Destructive testing is done to understand the performance or material behavior of a sample, this procedure is performed to failure of the test sample. Destructive testing procedures can either follow specific standards or be designed to reproduce set conditions of service.
Need of Destructive Testing
Materials undergoing destructive testing are damaged by the test procedure. Still, there are many legitimate use cases for destructive testing. Oftentimes, destructive testing and the use of materials of specific properties come as a regulatory requirement.
The reality is that machines and materials have physical and chemical properties that are not suitable for all situations. For example, metals that rust easily are not suitable for use in highly humid environments.
Even large consumer companies like Apple fall victim to paying little attention to testing the durability of their product designs. The Bendgate scandal, where the iPhone 6 and 6s were prone to bending in tight pockets, was caused by apparent oversights and faulty bend tests by their engineers or contractors.
Types of destructive testing
1. Aggressive environment testing
This includes fracture and fatigue testing in sour (H2S), sweet (CO2), and other corrosive environments. over a range of temperatures and pressures. These tests allow the industry to evaluate the effects of these conditions on materials and performance.
2. Corrosion testing
Metals are widely used in many industries due to their tensile strength and versatility. However, they are also prone to corrosion. Common examples of corrosion are rust on iron-based materials, tarnish on silver, and patina on copper and copper alloys. This is a problem because corrosion reduces the tensile strength and life of these metals.
Corrosion testing is a test method used to evaluate the effectiveness of applied corrosion resistance measures. It covers all practices and processes to prevent or reduce corrosion-related problems. Measurement of properties and corrosion rates can also be considered as part of corrosion testing.
The American Society for Testing and Materials (ASTM International) has an extensive set of standards and test methods for corrosion in various metals and environments. Custom protocols can be developed if required.
3. Fracture and Mechanical Testing
It includes various types of destructive testing methods such as tension test, bend test, Charpy impact test, Pelini drop weight testing, peel test, crush testing, and pressure, and fracture testing. In addition to testing metals, fracture and mechanical tests can be performed on a variety of materials, such as welded polymers including plastic pipes.
4. Fatigue testing
Conducted in air or seawater environments, these tests are used to evaluate the endurance of parent materials and welded joints under constant or variable amplitude loading. This destructive testing method can also be used to test welds, base metals, and heat-affected zones for fatigue crack growth.
5. Hydrogen testing
This type of testing covers materials that are at risk of corrosion from exposure to hydrogen. These tests can be performed at different temperatures and strain rates.
6. Measurement of Residual Stress
Residual stresses are those that remain in a solid material after removing any original causes of stress. These can be intentional, such as with the scratch-resistant glass on smartphones, or unintentional which can lead to premature failure of the structure. Residual stress measurements allow designers and engineers to determine factors such as near-surface and through-thickness residual stress distribution, which can be used in critical engineering assessments.
7. Software Testing
Software testing is performed by software engineers who investigate the quality of software, find failures, and understand risks before the product is suitable for use.
Who Performs Destructive Testing?
Destructive testing can be done internally or with the help of external testing services.
A specialized organization such as NASA will conduct destructive testing within its own facilities. Other companies may hire external content testing facilities. Material testing service providers can perform destructive testing on behalf of OEMs to check if components can function within the required parameters.
Such facilitation skills can also be used to select the material in the first place. Materials testing laboratories have an array of materials whose physical properties are tested and recorded. Materials with desired physical properties can be selected from their combinations. In the US, Nadcap-certified material testing laboratories can be used to perform destructive testing.
Destructive-testing is done by specialized researchers, scientists, and technicians. Who conducts it is determined by the type of destructive testing. In general, destructive testing is done:
- Materials scientists
- Metallurgical and Polymer Engineers
- Specialists in chemistry and electrochemical processes
- Failure Analysis Specialists
- Quality Control Analyst
- Regulatory compliance specialists
This is not an exhaustive list, but it gives a good idea of the purpose of testing as well as the skills required to perform the process.
Difference between Destructive and Non-destructive Testing
Destructive testing is done by damaging the sample being tested. In contrast, during non-destructive testing (NDT), the tested item is not physically damaged and can be used in active operation after testing.
The following table shows the main differences between destructive and non-destructive testing.
In reviewing these differences, keep in mind that destructive and non-destructive testing are generally used for different purposes. Although destructive testing can be used for failure analysis, it focuses on ensuring product quality prior to mass production.
Non-destructive tests are performed on components that look for early signs of degradation and prevent equipment failure. They help maintenance teams conduct condition-based maintenance and predictive maintenance.
Destructive Testing is Essential for Machine Reliability
The reliability of the machine is highly dependent on the quality of the components used. An asset is only as strong as its weakest link. Destructive testing ensures that only components with proper physical properties end up in their machines.
The right materials and good product design are the hallmarks of a quality item – whether it’s a consumer product or an industrial machine.
The results of extensive destructive-testing are important to both equipment manufacturers and the maintenance teams that have to maintain them. After all, these results are also used to determine things like operating characteristics, replacement cycles, maintenance requirements, recommended lifetimes, etc.
Even the best quality items are eventually subject to regular wear and tear and abuse. Maintenance professionals can use NDT inspections to monitor the actual condition of their assets.
In this sense, both nondestructive and destructive testing methods contribute to equipment reliability, although they are used at different points in the equipment life cycle.