Stress is the intensity of a force that structural
material must bear. It is expressed in pounds
of force per square inch. Stress can act in different
directions: pulling apart (tensile);
pushing together (compressive);
and shear (forces that slide
adjacent regions past one another, like a deck
Bag failure begins at places where (a) the stress
is constant and exceeds the level that the material
can sustain (b) or in places where the bag is
weaker (e.g., place where an attached handle is
welded or glued) failure is likely there.
What else can cause stress to be higher in some places more than
others? To understand this, you need to look for concentration of forces and at
how the bag's structure transmits its load forces to the handles.
But when the force might be carried anywhere
within the whole width of the side of the bag,
how do you decide where failure is likely to occur?