Maximum tensile strength of M6 A4 (316) bolt?

[Ian_Edwards]

Does anyone know what the maximum tensile strength of an M6 bolt is?

I ask because the lifelines on my boat have M6 studding swaged onto the SS guard wires, these terminate in M6 A4 SS lifting eyes, effectively nuts. I then use a lashing to the pulpit to adjust the length of the guard wires.

I've done some research using Google and come up with answers as low as 2500N, approx 250kg force, this seems very low and would probably be the weakest link in the guard wire chain.

Is this correct?

One for the mechanical engineers?

 

[pvb]

I've done some research using Google and come up with answers as low as 2500N, approx 250kg force, this seems very low and would probably be the weakest link in the guard wire chain.

You can find figures as high as 9000N. What's the diameter and construction of your guardrail wire?

 

[jdc]

Does anyone know what the maximum tensile strength of an M6 bolt is?
... answers as low as 2500N, approx 250kg force, this seems very low ...

It's about right. But what you have to take into account is that this number includes a factor of about 5 to allow for fatigue, so the ultimate strength, which is what you care about, is more like 1.25 tonnes.

This can be put into context: lifelines have to have a breaking strength of 2 tonnes, and some reckon 3. But that's becuase a snatch load is usually given a safety factor of 12 or more.

I've 6mm stainless swaged terminals on my guard wires and have no worries about them. I put my weight on them quite frequently.

 

[jakeroyd]

I would echo the advice given above.
An M6 A4 bolt has a tensile load of about 9kN at 0.2% yield but bear in mind this is in yield (ie. it has failed as a system and has supported only one application of this load.

You rigging bolts are subject to fatigue loads and cyclic loads and therefore the actual load you should be considering is the endurance load (or stress).
A fixing with a stress lower than it's endurance stress effectively has a fatigue life of infinity (excluding other effects like corrosion and miss assembly etc.)

The axial dynamic load is given as about 1.4kN , the data I looked at did not say this would be below the endurance limit but I would guess that it would be.
To understand this force it's still close to 1.5 metric tonnes.

 

[thinwater]

If it is stainless, don't we have to assume it is lower strength? Additionally, high strength steels cannot be swagged. Thus we would use 500 MPa, 20.1 mm^2, or about 10KN minimum tensile strength. I'm pretty sure none of the marine parts are high strength steels.

The standard (World Sailing) calls for 4mm wire (boats up to 13M), which has a BS of 8-12KN, depending on the grade and braid. World Sailing, curiously, does not specify strength, only diameter.

Many US wires us 1/4-inch bolts (in 316 SS that is 2100 pounds min tensile strength, or about 9.3 KN.
This lifeline turnbuckle, from a reputable maker, has a breaking strength of 2500 pounds (11KN).

Thus, everything seems to match, including the OP's estimate of 11.1 KN.

Calculating the actual impact force of a falling body is very complicated, in part because the stanchions will bend (this has been proven both in the field and in testing). The concerns are corrosion and fatigue at the fittings or stanchion holes--that is where the failures happen.

You can always go oversize, but fitting the swages through the stanchion holes may be a problem.

 

[Norman_E]

My guard wires were replaced last year, 4mm wire is terminated with an 8mm swaged stud, not 6mm, and the stud passes easily through the stanchions.