Journal of Quality Engineering and Management

Abstract Purpose: This study aims to optimize warranty periods for complex products by examining the role of warranties in customer retention and cost management. The proposed model uses a mixed statistical distribution to simultaneously model minor and major failures, seeking to minimize the product's life-cycle cost while maintaining customer satisfaction.
Methodology: The mathematical model defines life-cycle costs, establishes an objective function to minimize total costs, and determines the optimal warranty period. A numerical example and sensitivity analysis are used for validation, and the model is solved using Maple 2024.
Findings: The optimal warranty period was identified as 3.5-4.5 time units, and the model achieved a 23% cost reduction compared to conventional methods. Sensitivity analysis showed that changes in failure probability and failure rate directly affect the optimal warranty length.
Originality/Value: Using a mixed statistical distribution to model different failure types simultaneously offers an innovative, more realistic approach. This model provides a practical tool for adjusting warranty policies and reducing life-cycle costs, with potential for further development by incorporating dependent failures and real-world data.

Abstract Purpose: Calculating the optimal target mean for a process is recognized as an essential research area, with many proposed models in the literature. Previous studies have typically focused on a single market. The main difference in this research lies in the number of markets considered; unlike previous works, this study examines n different markets simultaneously.
Methodology: This study aims to determine the optimal process quality mean for a limited number of markets based on the target values of quality characteristics in each market. We propose a model to calculate this optimal mean across n markets with different price/cost structures. A key innovation of this research is the incorporation of probability distributions that reflect the likelihood of the quality characteristic falling within specific quality ranges in each market.
Findings: The model considers the probability that the quality characteristic falls within each market's defined quality range. To analyze and solve the model, absorbing Markov chains are used. A numerical example is presented in which the model is applied to two markets, and the optimal target mean and corresponding optimal revenue are obtained.
Originality/Value: Based on the results from the numerical example, the optimal target mean and revenue were determined for the two markets. A sensitivity analysis was conducted to assess the influence of various model parameters on these parameters, demonstrating how changes in parameters impact the model's outcomes.

Abstract Purpose: The goal of this research is to establish a design framework based on reliability for submarine pressure hulls, with the aim of attaining an ideal equilibrium between structural integrity and reliability.
Methodology: Initially, a mechanical Finite Element Model (FEM) was created and verified by comparing it to experimental data. Following that, various alternative models created through weight optimization algorithms were formulated. Uncertainties were represented using random variables, and reliability assessments were performed for each design.
Findings: The findings suggest that optimized models, even with reduced weights, can provide satisfactory failure probabilities. The prioritization derived from the reliability analysis offers a clear view of the final design.
Originality/Value: This study's uniqueness stems from its combined application of finite element analysis, uncertainty modeling, and optimization methods in reliability-based pressure hull design, a strategy seldom utilized in marine structural design.

Abstract The Permasin engine is a critical mission-oriented system, the failure of which will cause the failure of the main mission. Comprehensive studies on its reliability can be a step towards improving the performance of this system. The aim of the article is to analyze the reliability of the Permasin engine in the specified scenarios. In this article, first of all, the structure of Permasin engine as the studied system is described and the breakdown structure of the product is drawn for this system, and according to the mission-oriented nature of this system, there are 2 time scenarios, the basis of floating performance, definition and failure rate for sensitive parts from the standard. MilHDB-217 and NPRD-95 will be calculated in two optimistic and pessimistic modes. By using the breakdown structure, the connection of specific system components and the reliability block diagram are drawn in the Reliability Workbench software. Finally, the reliability of the subsystems and the studied system is calculated separately for both working scenarios. The results show that drive and motor subsystem has the lowest level of reliability compared to other subsystems in rated power.