Design Guide - Solvay Plastics

Table 18: Poisson’s Ratio for Amodel Products
Grade
Poisson’s Ratio, υ
ET-1000 HS 0.40
A-1115 HS 0.41
AS-1133 HS 0.41
AS-1145 HS 0.41
A-1230 L 0.31
A-1240 L 0.29
A-1340 HS 0.38
Long-term Mechanical Properties
In order for any engineered component fabricated from
a polymeric resin to perform within specified parameters
throughout its intended design life, the design engineer
must consider the long term effects of a number of
factors. A variety of stress loads as well as property
changes due to environmental factors must be taken
into consideration. To assess the time related effects
of stress on the behavior of polymeric materials, creep
and fatigue properties are measured. A wide variety of
environmental factors can also affect the performance
of an engineered component and this subject is
discussed in detail in the section entitled "Environmental
Resistance" starting on page 58. However, certain
environmental factors are so pervasive that it was
deemed appropriate to consider them in this section.
These are the effects of moisture absorption and longterm
exposure to high ambient temperatures.
This section will present data generated to assist the
design engineer with the analysis of design life
requirements. The data in this section includes:
• Creep modulus in tension, flexure,
and compression modes
• Tensile creep rupture
• Fatigue endurance
• Property changes due to moisture absorption
• Dimensional changes due to moisture absorption
• Property changes due to long-term exposure to
elevated temperatures
The long term property data presented in this manual
has been generated to show trends and property loss
for a number of Amodel ® PPA grades under a variety of
representative conditions. Due to the time required to
generate the data, not all grades or sets of conditions
can be included. The data are intended to show trends
as a function of filler/reinforcement systems so that the
designer may make educated decisions.
In some instances, attempts to generate data on long
term properties utilize “accelerated” test conditions
to speed data acquisition. Caution should be taken
when evaluating data generated in this manner as it is
often non-linear. This is especially true when measuring
property loss as a function of elevated temperature
and/or chemical exposure. Thermal "thresholds" such
as the glass transition temperature (T g ) and ultimately,
the melting point are the main contributors to this
non-linear behavior.
Creep
When a material is subjected to stress, an immediate
strain occurs. For small strains, this strain is proportional
to the stress and calculable from the appropriate
modulus. If the application of stress continues for
an extended period of time, additional strain may be
observed. This behavior is referred to as creep and the
additional strain as creep strain.
While creep is observed in metals, the phenomenon
is more significant with plastics. Their lower modulus
means that at the same stress level, the magnitude of
the strain is larger and a higher proportion of ultimate
strain. In general, the closer the initial strain is to
the ultimate strain, the more likely it is that creep is
significant.
The reality of creep must be factored into a design to
ensure long term satisfactory performance. The initial
task is to determine if the creep will have a significant
effect on the dimensions or function of the part. If the
stress levels are low enough so that any dimensional
change will be insignificant, creep may be ignored.
However, if the stress levels are such that creep will
result in unacceptable deformation, an alternative design
must be considered. This may include investigating a
material with a higher creep modulus, or incorporation
of an alternate design such as a metallic insert to serve
as the load bearing member. Additional discussion can
be found in the Design section.
Property Data
Amodel ® PPA Design Guide
31