In laboratories around the world, scientists are finding new ways to manipulate matter at increasingly small scales, as well as drawing inspiration from biological materials.
This revolution is giving us substances with properties that were once confined to the pages of science fiction books. But these materials are more than just scientific curiosities – they are genuinely useful, to the point that as applications start to emerge they will radically change our world.
As any material scientist knows, physical characterisation is key to understanding the properties of these new and existing materials, how their properties are affected by changing formulation, manufacture etc.
Not just for texture analysis...
If you’re looking for a pair of trainers woven from stainless steel, a plastic coated fabric that changes colour with temperature or a transparent material that stops bullets in their tracks, you will need to, at some point, test these materials to quantify such properties as compressional strength, flexibility, tensile strength, puncture resistance, etc.
This is where a Texture Analyser/Materials Tester can be employed to compress, bend, stretch, extrude, cut, puncture or snap a product and provide an objective analysis of the material’s physical capabilities.
Here are just a few applications of measurement that will come in useful for the assessment and characterisation of new and existing materials.
Break away from Standard Material Characterisation
Our world is changing and the above examples are a small illustration of the wide range of industries in which Texture Analysis/Materials Testing is becoming an indispensable aid to research and development.
To date, the Materials Testing world has been bound by testing using Standard Methods. As many will have experienced, the chosen Standard Method might not fully measure the range of physical properties of the sample. Additionally, the Method may restrict the sample preparation or dictate a sample form that is not easy to prepare or typical of the newly designed material. Indeed, a Standard Method might not even exist for the newly created material or material form.
And that is where Stable Micro Systems provide their ‘out of the box’ applications thinking to apply the most suitable test configuration and settings for characterisation of your product. We do not restrict the best sample method to Standard Methods; rather, we provide bespoke test sequences and rigs that best suit the properties you are trying to measure. Why be constrained when you can optimise your product testing?
If you still prefer to take a fundamental testing approach…
Texture Analysers are very often used for quality control of irregular products by the use of empirical measurements.
The force required to crush a tablet or the distance a biscuit bends before it snaps are invaluable pieces of information to manufacturers looking to develop new products or ensuring products perform correctly during spot checks. This type of test is ideal for products that have an unusual geometry, but it is also useful for testing more complicated systems, such as the combination of a product and its packaging (a box of eggs, the force to open a ring pull can or a yoghurt in its pot), with the added benefit of time saved by allowing a product to be tested straight off the supply line.
However, a large number of users use the suite of Texture Analysers to calculate more fundamental parameters by taking into account the geometry and dimensions of the sample, as well as the specifics of the test set up along with the relevant engineering equations.
The following example rigs allow the fundamental approach to testing:
Over the years, Stable Micro Systems has incorporated a large number of test procedures and analysis methods suitable to obtain fundamental materials parameters that could be used across a wide range of industries. Whilst the equipment can provide a simple and flexible empirical solution, it is also able to offer the traditional measurements well established within the materials industry.
Data Analysis and Engineering Calculations
Standard engineering calculations are built into Exponent software for quick calculation of specific moduli, stresses, strains, strengths and energies which are particularly suited to materials testing applications. Each calculation is designed to be used with a very specific test setup (for example, cuboid three point bend testing) as the specific equations required for analysis depend on the sample and test geometry.
A help page is supplied for each quick calculation, explaining the parameters that must be entered into the software by the user (such as film thickness) and a derivation and reasoning behind every equation used. The quick calculation macros should be studied before they are used so the user is familiar with how each macro works, and edit the macro if further calculations need to be added, or existing calculations tailored to the specific behaviour of the test sample.
Types of test and their analysis possibilities:
Regardless of whether the test is performed in compression or tension, a resulting curve can be analysed to obtain the following typical parameters:
• Strain rate
• Young’s Modulus
• Tangent, chord and secant modulus
• Yield stress
• Strain to yield
• x% proof stress
• Maximum stress
• Strain at maximum stress
• Energy to maximum stress
• Breaking strain
• Hysteresis %
• Energy to failure
When specifically measuring in tension, additional parameters may include:
• Necking onset
• Ultimate tensile strength
• Strain hardening parameter
• Strength coefficient
Flexure using three point bend for cuboid and cylindrical samples:
• Yield stress
• Young’s Modulus
• Flexural strength
Indentation using conical and spherical probes:
• Indentation modulus
• Elastic energy
• Plastic energy
• Indentation energy
Puncture of uniform thickness thin films using spherical probes:
• Failure Strain
Why change from the Standard Method approach?
