Mechanical Testing Methods

Mechanical testing aims to describe the behavior of different materials or components, e.g. syringes, springs, micromotors or microwires under specific loading conditions. It provides information about the relationship between forces and the deformation that results from those forces acting on the components.

There are many standardized mechanical testing methods. The most used are: tensile testing, compression testing, flexural testing, peel testing, shear testing, tear testing, fatigue testing, creep testing and friction testing.

A Universal Testing Machine (UTM) is a device designed to test the mechanical properties of materials, components and products. It can perform many of the aforementioned standardized mechanical testing methods. This versatility is why it is referred to as ‘universal’.  

Most parts and components in different size scales can be tested in universal testing machines as long as the force/torque and deflection necessary for the respective test can be achieved in the instrument and the component can be properly fixed. 

UTMs are used in many industries (e.g. automotive, aerospace, electronics, packaging and biomedical) to make sure materials and final products meet the required specifications. They usually adhere to a series of standards (ISO, ASTM …) so consistency is achieved between test results, also regarding devices from different manufacturers, and so they can be used during several stages of product development.

UTMs can help analyze different mechanical properties of materials or components. Output values are, e.g. the Young’s Modulus, yield point, flexural modulus, ultimate tensile strength, strength of an adhesive bond and many more, depending on the material or part. They are therefore used to answer questions like, e.g., “How strong and stiff is my sample?”, “How much can my sample elongate or stretch?” or “How much can my sample compress or flex before breaking?” The important data derived from the answers is used by engineers in R&D and QC. Although UTMs are commonly used for testing of large-scale, robust components, they are not limited to high force/high torque applications. While classical UTMs can achieve forces up to 5000 kN depending on the model, small-scale, soft or fragile parts can also be characterized, as long as the forces and deflections involved can be accurately measured by the transducer.

Important terms and variables: (more possible)

Term	Symbol
Young’s Modulus	E
Shear Modulus	G
Poisson’s ratio	ν
Extensional viscosity	ηE
Flexural Modulus	EFlex
Bulk (Compression) Modulus	K
Engineering strain
Engineering stress
Normal force	FN
Torque	M
Displacement	s
Deflection angle	φ

A sample of the material or a component is placed in the UTM and held by grips or special fixtures. The sample is then subjected to a force or torque (stress), and the resulting deformation or deflection (strain) is measured or vice versa. As the dimensions of the sample are known, stress-strain curves can be generated from the recorded forces and deformation, which in turn allows prediction of the materials’ or components’ behavior in operating conditions.

UTMs are commonly used for high-force/high-torque applications. Conventional UTMs do not provide suitable fixtures, torque/force presets are not precise enough, and sensors lack the necessary sensitivity to deliver useful data from the measurement of very small-scale parts and components. There is an increasing need to test smaller and softer devices and materials, but for most of these applications no commercial instruments exist and researchers therefore need to rely on self-made solutions in order to characterize their components.

Combining traditional mechanical testing methods with a rheometer set-up takes advantage of the high accuracy of the optical encoder and the excellent torque resolution of its EC drive to allow measurement of even the smallest torques and deflections. Due to its lift drive and the possibility of usage of an additional lower linear drive, it is also able to measure small normal loads and displacements. In combination, this enables characterization of parts and components previously not accessible to characterization. Furthermore, additional environmental parameters such as temperature or relative humidity can be set, allowing characterization of very small parts under a wide range of environmental conditions that can be experienced during operation.

Test Setup:

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(Source: W. Eom et al. – Carbon nanotube-reduced graphene oxide fiber with high torsional strength from rheological hierarchy controlDOI: doi.org/10.1038/s41467-020-20518-0)

Test Setup:

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Results:

Test Setup:

Results:

A very wide range of materials and components can be tested with a UTM. Various fixtures and grips are needed to securely clamp the components during testing, and to prevent measurement errors. The choice of fixture depends on the test methods.