HW NEED HELP

Data

• April 1966 US Army Gun No 733 failed catastrophically.

• Made out of a high strength steel alloy, it broke into 29 pieces, hurled over distances up to 1.25km from the firing site

• First gun to fail in this way – prior designs were failing by wear and erosion of the barrel bore.

HW Data

• din=17.8cm dout=37.3cm

• L=10.5 m

• At the time of failure the gun was being fired at 2 minute intervals with a nominal pressure of 345 MPa

• The gun has experienced 373 rounds of 345 MPa and 227 rounds of 152 MPa

This is how it broke.

Semi elliptic crack

half minor axis=0.94cm

major axis=2.79cm

This is how is should

break (leak before break)

MATERIAL 4335 Steel with modified Cr and Mo content and 0.14% V

Axial (if closed)

Hoop

Radial

t=thickness

c=semiaxis along cylinder length

a=semiaxis along thickness

Possible reasons

• Overpressure

• Environmental effects

• Rate of loading

• HEAT CHECKING  network of cracks with a depth of ~0.13 cm

Residual stresses

Residual stress measurement hole drilling ASTM Standard E837

Make a hole Monitor the change of diameters via strain gauges Back calculated the stresses from strains (not trivial)

Assuming that hole drilling does not affect the material locally

Similar in theory are the slit method and the curvature methods

Residual stress measurement X-ray • Stress is an extrinsic property so it must be measured indirectly

Need modulus, Poisson

Similarly with neutron diffraction and to greater depth and accuracy (and cost)

Not from the same cannon but it indicates clearly that the true residual stress is much lower than the 60% of yield stress that the analysis shows. ASSUME ~200MPa compressive