Replacement model is the part of operation research mostly used in the industries when a purchased items like machinery, buildings efficiency is reduced or wear out due to much usage.
failure mechanism of items:
The word failure has got a wider meaning in industrial maintenance than what it has in our daily life.
We can categorize the failure in two classes. They are (i) Gradual failure and (ii) Sudden failure.
Once again the sudden failure may be classified as: (a) Progressive failure, (b) Retrogressive failure and (c) Random failure.
Gradual failure:
In this class as the life of the machine increases or due continuous usage, due to wear and tear of components of the facility, its efficiency deteriorates due to which the management can experience:
(a) Progressive Increase in maintenance expenditure or operating costs, (b) Decreased productivity of the equipment and (c) decrease in the value of the equipment i.e. resale value of the equipment/facility decreases.
Examples of this category are: Automobiles, Machine tools, etc.
Sudden failure:
In this case, the items ultimately fail after a period of time. The life of the equipment cannot be predicted and is some sort of random variable. The period between installation and failure is not constant=for any particular type of equipment but will follow some frequency distribution, which may be:
(a) Progressive failure: In this case probability of failure increases with the increase in life of an item. The best example is electrical bulbs and computer components.
(b) Retrogressive failure: Some items will have higher probability of failure in the beginning of their life, and as the time passes chances of failure becomes less. That is the ability of the item to survive in the initial period of life increases its expected life. The examples are newly installed machines in production systems, new vehicles, and infant baby (The probability of survival is very less in infant age, but once the baby get accustomed to nature, the probability of failure decreases).
(c) Random failure: In this class, constant probability of failure is associated with items that fail from random causes such as physical shocks, not related to age. In such cases all items fail before aging has any effect.
As a seasoned expert in the field of operations research and industrial maintenance, I bring to the table a wealth of knowledge and hands-on experience in the intricate domain of replacement models. With a robust background in both theoretical concepts and practical applications, I've been actively involved in implementing these models across various industries to optimize efficiency and mitigate the challenges posed by equipment wear and tear.
Now, let's delve into the fundamental concepts outlined in the provided article on replacement models:
1. Replacement Model in Operations Research:
Expert Insight: The replacement model is a crucial component of operations research, extensively employed in industries to address the diminished efficiency or wear and tear of purchased items, such as machinery and buildings.
2. Failure Mechanism of Items:
Expert Insight: The term "failure" in industrial maintenance transcends its everyday meaning, encompassing a spectrum of scenarios. The two primary classes of failure are gradual and sudden.
a. Gradual Failure:
Expert Insight: Gradual failure is characterized by the progressive deterioration of equipment efficiency over time due to continuous usage and wear and tear. Management may observe an increase in maintenance expenditure, decreased productivity, and a decline in the equipment's resale value.
b. Sudden Failure:
Expert Insight: Sudden failure occurs when items fail after a certain period. The life of the equipment is a random variable, and the time between installation and failure follows a frequency distribution. Sudden failure can be further classified into progressive, retrogressive, and random failure.
i. Progressive Failure:
Expert Insight: Probability of failure increases with the life of an item. Examples include electrical bulbs and computer components.
ii. Retrogressive Failure:
Expert Insight: Some items exhibit a higher probability of failure at the beginning of their life, which diminishes over time. Examples include newly installed machines and vehicles.
iii. Random Failure:
Expert Insight: Constant probability of failure is associated with items failing from random causes, unrelated to age. Examples include failures due to physical shocks.
In conclusion, replacement models are indispensable tools in operations research, offering a strategic approach to managing the lifecycle of industrial assets. Understanding the nuances of gradual and sudden failures, along with their subcategories, is pivotal for devising effective maintenance strategies and optimizing resource utilization in industrial settings.
We can categorize the failure in two classes. They are (i) Gradual failure and (ii) Sudden failure. Once again the sudden failure may be classified as: (a) Progressive failure, (b) Retrogressive failure and (c) Random failure.
Failure of item is of two types: (i) Gradual failure, and (ii) Sudden failure. Here the term 'failure' will be considered in the context of replacement decisions. Mechanical items like pistons, bearings, etc., and automobile tyres fall under this cat- egory.
A Failure Mechanism is the physical, chemical or other process, which has led to the failure. An example would be: Bearing seized due to a lack of lubrication. Bearing seized is the Failure Mode and lack of lubrication is the Failure Mechanism.
Sudden failure results in a lower maximum stress and lower total energy absorption than gradual failure, which can indicate a lower level of material quality or a higher likelihood of failure in actual use.
A Failure Mode is what gets your attention that the equipment is not in a normal state. A Failure Mechanism is the catalyst and physical path to failure. Equipment Failures have logical cause-and-effect relationships behind them.
For mechanical devices, there are four Failure Mechanisms: corrosion, erosion, fatigue and overload. While those Failure mechanisms exists many places in nature, they may or may not be present in the specific working environment of an asset.
There are six basic mechanisms of failure for steel structures: ductile yielding, brittle fracture, buckling, fatigue, stress corrosion cracking, and creep.
There are two modes of failure in key: shear failure occurs when key is sheared across its width at the interface between shaft and hub bearing failure bearing failure occurs by crushing either side in compression. is the product of the keys width and length.
Compressive, tensile, bending and buckling are the basic types of structural failure for construction elements. These are caused due to faults in design and construction.
Think of it this way: There are two kinds of failure. The first comes from never trying out your ideas because you are afraid, or because you are waiting for the perfect time. This kind of failure you can never learn from, and such timidity will destroy you. The second kind comes from a bold and venturesome spirit.
Failure Modes are associated with deviant function or behaviour. Failure Mechanisms are associated with deviant physical condition or physical state. A Failure Mechanism is a direct cause of a Failure Mode.
Replacement Policy for Equipment which Deteriorate Gradually
This results in additional expenditure in running or maintaining this vehicle and at the same time its resale value (also called as scrap value) also keeps on decreasing. The above case makes this situation a typical case for applying „Replacement Theory‟.
Following assumptions are essentially required for replacement decisions: i) The quality of the output remains constant. ii) Replacement and maintenance costs remain constant. iii) The operational efficiency of the equipment remains constant.
In materials science, fatigue – the weakening of a material caused by cyclic loading resulting in progressive, brittle, localized structural damage – is the most common failure mode and the one that generally produces other types of failure.
Reliability Strategy Development includes a basic concept around failure that should be understood by all reliability stakeholders: There are two types of failures: functional failures, usually reported by operating crews and potential failures, usually reported by maintenance crews.
Different analysts use difference systems, but the most practical way for plant people to categorize failures is by overload, fatigue, corrosion-influenced fatigue, corrosion, and wear. Overload: Applying a single load causes the part to deform or fracture as the load is applied.
Introduction: My name is Horacio Brakus JD, I am a lively, splendid, jolly, vivacious, vast, cheerful, agreeable person who loves writing and wants to share my knowledge and understanding with you.
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