Let’s take the femur as an example. How much force would it take to snap it in half; I’m pretty sure I couldn’t break one over my leg. What about crushing one? Yeah it would hurt if an elephant stepped on your femur, but would it compress it enough to leave a mark, or turn it to dust? Also, how much tension and torque could a bone take before breaking it?
No, I am not morbid; just curious.
The Mythbusters worked on this problem, when they replaced their crash test dummy Buster with a Mk II model crafted by Jamie. I seem to recall that 3/4" ash had breaking strength comparable to a femur bone in Jamie’s test rig. You should be able to quickly Google for the exact snapping force, but that’s a good visual comparison from the episode.
If I remember, it was 600-700 lbs.
If movies have taught me anything, it is that they are about as strong as a pretzel stick.
anyone old enough to remember that educational film showing an aldult femur held upright and supporting a volkswagen beetle lowered slowly on to it?
Lest anybody acquire odd ideas, I’ll note that joints will give way under far less shock or pressure. Also bones vary in strength: the clavicle is more fragile than the femur.
This webpage lists some mechanical properties of human femurs and mandibles based on age (bone becomes weaker with age).
For a 20-30 year old, the ultimate tensile strength (that is, the point where the bone breaks under longitudinal tension) is 123 MPa, in compression it’s 167 MPa, bending and torsional are 173 MPa and 57 MPa respectively.
The following is a WAG:
Bone is a brittle material, so it does tend to fracture and shatter. Based on the skiing accident of a friend of mine, in which his tibia and fibula were broken in bending, the compression side of the breaks were shattered into many small shards (most of which had to be removed; it took 2 years to close the gap with regrowth). Based on that alone, I’d guess that an elephant would crush a human femur into little shards, but not dust.
Out of boredom, using lots of assumptions
Mass of an Asian Elephant = 5000kg
Weight = 5000*9.8 = 49000N
Case1:
Assume distributed evenly on each foot = 12250 N force applied by an elephant’s leg
Dimensions of human femur (average, male) = 0.48m x0.03 m = 0.0144m^2
Assume entire applied force from elephant leg is distributed evenly onto the femur = 12250N/0.0144m^2 = 0.85 MPa compressive load
Case 2:
Assume entire mass of elephant transferred (they apparently have a gait that allows for only one foot on the ground):
49000N/0.0144 = 3.4 MPa
I expected higher in both cases.
Disclaimer: I was bored enough to do this, but tired and lazy enough to not check my math or really even my assumptions. I’m of the “assume the cow is a sphere” school of engineering. 