Add some facility or output result for detecting material failure

[stfnp]

In GitLab by spfeifer on Aug 25, 2017, 20:21

Alternative 1: Add material strength as an optional input parameter. If present, draw a line on the stress graph and mark points of failure.

Alternative 2: Add material utilization (stress divided by material strength) as an output and mark points of failure. Material utilization of different layers can later be combined easily (maximum).

Alternative 2: Use an energy criterion to judge material utilization, e.g. resilience

Problem with all of that: Materials like wood where compressive strength =/= tensile strength

[stfnp]

In GitLab by ozra on Jan 8, 2018, 03:38

I really like the idea of this.

Why not allow entering both tensile, compressive and shear-strength (take my terms with the grain of don't-know-physics-much salt)?

[lleroy]

(from issue gitlag-122)

it would be nice to also be able to specify the rupture and compression breakdown stress for a layer,
and to have a line on the graph to see whether the stress in a layer is too high.

[stfnp]

This might be worth reading:

• An Introduction to Sandwich Structures - Dan Zenkert
  • Chapter 2: Materials and Material Properties
  • Chapter 7: Failure Modes and Design Criteria

[Puujousi]

In my opinion the best option is to use strain as a definitive parameter. Stress as such is not so important, but strain is. Especially with wooden bows the maximum strain (in tension) wood can tolerate is about 0,7–1,0 %. In compression the elastic limit is about 0,5 % strain. This is essential, because the strength of the wood can vary a lot. For example, Modulus of rupture can be as low as 30 000 kPa (Cottonwood) and up to 200 000 kPa for tropical hardwoods (Kaneelhart). So, the stress as such is not telling how close the bow is breaking. But the maximum strain value is quite near constant regardless of wood species.