On this one, the p/u truck was under the semi trailer, no roll over just straight ahead,I was part of the cleanup crew.I was impressed with the lack of damage to the trailer,other than the gooseneck being bent and the horse dividers being severely bent.It was difficult to remove the bodies,the p/u truck was literally demolished,death was guick for the victims.

 

Perhaps even more important than ductility (measured as % elongation) is the difference in hardness between the Grade 5 and Grade 8 fastener. The harder Grade 8 fastener will typically be more susceptable to cracking and fracture from notch sensitivity and/or corrosion than will the softer Grade 5 fastener.

As I said, if the engineers selected Grade 5 fasteners, cost was not necessarily the driving factor. I'd be careful making a "knee-jerk" decision to automatically replace the Grade 5 fasteners with Grade 8.

Rusty

 

BUt grade 5 bolts will shear and snap before grade 8 bolts start to bend. LInk is pretty technical I would advise looking into it before stating grade 8 will just snap and grade 5 bolts will bend but not break off. Sometimes manufactureres are cheap, like cutting corners and thats how they do it. Thinner guage metal, lower grade bolts and fasteners, using plastic, overseas labor, etc etc the list goes on.

 

Not if more or larger Grade 5 bolts have been used to achieve equivalent clamping force. That's how an engineer will apply Grade 5 fasteners to take advantage of their ductility and better resistance to corrosion cracking.

Rusty

 

Well anyway you look at it, grade 8 bolts are better for the job, stronger in every way compared to a similar grade 5 bolt and brittleness is not grade 8, to get a bolt to be less ductile and one that will not bend before braking you need to pass 180,000psi rating. Grade 5 is 120,000psi, grade 8 is 150,000psi. So grade 8 would not be much less ductile than grade 5.

 

I'm an engineering manager who has worked for an engine, compressor, gas turbine and turbocharger manufacturer for 31 years. I've shared with you how designers can select and utilize more ductile fasteners when ductility and lower notch sensitivity are desired without sacrificing any clamping force/joint strength. Whether you choose to accept that or not is up to you.

Rusty

 

Rusty, I read the article and also understand the credentials you present on your behalf and what it is you are trying to say however all the 5th wheel mounts we have ever installed were with Gr8 hardware. Kenworth trucks actually come out of the factory with Huck bolts that we were told are harder than Gr8 and a higher clamping force by design. So my question to you would then be if a Gr8 bolt was fastened tight on a frame mount with a corrosion resistant compound protecting it would it not be in the same size bolt a stronger connection. I was also taught to make a hole only as large as needed to make the hardware fit snug to prevent any unnecessary movement, thus reducing or preventing "notching". On a less serious note "What is the most feared words in the oil patch- HI I am an engineer and I am here to help". Okay so here it is proclaiming to be an engineer as much needed as they are does not instill a lot of confidence in the average layman who has been exposed to too many non-hands on experts who never worked in the field with real tools. Please try and understand where our frustration is created from. PK

 

Well, IMHO, I'm a different breed of engineer than you describe. I actually prefer hands-on work and started with my company as a Field Service Representative in 1973 before migrating to the home office. In addition to installing and commissioning new and remanufactured units, I ran the engine/compressor analyzer, performed vibration analysis, diagnostic troubleshooting and serviced electronic and pneumatic control systems (I worked for Honeywell for 3.5 years before having brain fade and coming back to the oil field where I grew up). I service my own vehicles, including motorcycles and my RVs, have built drag racers and SCCA Production-class race cars, so I think that I'm a pretty real-world, hands-on individual for an engineer. I wouldn't paint all of us with the same brush.

