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Title: What types of testing occur within a materials testing laboratory?

Author for citation: Shawn E. Douglas

License for content: [* https://creativecommons.org/licenses/by-sa/4.0/ Creative Commons Attribution-ShareAlike 4.0 International]

Publication date: November 2023

Materials testing: The basics

Materials science and its associated tests are largely considered a part of the applied science branch of sciences, as the study and testing of the properties of materials are put to use in the manufacture and construction of a wide variety of items. Testing methodologies can be divided into physical, mechanical, chemical, and biological property testing, with each test falling under the category of destructive or non-destructive. Testing of a material may involve one or more of these methodologies, and occasionally all of them may be used as part of a comprehensive analytical approach towards a material.

Material testing may happen under the umbrella of materials discovery and research, or materials quality/suitability testing. In the case of the former, computational methods may initially be used to search through existing materials databases, as well as virtually develop new material models for potential real-life development, before any actual real-world materials testing begins. In the case of the latter, the material is already discovered or created, and materials testing occurs to verify that its properties are suitable or of sufficient quality for their intended purpose. Technological systems such as laboratory information management systems (LIMS) may be used in both cases to better manage the associated data and information coming from their materials science activities.

Materials testing is as diverse as the available material types and industrial applications of those material types. Material testing domains include:

• Aerospace
• Automotive
• Carbon
• Coatings, linings, and sealants
• Construction and engineering
• Insulation, foam, and composites
• Lubricants and thickeners
• Medical devices
• Metals
• Packaging and labeling
• Paints and oils
• Paper
• Polymers and plastics
• Raw materials
• Reference materials
• Rubbers
• Electronics and energy devices
• Textiles
• Wood

Optimally, materials testing is performed by a laboratory that is accredited to a relevant set of standards and test methods, making materials testing more standardized and reliable, in turn adding confidence to any items made or constructed from those tested materials.

Materials testing types

As noted prior, the diversity in materials testing methods is immense. As such, it's difficult to address all of them in an FAQ. That said, this article will provide examples of destructive and non-destructive test methods across the four property testing categories: physical, mechanical, chemical, and biological. (Note that in a few cases, a test might be destructive or non-destructive, depending on the particulars, for example as found with hardness, thickness, and crimp (length) testing, which are physical tests. However, also note that physical tests aren't commonly destructive.) Real-world examples from materials testing laboratories accredited to ISO/IEC 17025 are used to exemplify the broad set of test methods in use.

Physical

A physical property of a material represents the actual physical, inconstant state of the material, with its own set of measurable and observable properties, separate from the material's chemical composition, mechanical, and biological properties.

Non-destructive physical tests include:

• visual testing
• magnetic particle testing
• resonant ultrasound testing
• color tolerance and difference
• specular gloss
• solar reflectance index
• apparent density
• water vapor transmission
• ultrasonic defect testing
• thermogravimetric analysis
• infrared thermography
• airflow resistance

Tests that can be both destructive and non-destructive physical tests include:

• hardness
• dry film and other coating thickness
• yarn crimp percentage (length)

Mechanical

A mechanical property of a material represents the functional, inconstant state of the material, particularly in how it reacts when a load is applied to it. Measuring mechanical properties gives a better idea of the materials realistic service life or performance under mechanical stresses. Mechanical testing is often destructive in nature.

Destructive mechanical tests include:

• scratch adhesion testing
• flattening testing
• flaring testing
• burst strength
• tear strength
• peel strength
• bend testing
• tensile bond testing
• concentrated impact
• compressive resistance
• abrasion resistance

Chemical

A chemical property of a material represents how the material reacts under the duress of outward pressures, which fundamentally change the material into a different material over a period of time.

Destructive chemical tests include:

• corrosion resistance
• flammability
• galvanized coating weight
• leaching

Non-destructive chemical tests include:

• liquid dye penetration https://www.hbbwinc.com/what-we-do/non-destructive-examination/
• chemical composition through spectrometry, spectroscopy, or X-ray fluorescence
• surface tension
• temperature-compensated viscosity

Biological

In the scope of testing quality and suitability of raw materials, a biological property of a material represents how the material reacts to one or more aspects of a biological organism, or how a biological organism reacts to the introduction of the material. Examples of biological properties include:

• toxicity, "the degree to which a material may permanently destroy or impair any part of biological organism;
• bioinertness, the ability of some material to go unchanged and elicit biological activity upon introduction to a biological organism; and
• bioactivity, the ability of a material to "elicit or modulate a favorable response" from one or more systems of a biological organism.

One school of thought has that in vitro testing of biological samples is non-destructive (as with bacterial endotoxins testing). However, one might argue that in some cases the in vitro biological sample being tested must be altered destructively, or even that microbes are living biological entities, which may get destroyed in specific bioburden test types. As such, these tests' classification as "destructive" or "non-destructive" may be viewed with some skepticism.

Destructive biological tests include<:

• bioburden testing
• antimicrobial effectiveness
• microbial immersion

Non-destructive biological tests include:

• bacterial endotoxin testing
• sterility testing
• cell and tissue characterization using ultrasound
• bioburden testing