This
is a versatile test and can be applied to many types of products that
are available in, or can be cut or shaped into, elongated test beams.
The
most conventional method is a three-point bend test in which the
specimen is supported horizontally at either end like a bridge and a
probe moving downwards bends it in the centre. As the specimen bends it
stores up strain energy, which is dissipated in cracking at the point of
fracture.
Compression tests can be carried out on a wide variety of products that experience such a force in natural conditions.
These
may include fruit and vegetables, puffed cereals, cakes and biscuits,
confectionery and pharmaceuticals.
Normally, as these products may be oddly
shaped, a compressive test is the most reliable way of assessing their
fracture behaviour.
Many
foods and pharmaceuticals are not normally subject to tensile forces in
their manufacture and consumption. There are, however, exceptions, e.g.
dough, gels, spaghetti and adhesives.
These
tests can also be performed on materials from which elongated test
specimens can be cut and gripped within the clamps of the Texture
Analyser to be stretched. This could include fruit, vegetables and meat.
In any case this type of test yields reliable results for tensile
modulus, yield stress and strain, strength and strain to fracture, and,
if the crack area can be measured, the fracture toughness of the
material.
Fracture
is simply crack propagation. Force has to be exerted to initiate a
crack, then energy has to be supplied to propagate it. This is the
energy that goes into breaking the bonds within the material in order to
generate new surfaces.
There
are three ways a crack can propagate within a material. All structural
failures are the result of material failure in one of these three modes.
What
is Fracture? This is the first of a set of blog posts on the subject of
fracture testing. Traditional information on fracture testing focusses
on techniques for assessing engineering materials using standard methods
and strict geometries. However, these may not be so useful for the
typical user of a Texture Analyser.
The loosest definition of fracture is “a form of failure in which the material separates into two or more pieces due to an applied load”.
Fracture strength is the stress at which a specimen fails or fractures.
Fracture can be brittle, ductile or semi-ductile. This refers to the
nature of deformation and will be covered in the next post.
More
than ever before, the food industry is finding itself forced, through
outside pressures, to improve constantly its product quality and to
maintain that quality at a consistently high level. Food quality is an
important concept, because the foods people choose depend largely on
quality.
Consumer
preference is important to the food manufacturer, who wants to gain as
wide a share of the market for the product as possible. Quality is
difficult to define precisely, but it refers to the degree of excellence
of a food and includes all the characteristics of a food that are
significant, and that make the food acceptable.
Back in February, Kendra Pierre-Louis of Popular Science wrote this interesting article.
She indicated that ‘Tweaking texture could give us healthy versions of our favourite junk foods—and that's just the beginning.’
She
talks about how she has embraced culinary novelties such as glass
potato chips, grilled whale and poisonous shark but cannot stomach the
sensation of hollandaise sauce.
Apart
from crispy foods like crackling, British consumers embrace
softer-feeling food. Industrialised, processed food is often marketed
as soft and creamy in the UK, with adverts for such foods playing on the
sensual and comfort associations that have set in from a young age.
Our childhood association with pureed food is one of the reasons we turn to soups when we are ill.
This
is a versatile test and can be applied to many types of products that
are available in, or can be cut or shaped into, elongated test beams. 
Compression tests can be carried out on a wide variety of products that experience such a force in natural conditions. 
Many
foods and pharmaceuticals are not normally subject to tensile forces in
their manufacture and consumption. There are, however, exceptions, e.g.
dough, gels, spaghetti and adhesives. 
Fracture
is simply crack propagation. Force has to be exerted to initiate a
crack, then energy has to be supplied to propagate it. This is the
energy that goes into breaking the bonds within the material in order to
generate new surfaces. 
What
is Fracture? This is the first of a set of blog posts on the subject of
fracture testing. Traditional information on fracture testing focusses
on techniques for assessing engineering materials using standard methods
and strict geometries. However, these may not be so useful for the
typical user of a Texture Analyser.
Back in February, Kendra Pierre-Louis of Popular Science wrote this interesting article. 
