The Meaning of ''Extensional'' In This Phrase

[majidfirouzeh]

What does ''extensional'' mean exactly in this essay?
what is ''lower- and upper-bound solutions''?

Extensional collapse modes of structural members


Abstract-In recent years considerable crash-dynamics research has been devoted to improving passenger
survivability in transportation vehicles of all types. One of the objectives of this research is to attenuate the load
transmitted to an occupant by the structure, either by modifying structural assembly, changing geometry of its
elements, or adding specific load-limiting devices to help dissipate kinetic energy.
General aviation aircraft (both rotary and fixed wing) have fuselage subfloors of a built-up structure which are
generally very stiff perpendicular to the floor of the cabin. The subfloor structure, designed to crush at an
appropriate force level, can be used to advantage in a crash by dissipating energy through plastic buckling of the
floor beams and frames. Simple closed-form solutions to predict the mean crushing-force levels of subfloor designs
would be useful in engineering practice. With that objective in mind, the complicated problem of analyzing the
crushing process of thin-walled, plate-formed, open structures with particular emphasis on “L” and cruciform
shapes has been successfully attacked by using a simple type of analysis.
Lower- and upper-bound solutions for the mean crushing strength of cruciforms have been obtained by
considering modes of deformation which account for both bending and extensional deformation. The analysis and
experimental data show the importance of extensional deformation to the energy absorption process, representing
at least one-third of the dissipated energy.

 

[JStephen]

Just reading your quote there- I would say extensional means along the axis of the member, so axial tension or compression.
"Upper and lower bound solutions"- I would take to mean approximate solutions, one of which is probably greater than the actual strength, one of which is probably less than the actual strength, with actual strength at some unknown point in between.
That's not my field, just reading the text here.

 

[Jboggs]

I agree.

 

[RolMec]

Extensional deformation is solely related to tensional states, in delimitation to compressional deformation. This would however on first sight contradict some parts of the abstract, specifically the implications of "crushing" processes.
Perhaps the finding of the essay is, that due to tensional deformation (e. g. as part of bending), a substantial energy dissipation is achieved. If that is correct, the essay should give exactly this input about the appearances and conditions of tensional deformation in crushing processes etc.
Or perhaps the expression / wording was not chosen sufficiently precise, refer e. g. "attacked".
Lower- and upper - bound(ary) solutions might relate to the following expression of mean (or average) crushing strength, solution in the meaning of the numeric value of the strength limits.
Is this essay perhaps a translation into English?

P.S.: The essay itself was not to be downloaded, e404.