Verify what the recommended torque is for your specified thread diameter/pitch. In reusable bolted connections such as a wheel stud application, the maximum torque value should be such that the material is loaded to 90% of its yield. I'm guessing 80 ft-lbs, or possibly higher due to faulty torque wrench, is too much causing plastic deformation of the stud leading to early fatigue failure. A typical 7/16 stud only requires 65 ft-lbs max, assuming normal OEM stud material. Aftermarket studs will use different materials allowing higher torque values, giving higher clamp loads, while not plastically deforming the material.
1) As stated, the existing torque wrench is out of cal. GET A NEW ONE !!!! Oh, and USE it.
2) The statement "Aftermarket studs will use different materials allowing higher torque values" is not accurate. I switched from OEM studs (factory spec 100 lbs/ft) to ARP. Very quickly I broke studs. In speaking with ARP, they stated that the studs I installed should be torqued to 75-80. Problem solved.