...

The selection of materials for a rocket motor case is an interesting endeavourendeavor. Typical constraints are availability, cost, lead time, availability of appropriate casting tubes and liners, compatibility with commercial standards, etc. Find the main article here.

...

\sigma_HL = \frac{Pd}{4t}

Bolt Hole Tear Out Strength

...

There are some practical considerations as well. Empirical results show that to avoid tear out the bolt should be at least 1 bolt diameter from the edge or any other bolt in the pattern. In other materials it can be common to require that ratio to be 1.5 or 2.0 diameters from an edge or bolt. For additional reading please investigate AISC J 3.4.

...

Example Calculation Using Phoenix Booster Forward Closure

Image Added

Here is a side view of the phoenix forward closure. To make sure that the case will not fail under the motors pressure, we will calculate the shear stress of the forward closure. We will also calculate the tensile stress on the area in-between the bolts.

Distance 1 = 0.63 in

Distance 2 = 1.63 in

Distance 3 = 0.75 in

Using the equation from earlier, we can calculate what the shear stress due to the bolts will be. However since there are two distances from the holes to the edge of the case and we have an equal number of bolts on each row, we will average them to use in the equation.

Thickness of Wall = 0.25 in

A = 0.25*(1.63 + 0.63)/2 = 0.28 in^2

Now we can calculate the shear stress:

P = 826 PSI

d = 4 in

Num Bolts = 24

T_shear = (826*(4/2)^2*pi)/(24*2*0.28) = 772 PSI

This amount of shear is significantly lower than the shear modulus of aluminum, so this should not be a concern.