Fasteners that provide their clamping force below the yield point (all ARP fasteners work this way; this thread is inconclusive about which stock Mustang head bolts are non-tty -- at least 4 different opinions have been offered about the year break) can be used more than once. Tightening them to the torque point does not yield them - they simply act like a spring that 'springs' completely back to their original shape once the torque is removed. Measure them before and after torquing, and they are exactly the same length.
Torque to yield bolts are called that because the process of tightening them actually yields the metal - that is it stresses the metal PAST it's yield point. If you were to measure their length before and after torquing them in the proper way, they are longer after they're torqued - they literally are stretched and cannot 'spring' back to their original shape/length. Once yielded, TTY BOLTS CANNNOT BE USED AGAIN SAFELY - they are not capable of providing the clamping force needed to secure the component.
Torque to yield bolts are called that because the process of tightening them actually yields the metal - that is it stresses the metal PAST it's yield point. If you were to measure their length before and after torquing them in the proper way, they are longer after they're torqued - they literally are stretched and cannot 'spring' back to their original shape/length. Once yielded, TTY BOLTS CANNNOT BE USED AGAIN SAFELY - they are not capable of providing the clamping force needed to secure the component.