The purpose of this study is to develop a more realistic cumulative damage replacement framework for systems subjected to shocks and prior wear. Existing models assume new equipment with no residual degradation, which can misguide maintenance decisions for fairly- used machinery common in developing economies. This study incorporates initial damage and a shock-dampening factor to capture reduced vulnerability to shocks. It evaluates age-based, shock-based, damage-based and joint replacement policies using an industrial washing machine, with the goal of identifying cost-effective strategies and improving maintenance planning for partially worn, shock-resistant systems.
A modified cumulative damage model is proposed, incorporating two key factors: initial residual damage and shock-dampening factor that attenuates the impact of external shocks. Three practical single replacement policies: age-based, shock-count-based and damage-threshold-based are formulated and analytically evaluated. Furthermore, a joint criteria maintenance model is developed that provides the jointly optimal result for any fairly used and new machines. These models are applied to an industrial washing machine case study to compare the cost performance of each policy and a unified joint policy.
The modified cumulative damage model incorporating prior wear and shock dampening accurately predicts optimal replacement decisions for fairly- used systems. For the industrial washing machine, optimal single-policy decisions occur at 400 h, 8 shocks and 700 damage units, with the age-based strategy yielding the lowest cost. The joint policy identifies an optimal solution at 450 h, 8 shocks and 800 damage units, achieving a lower overall cost than the combined single-policy costs. Compared with the baseline model assuming no prior damage or shock resistance, the proposed framework provides more realistic replacement intervals and avoids misleading maintenance delays.
The study assumes constant shock-arrival behaviour and a fixed shock-dampening factor, which may not fully capture machines operating in highly variable environments. Parameter estimation relies on external data, limiting precision where local data are unavailable. The model focuses on non-repairable systems and may require adaptation for partially repairable assets. Future work should incorporate dynamic shock resistance, variable operating conditions and improved field data collection to enhance accuracy. These extensions would expand applicability across diverse industrial settings and strengthen the generalizability of cumulative damage-based maintenance policies.
The proposed policies provide maintenance managers with realistic replacement intervals for fairly- used machinery, preventing premature failure and reducing unplanned downtime. By integrating prior wear and shock attenuation, it supports more accurate lifecycle cost estimation and improves planning for second-hand equipment common in resource-constrained economies. The joint policy helps avoid redundant replacements, offering a more economical strategy than single-criterion approaches. Overall, the model strengthens decision-making for preventive replacement, enhances equipment availability and reduces long-term operational costs.
Improved maintenance planning for fairly- used machinery supports operational continuity in developing economies where second-hand equipment is widely used. By reducing unexpected failures, downtime and repair expenses, the model contributes to safer work environments and more reliable service delivery in sectors such as manufacturing, healthcare and utilities. Cost-effective replacement strategies can also lower the financial burden on small and medium enterprises, promoting economic resilience. The approach ultimately enhances productivity and supports sustainable equipment use in resource-limited settings.
This study introduces a generalized cumulative damage framework that, for the first time, explicitly incorporates both residual wear and shock-dampening behaviour into replacement modelling for fairly- used systems. It extends traditional models by enabling simultaneous evaluation of age, shock count and cumulative damage through a joint policy that minimizes redundant replacements. The model unifies cases for new and used equipment, reducing to existing formulations when no prior damage or shock resistance is present. Its ability to capture realistic degradation mechanisms offers significant value for maintenance engineering, especially in contexts dominated by second-hand machinery.
