes and mechanisms found were identical with those of the failed sample. The design of this testing should help an engineer uncover the design parameters affecting the reliability of fractured helix upper dispenser in field. By eliminating the design flaws, gaps and weldline, the B1 life of the redesign of helix upper dispenser is now guaranteed to be over 10 years with a yearly failure rate of 0.1% that is the reliability quantitative test specifications (RQ).