hey guys i have been researching frames a little and i was thinking
1. How does the factory test there frames before they release a car honda,mini, suzuki ford etc
2. What does an engineer look for when they veiw ppls cars that have had engine conversions done, i mean they view them but how do they know there good or not what do they look for

i know there is one or two engineers on here ??

Frames are usually tested on a very accurate simulator before they are physically produced. Im pretty sure once they are past the simulated crash testing (on computer) they produce the car and move onto real world crash testing.

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No more Minis!......For now.

their are some pretty complex mathmatical equations to size and design a frame. It's not a great deal of fun. Most people use CAD and then some plug-in's and this will do it for you. Sorry for being vaige it's a pretty big feild and that's a non specific question

usually when an engineer looks at your frame he will check quality of welds. material thickness and will visually asses that it will be sufficent for the scope of modification. i.e. is it chunky and re-inforced

probably best to consult an engineer first if possible, some engineers like things done a particular way or they might not sign on it

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-doing a Degree in Mechanical Engineering,
and a few conversions:
13B Extend in a 1600
4EFTE in a mini ute (all slowly)

The engineer would normally want to see at least the following, in no particular order:

Is the final sub frame at least as strong as the original?
Is the final at least as rigid/stiff as the original?
Do the new engine mounts correctly transfer the new loads to the structure and then on to the mounts between the frame and the body?
Is the frame designed and constructed to minimise fatigue cracking?
Will the engine move excessively in the frame?
Does the frame compromise the integrity of other systems like the suspension, steering, brakes and other nearby items?
Does the frame contain members likely to break free and penetrate into the cabin in the event of a collision?
Are the welds full penetration and of sufficient area and quality for the task each performs?

To answer the strength and stiffness correctly would take some maths and probably software to assess very accurately. If you were to pay an engineering company to assess this properly because you were building something your life depended on, you'd pay about $20,000 to get a 3D FEA analysis done for all of the load cases. Then you'd pay about the same again for physical testing and a report. If you only pay an engineer say $600, then this only gives you about 4 hours work at current charge out rates. Therefore simplifications are used to give you an answer quickly. THese could be: does the new design have similar cross sectional area of steel and equivalent first moment of area? Are the original load paths replicated? (eg, is the front track rod mount still supported longitudinally when the frame is replaced by an up-and-over design?)

The weld strength and adequacy are similarly simplified. In a proper production environment, the welds would be accurately designed and specified, then the welds would be "qualified" and test welds would be broken and cut apart to be "macroed". Once proper technique was determined the welders doing the job would be certified to do each individual weld type. With car certification the engineer can only look at completed welds and make a judgement. To have some confidence they'll need to be good looking with obvious penetration into both components.

The fatigue issue is another simplification. Car companies design to reduce fatigue then test the cars to death for certainty. It was testing like this that led to minis having sub frames in the first place. The engineer will look for fatigue causing designs like sudden changes in stiffness caused by sudden changes in cross sectional area with no gussetting, stitch welding in components likely to flex, weld undercuts at the end of gussets, square edge cut outs in components likely to flex, point loads from fasteners through thin sheet and highly flexed items.

I've seen some dodgy stuff posted on this site that apparently has been approved by an engineer. Unfortunately, because of the simplifications used, there is a lot of personal judgement relied upon. The welding on the yellow subframe posted here is a bit on the "bird crap" side for my liking and the Daihatsu 3 cylinder frame has large chunks cut out with nothing put in to replace it. Then there are the frames that are stong but not stiff enough at the suspension mounting points that could lead to all sorts on unpredictable handling as the mounting points move under load.

There is a huge amount of work that goes into modern car design. In comparison, only a tiny amount of work goes into "engineering" a modified car. Some engineers are very cautious, not willing to risk your life and their career on your modification. These guys typically keep away from this type of work (me). At the other end of the scale, there are some real cowboys out there who'll let anything go and take the risk. Also, unfortuantely, there are some people with university degrees who don't have any furken idea about cars or real engineering. It is a bit of luck to find a reasonable engineer willing to certify your car for an affordable price who'll help you not kill yourself by making you change a couple of things.

M

AMEN to that brother... just a addition. Australia's rules are quite strick and not alway's the easiest to get around. This is in most cases a good thing.

however it is really an eye opener to se what's on the road in oter country's with clearlt less rules than Australia. some workmanship is amazing and others look like they were clearly put in overnight with left overs found in a garage.

I am much more worried about what happen's o/s sometimes

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-doing a Degree in Mechanical Engineering,
and a few conversions:
13B Extend in a 1600
4EFTE in a mini ute (all slowly)

yeh i realise that its involved and its was a fairly general question prob due to my lack of knowledge in the feild

surely testing the strength of a frame could be done on a machine which puts the related forces on it ????

You could always put forces onto your frame and yes that would test it, but what do you want to test? The maximum force that can be exerted onto the frame, or how the frame will go after 1000 mild forces? How do you know if after putting a certain force on it, the frame hasn't elongated at all (hookes law) in any direction. Where do you put this force that you speak of? How does the torque transfer through the frame? Its just not worth it for once off conversions like us. I think the latest SolidWorks has a FEA add-on which you can test forces with, i'm not sure about moments - pretty basic though i'm told but it would do the job. As long as you show to the engineer that you have supported the engine soundly and that the rigidity of the car hasn't altered too much you should be right. I think Mokesta has hit the nail on the head with the engineers questions, and then Over-Engineer to be safe.

Well I guess everyone has a right to there own opinion

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with the fury of a Monkey Dishwasher aimed at your Purple

57 Morris minor
88 Rover Mini