Biomedical Engineering Reference
In-Depth Information
is an important characteristic of wear performance, can also be assessed
(trans-vinylene index).
Differential scan-
ning calorimetry
Differential scanning calorimetry is a technique to measure how much
heat flow is required to increase the temperature of a substance. This is
particularly useful in measuring properties of phase transitions (tran-
sitions between solid, liquid, and gaseous states) or glass transitions
(liquid-glass transition from a hard and relatively brittle state into a mol-
ten or rubber-like state) in a substance. This technique has wide appli-
cability in determining the purity of manufactured substances, checking
the composition of polymers, and analyzing curing processes for poly-
mers and drug compounds. This can be useful in evaluating the effects
of processing and manufacturing of the devices.
White light inter-
ferometry
White light interferometry can be used to measure the three-dimen-
sional microstructure and topography of a specimen surface, otherwise
known as the “roughness” of a surface. The method analyzes the inter-
ference pattern of a wave directed at a location of interest and a reference
wave. Depending on the path traveled by each wave, they later combine
and result in some degree of constructive or destructive interference,
which is captured by a detector and processed to characterize the surface
roughness. White light interferometry is often used to examine the sur-
face roughness of components that articulate or rub against one another
and can aid in determining wear mechanisms.
Gel permeation
chromatography
Gel permeation chromatography (GPC) is a method for measuring the
proportions of the constituents of a material, using the relative perme-
ability of the constituents. The technique is carried out by pouring a
solution of the sample (dissolved into a solvent) into a column with gel
layers that are designed for a range of molecular weight. Depending on
permeability, the gel will retain some constituents and will not retain
others. Various detectors can then be used to analyze the separated sam-
ple. GPC can be used to determine a polymer's molecular weight distri-
bution or to determine changes following degradation.
Tools for design: material modeling
Material modeling in the form of computer simulations can also be used
to evaluate how a material will respond to certain loading conditions.
Historically, computer simulation or finite element analysis (FEA) is
used to solve complex structural problems in traditional fields such as
civil and mechanical engineering. The foundation of the FEA approach
is based on numerical modeling of physical systems using small inter-
connected building blocks (finite elements) that resemble the geometry
of the structure. By breaking a single complex problem into numerous
simple problems, the deformation, strain, and stress can be mapped
throughout the entire structure (Figure 15.3). The utility of any FEA
results depends on the validity of the model inputs. Key components of
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