deevlash wrote:stress is an engineering term, stress=F/A and is measured in MPa (mega pascals) stress cant be measured itself but is usually worked out from measurements of strain and knowledge of elastic properties of the material. There are different types of stress which could have caused the failure, such as torsional, but probably tensile in this case. The bridge could have failed due to fatigue as opposed to a stress fracture or any one of a number of reasons. The reason they dont go into this level of detail is that it confuses people who spell "surely" as "shurly".
Ah the spelling nazi strikes again! you would think that you might have learnt your lesson after being slagged off for berating Cupcake or do you get your kicks out of trying to wind people up? Looking at those posts you don’t seem to be immune from the odd mistake yourself. I never realised that you have to spell perfectly to be allowed to express an opinion!
Why don’t you spend more time thinking more about the kwality (appreciated Soceceroo) of your posts and not playing at being a primary school teacher? If you want to try and educate people in a topic you clearly have little idea about, go a read a basic book on failure analysis before you try. Wikipedia doesn’t have all the answers, I take it that was where you got your information from? I was pointing out that the statement “stress fracture” is meaningless in engineering terms, to break something ie fracture it, you need to apply stress, therefore all fractures could be described as stress fractures. A fatigue failure is a stress fracture because you have to apply a cyclic stress to fracture the item.
If you had been bothered to read the thread you would seen that there had been some good discussion on the possible failure modes (source of the stress ie fatigue, overload etc) and the root causes of the failure (why the stress was excessive for the component ie poor design, casting quality). That discussion including fatigue and the likely possibility that the original casting were defective due to QA issues.
What I really would be interested in seeing is a copy of the failure investigation report, as council tax payers I think we should be credited with a bit of intelligence and allowed to see the facts rather than being drip fed the odd titbit by journalists who don’t have any engineering knowledge and therefore use terms like “stress fracture” which is more commonly applied in medical fields (look it up in Wikipedia)
By the way, you do not need to know anything about the elastic behaviour of a material to measure stress, your equation shows that clearly, all you need is applied force and area. Have you ever done a basic tensile test on a piece of metal? When you do need to know about the elastic behaviour, is when you use strain gauges to measure deflection and then calculate the stress that a structures is under.
Going back to “shurly” I’m a mite embarrassed, why can’t HG have a built in spell check? I promise to spell check all my future posts if you promise to stop being so anally retentive! Truce? I’m joking about the HG spell check by the way, I’m a great believer that if a reader can understand the text regardless of spelling, then the writer has communicated effectively. Languages evolve and spelling changes, I hear there is a move to phonetic spelling and surely shurly will have its day!