I have no problem at all with Grade 8 (or harder) bolts. The only point I've been trying to make throughout this discussion is that designers have many design criteria that they're trying to meet when they design a bolted joint. Sometimes we will use (let's say) 12 each Grade 5 fasteners in a design instead of 8 each Grade 8 fasteners. In that case, we will get equivalent clamping force and can take advantage of certain attributes of the softer Grade 5 fastener. In such a case, it's not always a good idea to look at the Grade 5 fasteners, say "Well, the designer was just being cheap!" and automatically replace them with Grade 8 or better (in actuality, the design using 12 fasteners is likely more costly to manufacture!) If the Grade 8 replacements are torqued close to yield (as they should be in critical applications to obtain enough prestress to prevent loosening in high vibration or cyclically loaded environments), then the clamping force will be much higher than that of properly-prestressed Grade 5 fasteners that the joint was designed to utilize, and that can cause other problems. Been there, done that, got the T-shirt in many years of analyzing field failures.

All I'm encouraging is for individuals to take a systems approach to analyzing these situations and to think before automatically running to the Grade 8 fastener drawer.

Rusty

 

"Well, IMHO, I'm a different breed of engineer than you describe."

Rusty: are you an engineer ? Did you go to school and study engineering ?

 

Yes, I did. Why do you ask?

Rusty

 

With the amount of law suits today. I would think that the manufactors that are selling these hitches have done more than just spec a bolt for a hitch. And as long as 5th wheel hitches have been around, simple stats from accidents should help prove it. I'm not an engineer. Me, I would put in the specd bolt. In the event of an accident, you can show the hitch was mounted with the specified bolts per the manufactors instructions. One less thing the DOT officer can shake is head about, if you survive.

TOW SAFE!!!

 

Rusty you are 100% correct in the system analysis and it is quite true that by increasing the strength in one area (Gr8 bolts) that another area will comprimise under stress and fail. Like I said we were taught to use the better bolt on frame rail applications and this like your field experience carries through from one experience to another. Great discussion with hopes that it makes other's think about the larger picture when working with projects and making blanket statements about issues. I do not have the technical background education you do but part of my job is to analyze failures that are incident related. The original question starting this thread poses an interesting thought, is the salesman selling you the consumer educated enough to get a customer equipped with the safest vs the best buy on coupling equipment. Will the customer even consider what will happen with bargains vs good choice in this event- glad somebody poised the question. If out of all this discussion 2 people change the way they think about their equipment and related purchases it is all worth while. PK

 

Side note: I think the biggest mistake is listening to salesmen. Research your info from more than one source.

Example: How many 25+ ft RV's are running down the road with an under weight suv pulling it. TO MANY. I watched a caravan pull a 26ft TT down the road, what caught my eye was the rear was about 3ft in the air. He had to crank the hell out of the weight distribution bars to get weight to the front wheels for traction. I know this because when he passed a weigh station by the house, MODOT shut him down. He said quote: "the (name left out) RV dealer said it would pull it".

 

And there in lies a lot of the problem.

 

"With the amount of law suits today. I would think that the manufactors that are selling these hitches have done more than just spec a bolt for a hitch. And as long as 5th wheel hitches have been around, simple stats from accidents should help prove it. I'm not an engineer. Me, I would put in the specd bolt. In the event of an accident, you can show the hitch was mounted with the specified bolts per the manufactors instructions. One less thing the DOT officer can shake is head about, if you survive. "

Can I correct a commonly quoted misconception ? people keep saying the you'll get sued if something you build causes an accident. However, the truth is, If you have insurance, you can't really be sued for an accident you cause.

Your insurance company protects you from liability unless it is criminal and therefore cannot sue you. That is why they call it insurance. If your insurance company could sue you, what would be the point of having insurance.

Lets say you install your hitch with a grade 5 bolt and it breaks and does damage to someone or something. And the damaged party sues. You are protected against your error by the insurance company to the limit of their liability. And the insurance company cannot sue you.

I know of two cases where bonehead people have made mistakes with trucks that caused damage and their changes were partially the cause. In no case did the insurance company sue them. They can't. One guy burnt his camper to the ground because his improper propane line leaked. They just asked him if it was arson and then paid him out.

rusty: I was just curious how you knew so much about bolts.