Warranty Period Research Articles

Use-level lifetime distribution estimation under dependent right censored test data

Accelerated life testing (ALT) is a practice for estimating unit reliability at normal use conditions using failure data obtained under more severe test conditions. We focus on life tests where a potential critical unit failure at X2 (unit lifetime) may be avoided by a degraded failure at some random time X1. Degraded and critical failures are linked through the degradation process,hence the situation under consideration is that of dependent competing risks. We apply the general result that if the copula C(.; .) of (X1; X2) is known, competing risks data uniquely determine the marginal distributions at each stress level. Interest here (and in life testing studies in general) is in unit lifetime. Accordingly, our target of estimation is to extrapolate a use-level lifetime distribution from which important reliability measures such as mean lifetime, warranty period among others are derived. The paper is based in part on a PhD thesis by Hove (2014).

Acquisition Pricing and Inventory Decisions on Dual-Source Spare-Part System with Final Production and Remanufacturing

The life spans of durable goods are longer than their warranty periods. To satisfy the service demand of spare parts and keep the market competition advantage, enterprises have to maintain the longer inventory planning of spare parts. However, how to obtain a valid number of spare parts is difficult for those enterprises. In this paper, we consider a spare-part inventory problem, where the inventory can be replenished by two ways including the final production order and the remanufacturing way. Especially for the remanufacturing way, we consider the acquisition management problem of used products concerning an acquisition pricing decision. In a multiperiod setting, we formulate the problem into a dynamic optimization problem, where the system decisions include the final production order and acquisition price of used products at each period. By stochastic dynamic programming, we obtain the optimal policy of the acquisition pricing at each period and give the optimal policy structure of the optimization problem at the first period. Then, a recursion algorithm is designed to calculate the optimal decisions and the critical points in the policy. Finally, the numerical analyses show the effects of demand information and customer’s sensitive degree on the related decisions and the optimal cost.

Investigation of the process of aging cold rolled and hot dip rolled products of high-strength automotive steels for cold deformation

The paper studied the aging process of cold rolled and hot dip rolled products of high-strength automotive steels have good formability, weldability and resistance to dents. The article presents data on the timing guarantees the mechanical properties of metal-roll production of OJSC Magnitogorsk Iron and Steel Works (MMK) in the storage and processing of consumers. For experimental studies were selected following assortment: galvanized rolled steel grades A341-A5, HX180BD, HX220YD, 006 / IFGR and cold-rolled steel grades and HC220Y 006 / IFCR production of rolling mill № 11 OJSC MMK. In laboratory conditions were simulated to ensure that the flow of natural and artificial heat, strain and thermal-aging. To determine the change in mechanical properties as a result of aging tests were performed on tensile investigated steel. The test results have been constructed according to clearly demonstrate the change in mechanical properties, and thus the inclination of the test of rolled metal to aging. It was found that the warranty period for the mechanical properties of high-strength steel grades HX220YD, HC220Y, 006 / IFCR and 006 / IFGR is 6 months. As for the rental of steel grades A341-A5 and HX180BD, hardening during the subsequent drying of the paint, the shelf life of such products must not exceed 3 months. After this period the metal begins to rapidly age and its technological and operating properties deteriorate significantly.

Warranty claim analysis according to good usage policy

Warranty is a term provided by the producer in order to overcome the loss of a company's goodwill if some products fail to perform as expected due to error while in production. In previous works on warranty, it is noted that frequently some products are claimed for warranty due to damage caused by bad usage or lack of knowledge by the user. The cost related to these claims is high and needs to be considered. In this work two models are developed for determining two types of warranty claims using homogeneous Poisson process (HPP), learning rate factor (Chase et al., 1999) and simulation. The two types are fatal failure and intermittent failure of the product. In the last section of the work there is a brief description of a new model which may bring the concept of a variable warranty period of product.

