Show me the Inconel bolts on a car. You are trying to confuse the point.
Then show me the titanium bolts on a production vehicle. Or the bronze bolts. Or the aluminum bolts. deliberate obfuscation!

Steel, from the lowest 1015HR to 4340 has a modulus of elasticity of 29 million, plus/minus one million, at 70 degrees F. Aluminum is about 13 million. Gray cast iron is about 20 million and nodular is quite close to steel. It's not rocket science, it IS knowledge that a decently educated mechanical engineer should have in his brain.

AndyF is completely right. The fasteners we call bolts or capscrews are, in most of the uses we care about, used as springs. They exert a clamping force proportional to how much they are stretched, the cross sectional area and the modulus of elasticity. Very rarely do we see a modern fastener loaded in shear.

Another common misunderstanding is the number of cycles a bolt experiences. This will be hard to swallow for some of you. IF the bolt is properly designed and properly torqued (stretched), as long as the bolt does not see a stress greater than the stress from the torqueing, the bolt doesn't see any cycles. For heating, as long as the bolt isn't heated into the stress-relieving band of temperatures, that doesn't have an effect either.

Regarding Mercedes-Benz and the torque to yield bolt, my 1975 M110 engine has torque to yield rod bolts. The factory service manual has a simple procedure to determine if they can be reused. Use a caliper and measure the minimum diameter of the necked down portion. If it is above the specified diameter, the bolt is reused. I admit I was just a little bit uneasy the first time I took my self rebuilt engine and buzzed it to 6500 rpm, but the principle held, as did the rod bolts. The concept of torque to yield bolts is that when they have yielded they are exerting as much clamping force as they can. So no pussyfooting about deciding whether 80 percent of yield or 90 percent of yield is a good value, just torque'em until they stretch. Why do we replace so many now? Maybe on a $35,000 car or a $75,000 pickup the bolts are a minor expenditure.

Regarding throwing away bolts that have not failed in service - I believe it increases your risk. The reason is that the bolt served the purpose well. If they had failed you'd know about it. Now put in new bolts and they are back to being unknown quantities. I guess if they torque up properly they are probably good. But, don't fool yourself that you have lessened the risk. If the FSM says replace them then of course do it. But I have never replaced a main bearing bolt, and very few rod bolts. I have replaced a lot of exhaust manifold bolts and studs due to damage.

So I want to see some aluminum bolts from a passenger car. Maybe Feets knows where they are. I guess I'm still in the iron age.

R.