Texture Analysis Professionals Blog

How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 16 October 2018

The Measurement of Hysteresis using a Texture Analyser

Testing mattressHysteresis in the context of deforming a material is the loss of energy in the form of heat when a sample is loaded then unloaded. 

This occurs due to internal friction, and so the effect is larger for a material such as rubber, which requires the movement of large molecular chains each time it is stretched or compressed. If a piece of rubber is deformed several times in the hands, this loss of energy can be felt directly as the sample heats up. 

As can be seen on the graph, the deformation of a viscoelastic material follows a different path on the load and unload cycles. The unload cycle shows that the material is slower to recover compared to the load cycle. This difference in recovery is known as hysteresis, which is due to energy dissipation by the generation of heat.

Tuesday, 9 October 2018

Compression Testing using a Texture Analyser – Calculating Fundamental Parameters

Squeezing sponges
Compression testing involves a self-supporting sample being compressed under a flat probe large enough to cover the whole sample. 

The loading arm (attached to the probe) moves down at a constant speed to deform the sample, first deforming it elastically then plastically (if it is not completely brittle). If the force required to break the sample is within the limit of the load cell, fracture may occur. However, this is not always the case in compression as many samples are stronger (or tougher) in compression than in tension, especially ceramic samples.

Tuesday, 2 October 2018

Three Point Bend Testing using a Texture Analyser – Calculating Fundamental Parameters

TA.HD plus 3 point bend test on plastic sample
When a customer is presented with an elongated or flat food sample, one of the first things they might do is snap it between their hands. 

During this process, they are subconsciously assessing whether the food product is brittle or ductile, stiff or compliant, and strong or weak. Consequently, bend testing is a technique used very frequently by Texture Analyser users, covering everything from the snap of tablets to the toughness of dog chews. 

The analysis of this type of testing is often limited to looking at a force peak and maybe the distance to fracture. It is a very useful test for monitoring quality of irregular objects. However, this test setup can also provide useful stress-strain data if the sample has a uniform cross-section, providing accurate measurements are made of the sample dimensions. “Flexure” and “bending” have the same meaning and are often used interchangeably.

Tuesday, 25 September 2018

Tensile Testing using a Texture Analyser – Calculating True Stress and True Strain

Texture Analyser film tensile testThe calculation of parameters from the stress-strain graph of a tensile test has already been covered in a previous blog post. 

The calculations considered were those most often used when referring to stress and strain, and to give them their full name they would be called “engineering stress” and “engineering strain”. It is usually safe to assume that every time stress and strain are mentioned in the literature, this refers to the engineering values.
 

However, as the load on a sample increases, the cross-section over which the force is applied changes (it gets thinner). If the engineering stress is used (taking into account the initial area), the stress is underestimated. True stress solves this issue by using the instantaneous area over the course of application of load so that as the cross-section changes, the value of stress is calculated using the new cross-sectional area.
Additionally, whereas engineering strain is the amount that a material deforms per unit length, true strain is the natural log of the current length over the original length.

Tuesday, 11 September 2018

Tensile Testing using a Texture Analyser – Calculating Fundamental Parameters

TA.HDplus tensile testing
Tensile testing involves a sample held in two grips a set distance apart. The loading arm (attached to the top grip) moves up at a constant speed to deform the sample, first deforming it elastically then plastically. If the force required to break the sample is within the limit of the load cell, fracture will occur.

It is a very useful test for monitoring quality of irregular objects, such as the toughness of pizza or the texture of fish. However, this test setup can also provide useful stress-strain data if the sample has a uniform cross-section, providing accurate measurements are made of the sample’s dimensions. “Dogbone” shaped specimens are often used in tension, with two wide sections tapering to a narrower central section.

Indentation Testing using a Texture Analyser – Calculating Fundamental Parameters

Although it has long been known that some materials are harder than others, indentation tests to find quantitative hardness values only came about in the 1800s. 

Once it was established as a valuable technique, hardness testing machines started to appear on the market early in the following century. Old fashioned indentation testing involved the application of a weighted probe onto a flat sample surface that was left for a set time period. The hardness of the sample was calculated from the area of the residual dent left in the sample. “Instrumented” (computer controlled) indentation testing has now been in use for many years, and involves the collection of force, displacement and time data, which is why the Texture Analyser is so well-suited to this type of measurement.

Tuesday, 4 September 2018

Plasticity Measurement of Soft Solid Foods

Spreading butter on crumpetPlasticity is a property shown by many materials, such as polymers, metals and the majority of foods. It is the ability of a material to undergo permanent deformation. 

If you press your finger on a spring, it returns to its original shape. If you made that spring out of cheese, it would not spring back as far – it would remain squashed. When stretching a sample, plasticity is seen on the force-distance graph as a change in gradient after the initial linear section (straight line). The point where the gradient changes is known as the ‘yield force’. If this point is reached and more force is applied, the sample will be permanently changed. Before this point, the behaviour is elastic and spring-like.

Tuesday, 28 August 2018

Food Texture: A video, a webinar, latest research and capturing more

Eating a cheesy pizza
Explaining texture preference
 
Understanding texture preference and the trends that may result in consumer behaviour change is an area of great opportunity. However, remaining agile before a consumer shift occurs can be a challenge.

A new webinar will address this challenge and will offer:

• A view on techniques to forecast upcoming influences on food trends 


• A perspective on the linkage of newly monitored issues to texture and the process used to deliver higher value commercial insights 


• Expertise on driving rapid product development through localising relevant texture trends from around the world

Speakers: Janet Carver, Culinology Group; Mary Lynne Shafer, Ingredion; Susan Badarroco, Culinary Tides.


Watch this webinar to learn more...