Risk Analyst: A New Player in the Construction Processes – Portugal

In Portugal, the established structure for the construction, does not work in favor of its quality! The construction sector, at the height of its financial strength, from 1980 to 2007, has always had the tendency to skid beyond the initial budgets. It is true that these were drawn up on a stage still under construction, for the sake of time management and to please the Project Owner (P.O.). When transiting to the construction site all was uncovered, and the P.O. had to deal with higher costs and unanticipated. The General Contractor (G.C.) took advantage of this weakness and would rework its proposal - dumping was a current practice, with the certainty of what would happen - what in fact only aggravated the situation. The designers were averse to change and conflicts would arise with the P.O. and G.C.. Given this the only entity considered to be independent, to mediate the situation was the Inspection. This, for its part, took the side of the strong players - P.O. and G.C. - in an attempt to balance the immediate savings of both, leading to systemic build failures with huge impact on the edified, which in turn affected the warranty period. As a rule the G.C. would refuse to do any repair - claiming that she had just built in accordance with the instructions - hiding behind the imposed economy and ignoring the projects - with the consent of the P.O.

Fatigue Life Evaluation of Rubber-Clay Nanocomposites

The interest of fatigue life evaluation for rubber component such as engine mount was increasing according to the extension of warranty period of the automotive components. A design of rubber components against fatigue failure is one of the critical issues to prevent the failures during the operation. Therefore, fatigue life prediction and evaluation are the key technologies to assure the safety and reliability of mechanical rubber components. In this study, we developed rubber material that is environment-friendly and superior in physical property and fatigue life using rubber-clay nanocomposite. We performed static and dynamic tests of rubber-clay nanocomposite synthesized by inserting nano-filler between silicate layers at the high temperature of +70 ˜+100°C, and verified that their mechanical properties were superior to the existing rubber material. In addition, a new method was developed to estimate fatigue lifetime of rubber parts in a short period in the initial stage of design, assuming that the fatigue damage parameter was Green-Lagrange strain generated at the weak points of parts. As results of estimation of fatigue durability, it was verified that the fatigue lifetime obtained by fatigue tests on actual engine mounts and the expected lifetime relatively match. With the results of finite element analysis of rubber parts using the fatigue lifetime estimation method suggested in this study, the lifetime can be estimated without fatigue tests on rubber parts. Therefore, we can save development time and expense and achieve good quality and reliability of rubber parts.

Effect of Price and Brand on Common Platform Appliance Failure

This main objective of this study is to determine if common platform dishwashing products have similar warranty failure rates when brands and price points are variable. Data for this study are based upon over four years of data involving one million individual sales and over 150,000 warranty failures of a common platform dishwashing appliance. It is concluded that there are similar failure rates between common platform dishwashers when different brands are at the same price point. Other conclusions indicate that there are non-similar failure rates between common platform dishwashers when the same brand is at different price points. There is a significant resource cost in the development of products. To minimise the resource cost and maximise the return on investment, many companies develop several new products from one common platform. Common platforms spread across several separate brands. Different brands attract different customers who have different perceptions of quality. Customers view quality as a mix of utility and reliability and expect high reliability during the warranty period. It is often assumed by the developer that the warranty failure rate will be similar for common product platforms even when products are marketed under different price points. The goal of this research is to test if this common assumption is accurate.

Abstract 16212: Warranty Period of Zero Coronary Artery Calcium Score in Asymptomatic Korean Individuals

Introduction: Zero coronary artery calcium (CAC) is a reliable predictor of absent atherosclerosis and serves as a useful adjunct for identifying those at low risk. Despite this, the “warranty period” that displays the protective value associated with the absence of CAC towards experiencing a cardiovascular event among Asians is not well established. Hypothesis: To examine whether the absence of CAC displays a more favorable warranty period for all-cause death compared with the presence of CAC in a Korean cohort. Methods: A total of 48,215 asymptomatic Koreans (mean age: 54±8.8 years; 25% women) were enrolled and stratified by the absence or presence of CAC. Time to exceeding 1% of cumulative all-cause death was estimated in order to identify low-risk individuals. Hazard ratios (HR) with 95% confidence intervals (95% CI) for all-cause death were estimated according to prespecified cardiac risk factors and the presence of CAC. Results: In total, 30,605 (63.5%) individuals presented with a zero CAC. Across a median follow-up of 4.4 years (Interquartile range: 2.7-6.6 years), 415 (0.9%) individuals experienced the endpoint of all-cause death. For those with a zero CAC, the time to exceeding 1% risk was found to be 9 years, indicating a substantially longer warranty period compared with participants with a CAC>0 (e.g., 5 year warranty period). The time to exceeding 1% risk tended to decline for individuals on the background of increasing CAC scores. For each of the other prespecified risk factor groups, a zero CAC provided a longer cumulative event free period than in the presence of any CAC. Cox regression analyses also revealed that the absence of CAC was independently associated with a lower risk of all-cause death in each of the respective risk factor groups when compared with CAC>0. Conclusions: In a large cohort of asymptomatic Korean individuals, the absence of CAC evokes a strong protective effect against all-cause death as demonstrated by a longer warranty period.