A Standard Test Method is a definitive procedure that produces a test result. In order to ensure accurate and relevant test results, a Standard Test Method is explicit, unambiguous, and experimentally feasible, as well as effective and reproducible. A Standard Test Method can be considered an experiment that determines one or more characteristics of a given sample and the detail of the test method is usually as a result of creation from a number of experts in that measurement field. Within the materials testing industry, for example, there are an enormous number of Standard Methods (e.g. ASTM, ISO) that have been developed to measure specific sample characteristics. Typical examples of those that use Texture Analysers or Materials Testing equipment are:
• ASTM D882-02: Tensile test of thin plastic sheeting (thickness under 1mm)
• EN 1944:1996 – Self Adhesive Tapes – Measurement of Unwind Adhesion at Low Speed
When reporting results in an academic paper or industrial report, these Standard Methods will have been adhered to for the collection of the results and are more globally understood by others using the same Standard Methods. It is for this reason that Standard Methods have their place in the laboratory.
In the food industry, for example, there are far fewer Standard Methods for physical property measurement. However, you may already be following one of few specific Standard Methods to test your samples, e.g. ISO Gelatine Bloom Strength, AACC Bread Freshness, AACC Pasta Firmness, ASTM Petroleum Wax Firmness, ASTM Adhesive Peel Strength.
The limitations of applying standards, however, is that their biggest advantage (of being specific) can be a major disadvantage (or restriction) to the measurement. All too often, operators are forced to use a Standard Method to measure a property of their product when:
• The property that the Standard Method measures is not the most important, or interesting, measurement that could be performed on the sample, or
• The sample preparation procedure may be difficult (or impossible) to conform with given the sample to be tested is different to the sample for which the test method was developed.
A well-written test method is important. However, even more important is choosing a method of measuring the correct property or characteristic. Not all tests and measurements are equally useful; usually a test result is used to predict or imply suitability for a certain purpose. However, it would seem more important to measure the most important characteristics of a product than to follow a seemingly pointless Standard Method that does not ideally characterise the product.
If you’re not bound by any existing constraints and are looking for the most simple testing solution, sometimes the easiest approach is to set up a test that closely imitates the way the product is evaluated in real life. This is called an ‘Imitative Test’. This type of test usually also makes data interpretation easier for you to understand.
For certain industries, consensus regarding the method of measuring the physical characteristics of products is virtually impossible and whilst procedures can be agreed upon internationally, they are not always universally accepted. Standardisation of methods is essential if investigations carried out by different groups are to be directly comparable.
The methods used for physical testing should measure the desired characteristics necessary to monitor the process, but need not always be comparable with other laboratories, where different criteria may be important. Where international comparison is important, it is essential that methodologies be standardised. This would include all aspects of the testing procedure and this is an area of which the reference methods are primarily directed.
In contrast, where direct measurements are being made of the physical properties of a product, the experimental methodologies should not be constrained by reference methods. Instead, researchers are encouraged to develop and use methodologies that enhance the precision and accuracy of testing methods and lead to an understanding of the basic mechanisms. It is likely that new understanding will lead eventually to methods that more closely predict consumer assessment of product characteristics.
The Stable Micro Systems range of Texture Analysers provide the flexibility of testing principles (e.g. compression, penetration, tension, extrusion, etc.) and the endless option of probes, fixtures and data analysis techniques within the software for texture analysis and fully customisable test settings.
Whilst Standard Methods are particularly useful for traditional material forms that have not changed over the decades and are fully accepted, there lies another world where creativity has taken off into new materials and material forms for which these Standard Methods cannot be applied. One example of such an issue is in the field of pharmaceutical development. Traditional methods are well established for the testing of tablets, gels, suppositories, medicated liquids that are manufactured in their traditional form; however, innovative dosage forms have been developed such as disintegrating films, capsules, chewable pastilles for which there is no Standard Method to apply for the measurement of their physical (or textural) characteristics. Alternative testing methods that accommodate the testing of samples of varying types and dimensions and the range of additional material characteristics which can be measured, are required.
Not only are new non-standard methods viable where sample dimensions cannot be prepared according to the standard, but also where the operator may wish to modify the test parameters (such as the test speed) to more closely mimic the situation under which the sample is to be typically used.