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Structural stress vs total stress 1
- Thread starter Pawel27
- Start date
SWComposites
Aerospace
Have never heard of "Structural stress". In what context is this used?
Sometimes there is "mechanical stress" due to applied forces and "thermal stress" due to temperature changes, with the combination referred to as "total stress"
Sometimes there is "mechanical stress" due to applied forces and "thermal stress" due to temperature changes, with the combination referred to as "total stress"
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1
- Thread starter
- #3
Below extract from Zeman book "Pressure vessel design: the direct route, Tom 10":
In some design checks, structural stress or strain have to be determined. Some models may give these directly, e.g. some finite element models using shell or beam elements. In cases where the model does not give structural stress and strains directly, e.g. because local structural perturbation sources are kept in the model or are introduced by geometrical idealization, the required value of the structural stress or strain in a critical point (hot spot) may be:
- determined by...
- replaced by the total stress or strain in any model that deviates from the stress-concentration-free model only in local structural perturbation sources. Of course, total stress or strain in the model investigated may always be used instead of the extrapolated values, with the total stress or strain being determined by the software's solution..."
In some design checks, structural stress or strain have to be determined. Some models may give these directly, e.g. some finite element models using shell or beam elements. In cases where the model does not give structural stress and strains directly, e.g. because local structural perturbation sources are kept in the model or are introduced by geometrical idealization, the required value of the structural stress or strain in a critical point (hot spot) may be:
- determined by...
- replaced by the total stress or strain in any model that deviates from the stress-concentration-free model only in local structural perturbation sources. Of course, total stress or strain in the model investigated may always be used instead of the extrapolated values, with the total stress or strain being determined by the software's solution..."
I believe the reference is alluding to the potential error between the assumptions made in applying loads when modeling and the actual loads in service. While we attempt to converge those, they are sometimes different.
As an example, if we apply loads to a beam, a tank or other structure using a particular loading scheme (say point loads), our stress result is rather broad and applies to the whole section without regard to the actual point of load application and the concentration of stress at that particular point. If you do an FEA of the same condition and return the von Mises stress distribution for the area around the point load application, your analytical result will be different and might be critically different; yet we usually only check the gross condition.
As an example, if we apply loads to a beam, a tank or other structure using a particular loading scheme (say point loads), our stress result is rather broad and applies to the whole section without regard to the actual point of load application and the concentration of stress at that particular point. If you do an FEA of the same condition and return the von Mises stress distribution for the area around the point load application, your analytical result will be different and might be critically different; yet we usually only check the gross condition.
- Thread starter
- #5
I have found answer to my question in EN 13445-3:2009:
"B.2.17
structural strain
strain in a stress-concentration-free model of the structure, i. e. the strain determined in an idealised model which
takes into account the real geometry of the structure with the exception of the local details which cause only local
stress/strain concentrations, see B.7.6
NOTE 1 Structural strain includes the effects of gross structural details (e. g. branch connections, cone-cylinder
intersections, vessel-end junctions, thickness discontinuities, presence of attachments, deviations from design shape with global
effect, such as out-of-roundness of cylindrical shells). However it excludes the notch effects of local structural details, such as
small fillet radii, weld toe details, weld profile irregularities, small (partial penetration) bores, or of local temperature field details.
NOTE 2 Finite element shell or beam elements may give structural strain directly.
B.2.19
total stress / strain
total stress/strain in a design model which includes all stress/strain concentration effects, non-local and local"
"B.2.17
structural strain
strain in a stress-concentration-free model of the structure, i. e. the strain determined in an idealised model which
takes into account the real geometry of the structure with the exception of the local details which cause only local
stress/strain concentrations, see B.7.6
NOTE 1 Structural strain includes the effects of gross structural details (e. g. branch connections, cone-cylinder
intersections, vessel-end junctions, thickness discontinuities, presence of attachments, deviations from design shape with global
effect, such as out-of-roundness of cylindrical shells). However it excludes the notch effects of local structural details, such as
small fillet radii, weld toe details, weld profile irregularities, small (partial penetration) bores, or of local temperature field details.
NOTE 2 Finite element shell or beam elements may give structural strain directly.
B.2.19
total stress / strain
total stress/strain in a design model which includes all stress/strain concentration effects, non-local and local"
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