Simultaneous settings of order quantity, wholesale price, production run length, process mean, and warranty period

In this article, the authors propose a modified version of S.L. Chen and Liu's model with a two-stage production system. Assume that the retailer's order quantity is concerned with the manufacturer's selling price and the warranty period of product. The used cost of the customer is measured under the Taguchi's quadratic quality loss function and concluded in the retailer's profit function. The quality of the lot for the manufacturer is determined by adopting a two-stage single sampling rectifying inspection plan. The modified economic manufacturing quantity (EMQ) model is addressed in formulating the manufacturer's expected profit. The retailer's order quantity, manufacturer's wholesale price, production run length, process mean, and warranty period of product will be jointly determined by maximizing the total expected profit of the supply chain system including the manufacturer and the retailer. Finally, the quality investment policy is introduced to illustrate the profit improvement for the supply chain system.

Определение возможных неисправностей современных автомобилей в гарантийный период

Определение возможных неисправностей современных автомобилей в гарантийный период

공동주택의 하자진단에 기초한 공종별 하자보수비용의 분석

This study investigated defect status by work type, based on the report data of defect inspection results, acquired by consumers’ request to safety inspection agencies, before the expiration of legal defect repair warranty period. In fact, the data was not acquired by centering on suppliers, namely, construction companies in relation with the defects becoming causes to increase construction cost of apartments. This study aims to provide objective and basic data for quality improvement at construction stage and for solution to defect disputes. The study results are presented below: (1) The number of defect cases occurring from architectural work among total work types were 1,986, defect occurrence rate was 62.5%, and defect repair cost was KRW 25,851/㎡, which stood at 78.2% of the total work types. This means the defect occurrence rate and defect repair cost in architectural work are bigger than those of other work types. (2) Major defects in architectural work were revealed in the following order: cracks from frame work, inferior interior finishing work, inferior finishing work of plaster/masonry works, water leak/damage from waterproof work and withering/omission from landscape work. The total repair cost of the major selected defects was KRW 12,220/㎡, and was analyzed to take up 37% of the total defect repair cost.

OPTIMAL RELEASE TIME DECISION FROM FUZZY MATHEMATICAL PROGRAMMING PERSPECTIVE

Demand for high software reliability requires rigorous testing followed by requirement of robust modeling techniques for software quality prediction. On one side, firms have to steadily manage the reliability by testing it vigorously, the optimal release time determination is their biggest concern. In past many models have been developed and much research has been devoted towards assessment of release time of software. However, majority of the work deals in crisp study. This paper addresses the problem of release time prediction using fuzzy Logic. Here we have formulated a Fuzzy release time problem considering the cost of testing under the impact of warranty period. Results show that fuzzy model has good adaptability.

A 15-Year Warranty Period for Asymptomatic Individuals Without Coronary Artery Calcium: A Prospective Follow-Up of 9,715 Individuals

