Hi Brent,
I'm not an engineer either friend, just trying to make sense of stuff to form an opinion I can call my own with a degree of confidence and understanding to support it. Two guys talking. Lots more listening.
Tragically, the image of the forces present when that welder came loose hit close to home. I hit the ditch in a similar fashion in a company service rig, my welder was however bolted down, and while the welder held on tight, the capped bottles came loose in there clamping. The outcome not as serious or tragic as the young man who lost his life.
When I fastened down my Ranger 9 years later back in the day to my truck bed, they were 3/8 grade 5 bolts no doubt in my mind. Grade 8's cost to much. Large washers on the underside due to the risk of pulling out after the scare. But I wasn't thinking mechanical properties either?
Between us, I think 4 , 3/8" grade 5 bolts were called for minimum. Frame had 4 - 3/8" holes and the manual said to mount securely. They didn't however say much more. I do use grade 8 bolts in my tow bar without any issues, pivot points, receiver location and mounting hardware. I didn't cheap out there thinking I had a greater risk of liability to be responsible for protecting against when transporting car projects on the cheap. My bolt guy said use grade 8's.
At the end of the day, what matters most is the message of ensuring personal and public safety by securing the welder to the transport.
The conversation that results is the education of understanding it would you think?
Higher point of shear and probability of shear now has me thinking so to gain understanding, satisfy the listeners, the higher point of shear would be related to tensile strength?
Higher probability of shear would be related to hardness? Are we thinking alike?
I could see where the grade 5 while yielding at a lower applied force, could be ductile enough to stretch over the limit in duration a higher strain is being applied. Is that a dazzel of brilliance or flawed thinking?
Hows that for a sentence? Did it make any sense? Sometimes I'm not sure if I'm trying to convince myself or confuse myself? I would think when looking at loading it would be a shock to the fastener.
However, I'm not sure I accept your way of thinking brittleness in this useage? I just wouldn't describe a grade 8 bolt as being more brittle, harder maybe? Tougher? I just wouldn't have used brittle.
I did however do a quick google search on this grade 5 grade 8 topic.
And your right on when you say, bolt them down.
Grade 8 is seemingly like insurance, more is better. But a grade 5 is enough in most cases. Internet can't be wrong right?
Just after reading your post, pictures flashed over the evening news. I caught the news report, more rain forecasted. Major flooding and wash outs... Prayers are with you folks.