Designing For Reliability

Designing for reliability is a fundamental aspect of engineering that focuses on creating products, systems, and structures that can consistently perform their intended functions over an extended period without failure. Reliability is a crucial consideration in various industries, including aerospace, automotive, electronics, energy, and manufacturing.

If a product’s parts or connections wear out after typical use, the product will no longer perform as expected and will need to be replaced. Determining what factors lead to material deterioration is the topic of this article. Components are what I’ll use for simplicity, but joints are what we’re really talking about here.

Materials and Dependability

Exposure to use conditions might cause the materials used in a product to deteriorate. Certain plastics grow brittle when exposed to sunshine, and steel screws corrode when submerged in water. Fatigue, creep, wear, corrosion, and embrittlement are only a few of the degrading mechanisms that can occur in mechanical parts. Degradation mechanisms for electrical components include electromigration and dielectric breakdown.

Deterioration causes materials and components to lose functionality. Degradation beyond a certain threshold causes the part to stop doing its job. If this causes a product to degrade or stop working before its designated end of life, it is a serious issue.

So, the degree to which the materials that make up a product degrade affects how reliable that product is. Choosing materials that can survive the conditions to which they will be exposed is an important component of designing products with high reliability.

The rest of this article will go through methods for determining the sources of stresses on parts and connections.

Stressors

A component’s environmental circumstances include stresses exerted on the materials during processing, transport, and use. A stressor could be…

• Static, cyclic, or impact loading; abrasion; and rubbing are all examples of mechanical forces.
• Electromagnetic, including current, voltage, or UV exposure
• heat-related, including but not limited to, high temperatures and temperature swings
• Having to do with chemistry, such gasses, solvents, acids, or bases,
• substances found in living organisms,
• Having an electrochemical nature when subjected to corrosion

Causes of Tension

The five main causes of stress are as follows:

• Functionality of Parts
• Environment
• Connections to other elements
• Abuse of a minor nature
• Misuse.

The stresses placed on a component are directly proportional to its functionality. Mechanical loads on a motor shaft, while the shaft is used to move another device and electrical current in a circuit, are two examples. If the mechanical loads on the motor shaft are cyclical, this might result in the development of a fatigue crack that eventually leads to the shaft breaking. Electromigration can be caused by the current in a circuit and result in an open circuit.

The term “environment” is used to describe the setting in which a certain component functions. Stressors in the environment include things like

Substances that, when in contact with processing plant machinery, might cause corrosion. Conditions of extreme heat can degrade polymers and trigger phase changes in metals. Many products have different environmental requirements for different parts of the product. Unlike the engine compartment, the passenger area of a car is not subjected to the same high temperatures and humidity that might cause corrosion. When compared to the handle, a skillet’s pan experiences substantially higher cooking temperatures.

Components interact with one another when they come into physical touch or when one component outgases a chemical that interacts with another. The following are some examples of interactions between physically touching parts:

• Friction and wear between gears.
• Corrosion is caused by an electrical current when two dissimilar metals come into contact.
• Component-to-component stresses are caused by dissimilar thermal expansion rates of their constituent materials.
• Wear, rolling contact fatigue, crevice corrosion, heating, outgassed chemicals, and other stresses are all examples of interactions.

Mild abuse describes stresses that are slightly above what would be considered normal during normal use. Dropping a phone from a short height onto concrete, driving through potholes, and spilling a small amount of chemicals on a motor all qualify as examples of light abuse. Many items must be able to take minimal amounts of damage before they cease functioning as intended.

Misuse is any form of stress that goes beyond what would be considered normal. Goods are not required to be built to endure mistreatment. You can’t expect a phone to keep working after you drop it in the toilet or use it to bang a nail into the wall. Like hoping your automobile would continue to work after you drive it through two feet of water.

Quantify the Effects of Stressors

The next step, after identifying the sources of strain, is to quantify them. Either direct measurement or modeling can do this.

Another method is to make educated guesses, but this has its own drawbacks. If you guess too low, certain of your parts won’t have the durability your product requires. If two things hold true, then this method might be fine. Secondly, iterating component designs until they pass testing is only effective when reliability testing is also used. Second, if the testing and redesign iterations are given adequate time and resources throughout product development.

Overestimating the dependability requirements could result in higher component costs. If this method ensures that the product passes reliability testing the first time around, eliminating the need for redesigns, and allowing the product to be released on schedule or ahead of schedule, then it may be acceptable.

The benefits of guessing include the time and resources avoided in determining the exact size of the stressors.

Nothing left to chance

In order to design components with the required reliability, it is essential to first identify all the stresses operating on the component. This data is essential for determining the best shape and materials for each component. To ensure the materials are fit for purpose, it is also required to create product dependability testing.

Understanding the components’ intended function and the environmental conditions to which they will be subjected is essential for the stressor identification procedure. When it comes to pinpointing the parts of a project that absolutely must not fail, FMEA is an invaluable resource. A materials engineer’s input will be useful here.

Uncertainty in the design process is stressful because it results from not identifying all the stressors and their magnitudes early in product development. When more time passes and more decisions must be made, the pressure mounts.