ObjectivesThe aim of this study was to examine the long-term prognosis in asymptomatic individuals with a coronary artery calcium (CAC) score of 0 and its associated warranty period. BackgroundEmerging evidence supports a CAC score of 0 as a favorable cardiovascular short-to intermediate-term prognostic factor. MethodsA total of 9,715 individuals undergoing CAC imaging were stratified by age, Framingham risk score (FRS), and National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) categories and followed for a mean of 14.6 years (range 12.9 to 16.8 years). Cox regression, area under the receiver-operating characteristic curve, and net reclassification information were used to assess all-cause mortality, discrimination, and reclassification of a CAC score of 0 compared with the FRS and NCEP ATP III, respectively. A warranty period was pre-defined as <1% annual mortality rate. Vascular age was estimated by linear regression. ResultsIn 4,864 individuals with a baseline CAC score of 0 (mean age, 52.1 ± 10.8 years; 57.9% male), 229 deaths occurred. The warranty period of a CAC score of 0 was almost 15 years for individuals at low and intermediate risk with no significant differences regarding age and sex. A CAC score of 0 was associated with a vascular age of 1, 10, 20, and 30 years less than the chronological age of individuals between 50 and 59, 60 and 69, 70 and 79, and 80 years of age and older, respectively. The CAC score was the strongest predictor of death (hazard ratio: 2.67, 95% confidence interval: 2.29 to 3.11) that enabled discrimination and consistent reclassification beyond the FRS (area under the receiver-operating characteristic curve: 0.71 vs. 0.64, p < 0.001) and NCEP ATP III (area under the receiver-operating characteristic curve: 0.72 vs. 0.64, p < 0.001). ConclusionsA CAC score of 0 confers a 15-year warranty period against mortality in individuals at low to intermediate risk that is unaffected by age or sex. Furthermore, in individuals considered at high risk by clinical risk scores, a CAC score of 0 confers better survival than in individuals at low to intermediate risk but with any CAC score.

Оптимальні методи оцінки білкових помутнінь ігристих вин

Colloidal blur is the most common and intractable feature for white sparkling wines. Violation of the equilibrium state of the colloidal nature of the components under the external factors influence (temperature, light, vibration, etc.) leads to formation of large particles, blur and sedimentation development. These changes are predetermined by the presence of macromolecular materials and substances of grape and yeast origin in sparkling wines (i. e. proteins, polysaccharides, phenolic substances). Today there is a wide range of tests predicting protein blur, which are widely used in winemaking practices to determine stability of sparkling wines. The comparative characteristics to thermal and combined chemical tests as well as instrumental methods for determining protein casse, is given in the article due to the one presented in domestic and foreign literature. The results of comparative evaluation of proteins detection effectiveness for white sparkling wines are presented. It is indicated that the blur values of the test samples are different for proteins in each test group. It was set that thermal tests are little-informative and give an idea of the heat-labile proteins. Thermal tannin test group shows the highest level of correlation between the test value and the one for the storage warranty period. Tests with TCA did not reveal any correlation between blur values and sparkling wines’ stability.

Optimal Two Dimensional Preventive Maintenance Policy Based on Asymmetric Copula Function

For some kinds of products, the consumers have strict requirements to the reliability of these products in the based warranty period. Then the manufacturer is inclined to provide the two-dimensional preventive maintenance policy to take the usage degree of the product into account. As a result, two-dimensional preventive maintenance policy in the warranty period has recently obtained increasing attention from manufacturers and consumers. In this paper, we focused on the optimization of based warranty cost and proposed a new expected based warranty cost model considering the two-dimensional imperfect preventive maintenance policy from the perspective of the manufacture. Asymmetric copula function was applied to modeling the failure function of the product. And the optimal two-dimensional preventive maintenance period was obtained by minimizing based warranty cost. At last, numerical examples are given to illustrate the proposed models, of which the results prove the model effective and validate.

Optimum Time-Censored Modified Ramp-Stress ALT for the Burr Type XII Distribution with Warranty: A Goal Programming Approach

Accelerated life tests (ALTs) are used to make timely assessments of the life time distribution of highly reliable materials and components. Much of the previous work on ALTs has focused on constant-stress, step-stress, ramp-stress schemes and their various combinations. In the literature ramp-stress ALTs that have been formulated can be conducted when more than one test chambers are available; installation of which may prove to be costly. Even when one test chamber is used the stress rate remains constant throughout the duration of the experiment. It is not only necessary but imperative to examine if the test specimen is able to withstand differing stress conditions with the passage of time. This paper therefore, presents an optimal design of multi-objective modified ramp-stress ALT model with weighted goal programming approach. The modified ramp-stress uses one test chamber in place of the various chambers used in simple ramp-stress ALT thus saving experimental cost. With the market being increasingly competitive the emphasis today is on goal attainment with minimum deviations. Goal programming is a method to solve multi-objective problems that has applications in varied fields of engineering and operational research. The optimal plan consists in finding out relevant experimental variables, namely, stress rate, stress rate change point and warranty period, by using goal programming on weighted sum of variance of reliability function and expected warranty cost with pre-specified mission time under normal operating conditions. The Burr type XII life distribution and time-censored data have been used for the purpose. Burr type XII life distribution has been found appropriate for accelerated life testing experiments. The method developed has been explained using a numerical example and sensitivity analysis carried out. Comparative study has also been done to highlight the merits of the proposed model.

