Structural Engineering & Statics
where the load goes
Generator

The crack-strength generator

Rendered here at the parameters it defaults to, with every essay that calls it — which is the same list as the blast radius of changing it.
The crack length at which the strength stops matteringFailure stress against crack length for a toughness of 100 MPa√m, with one steel grade drawn. The falling curve is fracture — Kc divided by Y times the root of pi a — and it does not know what the yield stress is. The horizontal lines are the grades. At 355 N/mm² the two cross at a crack 20.1 mm long. Below that the section yields and the crack is irrelevant; above it the crack decides and the 355 is irrelevant.501001502000100200300400500crack length, mmstress at failure, N/mm²355 N/mm² crosses at 20.1 mmfracture: the crack decides

2 essays call crack-strength. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.

Where it is called

Changing this generator changes every one of these figures.

501001502000100200300400500600crack length, mmstress at failure, N/mm²275 N/mm² crosses at 33.5 mm460 N/mm² crosses at 12.0 mmfracture: the crack decides Materials

The flaw that sets the strength

A member with a crack twenty millimetres long fails at its yield stress. Make the steel stronger and the crack that does it gets shorter, so the same flaw that was harmless in the weaker grade decides the stronger one.

 10⁴10⁵10⁶10⁷10⁸2050100200500cycles to failurestress range, N/mm²category 160category 90category 366.8e+74.3e+62.7e+5working range 70 N/mm² — the lives are marked Materials

The load that never came near failing anything

A detail survives sixty-eight million cycles at a stress range that another detail in the same steel survives two hundred and seventy thousand of. The two lie a factor of two hundred and fifty apart, and the material is not on the plot anywhere.

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