Hard Spots

Discontinuities that will cause stress risers & premature failures
Hard Spots, smard schplots, you say........ as I was just trimming my shrubbery, a perfect example came to me: I was breaking dead branches so they would fit into my trash bin. Little ones, I could easily break between my hands. As they got bigger, I broke them over my knee. Perfect example of a hard spot!!

Trying to break the stouter ones between my hands caused the sticks to bend, but not break. The moment I introduced the hard spot (my knee), I could break them easily, because my knee caused a stress riser.
Rail crack under the forward heel of a sandwich kite board
Marinetex field repair ground off

Water begins to ooze out
Outer fiberglass ground away.

Fracture visible in Carbon cloth that emerges from beneath edge of veneer heel reinforcement
Carbon cloth ground away.

Fracture visible in PVC sheet foam
Fractured PVC sheet foam ground away some more.

Fractures radiate from edge of veneer reinforcement.

This edge acted as a hinge, with the very rigid veneer patch digging into the much more flexible PVC-based structure beneath it.

Placing such an edge near a major load (heel) is a sure-fire way to cause premature failure.

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