A 15-YEAR WARRANTY PERIOD FOR ASYMPTOMATIC INDIVIDUALS WITHOUT CORONARY ARTERY CALCIUM: A PROSPECTIVE FOLLOW-UP OF 9,715 INDIVIDUALS

A zero coronary artery calcium (CAC) score reflects a favorable near-term prognosis. However, the long-term “warranty period” of a CAC=0 is relatively unknown. A total of 9,715 asymptomatic individuals undergoing CAC scoring were followed for a mean duration of 14.6±1.1 years. Cox proportional

Designing the Optimal Extended Warranty Price with Indirect Network Effect

AbstractIn the situation of indirect network effect, this paper mainly studies the optimal extended warranty price. First, the characteristics of the extended warranty price are discussed. Next, the optimal extended warranty price model is advanced. From the model, the authors can draw that the influence factors mainly include the producer and consumers’ risk preferences, the incompatible degree of the producer’s maintenance technology, the extended warranty period, the producer and consumers’ per-occasion maintenance cost. Finally, the authors carry the simulation method to indicate their influence relation. The results have theoretical significance for the automobile producer to ensure the optimal extended warranty price.

Warranty periods for normal myocardial perfusion stress SPECT

BackgroundTo assess different warranty periods following a normal myocardial perfusion SPECT based on patients’ clinical characteristics and the type of stress performed. Methods and ResultsA study was done of 2,922 consecutive patients (62.9 ± 13 years; 53.4% women) with a normal stress-rest SPECT. The warranty period was defined as the period during which patients remained at a low risk (<1% events/year) of total mortality (TM), or hard events (HE) (cardiac death or non-fatal myocardial infarction). Of these patients, 2,051 were given an exercise myocardial perfusion imaging (Ex-MPI); 461 submaximal exercise plus dipyridamole (Ex+Dipy-MPI); and 410 dipyridamole (Dipy-MPI). During a mean follow-up of 5 ± 3.3 years, a significant reduction (P < .05) of the warranty period for TM (13.5, 9.6 and 8 months) and HE (34.8, 20.5 and 8.2 months) was observed, for Ex-MPI, Ex+Dipy-MPI and Dipy-MPI, respectively. Other warranty period determinants were the clinical variables of age, sex, diabetes and known coronary artery disease. An abnormal left ventricular ejection fraction on gated-SPECT also significantly shortened the warranty period for HE in patients undergoing Ex+Dipy-MPI (P = .001) or Dipy-MPI alone (P = .007). ConclusionsThe warranty period for a normal stress-rest SPECT is highly variable since it is primarily determined by the type of stress, the patient’s clinical characteristics and LVEF.

Optimal Warranty Policy Considering Two-dimensional Imperfect Preventive Maintenance for Repairable Product

For some kinds of products, such as car, aircraft, government acquisition, the consumers have strict requirements to the reliability of these products. Then the manufacturer is inclined to provide the two-dimensional preventive maintenance policy to take the usage degree of the product into account. As a result, two-dimensional preventive maintenance policy in the warranty period has recently obtained increasing attention from manufacturers and consumers. In this paper, we focused on the optimization of based warranty cost and proposed a new expected cost model of the two-dimensional imperfect preventive maintenance policy from the perspective of the manufacture. The optimal two-dimensional preventive maintenance was obtained by minimizing based warranty cost. And asymmetric copula function was applied to modeling the failure function of the product. At last, numerical examples are given to illustrate the proposed models, of which the results prove the model effective and validate. DOI: http://dx.doi.org/10.11591/telkomnika.v13i2.7043 Full Text: PDF