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Thread ID: 145903	2018-02-27 04:22:00	Truck-Trailer Quality Rant	Terry Porritt (14)	PC World Chat

Post ID	Timestamp	Content	User
1446782	2018-02-27 04:22:00	Here we go again, crass ignorance about matters relating to QA, this time complete ignorance about metallurgy/engineering. Truck-trailer towbars and couplings have been found to have cracks, with comments also about being under engineered. Failure of a coupling is obviously a disaster when a trailer goes careering out of control along a highway. We have the trucking industry downplaying the problem, and then the chief executive of The Road Transport Association thinks completely erroneously that cracks in tow bar is the same as a lawn mower wearing out.....idiot :angry Do these people not know anything technical ?????? Wearing out is caused by friction and wear...rubbing..fretting etc A topic that goes under the heading of Tribology. "Cracking in steels and metals, can be caused by faulty steel, non metallic inclusions: Non-metallic inclusions in steel are foreign substances. They disrupt the homogeneity of structure, so their influence on the mechanical and other properties can be considerable. During deformation, which occurs from flatting, forging, and stamping, non-metallic inclusions can cause cracks and fatigue failure in steel." en.wikipedia.org Then there is fatigue caused by repetitive alternating stress. There may be both aspects present, as well as poor choice of steels, or cowboy design and manufacture, DSIR in the old days would have sorted this out before they were even on the road :clap In the meantime we are all at risk of being side-swiped by a runaway trailer, not a nice idea. All he had to do was to read Wikipedia.....not too hard eh ?	Terry Porritt (14)
1446783	2018-02-27 06:11:00	www.stuff.co.nz http://pwe.co.nz/ Yes, a bit of denial there....shocking really.	piroska (17583)
1446784	2018-02-27 20:33:00	Me being a former NZ Govt IANZ (www.ianz.govt.nz/) accredited mechanical lab technician - and working with DSIR/Massey University, not all certified tests (and international recognized) are relevant to real working environmental loading conditions. Be it metals, plastics, or corrugated/carton board. In fact new "real world tests" need to be implemented at times....and testing differently too. Static testing vs dynamic testing (or destructive vs non destructive) need be developed - so as to measure durability of a product (often involving stress strain testing, -short and long term, then stats analysis relationships sometimes). This can take weeks and ramps up costing dramatically. Been there. I have tested products - and certified them based on most standard mechanical tests - but in a lab. But feedback from real world use showed failure So we developed new tests(s) and procedures which when lab tested indicated failure (one day simple "spot" tests then become about 3.5 weeks - laborious but relevant for a mix of products). Also test instruments need be precision calibrated, but at on more than one level (e.g. 6 months and 2 years - so as to pick up reliability/repeatably issues, or at different % loading). Some labs might not do that. Yet calibration (and hence certification) can occur (erroneously) for a specific parameter...rather than the full parameters.	kahawai chaser (3545)
1446785	2018-02-27 21:33:00	I see where you are coming from, used to be Telarc accredited too before IANZ. That was my job in DSIR Engineering Metrology and worked closely with the DSIR metallurgists, in fact worked closely with metallurgists all my working life including my boss for years. You have to start somewhere, and conformance to appropriate standards is the starting point. If materials and methods dont conform then you don't have any basis for confidence. Since all this steel will be imported, most likely from China, it is more than possible that the cheapest fake certified steel has been used, as it has elsewhere. Lab tests on the steel should be on the agenda. Probably no one remembers now the CNG Bogap gas cylinder scandals, cheap cost cutting Italian crap in that instance, and very dodgy acceptance by the MOT at the time despite failure to conform to gas cylinder standards.	Terry Porritt (14)
1446786	2018-02-28 01:16:00	You have to start somewhere, and conformance to appropriate standards is the starting point. If materials and methods dont conform then you don't have any basis for confidence. Lab tests on the steel should be on the agenda. . True - you are right about appropriate standards. You probably know ASTM, which we used extensively, but then there are also British, German, (DIN), and some Aussie/NZ standards .But as I was saying, some products can conform to tests but fail when in use certain conditions. We once spent 7 years developing a combo test apparatus (think pull-twist-accelerate, impact, vibrate, etc all at once). Scientists, Professors, Engineers, trials, etc, and 3 institutions all involved, at costing of over 150 k. Huge cost and resources.	kahawai chaser (3545)
1446787	2018-02-28 03:17:00	not all certified tests are relevant to real working environmental conditions. Yep.....thinking of engineers and their computer models...gigo....	piroska (17583)
1446788	2018-02-28 04:40:00	Yep.....thinking of engineers and their computer models...gigo.... We're not thinking necessarily of computer models, we are talking about standards and mechanical and metallurgical testing that have been in existence since for ever, even before main frame computers, but obviously updated over the years. Computer modelling for design and stress analysis, like finite element methods are obviously used, though I doubt it in this instance.	Terry Porritt (14)
1446789	2018-02-28 19:52:00	I see where you are coming from, used to be Telarc accredited too before IANZ . That was my job in DSIR Engineering Metrology and worked closely with the DSIR metallurgists, in fact worked closely with metallurgists all my working life including my boss for years . You have to start somewhere . . . Was that before the DSIR totally concentrated on making a cheap substitute for seawater? ;)	R2x1 (4628)
1446790	2018-03-01 03:10:00	Just another “Knee Jerk” reaction to “Media Hype” . :rolleyes: Let’s face it, Trailers, Trucks, Trains, Ships, Aeroplanes, Bridges, Railway Tracks, . . . . . . . . etc . all suffer from Metal Fatigue at some stage and cracks are certainly a sign . However, inspections are carried out on all of them and the problem repaired or replaced . I don’t think a Truck Trailer Tow-bar breaking, has ever killed or injured anyone in NZ, despite the huge workload expected of them . Regardless, the reality is that Doctors have killed or injured more people than run-away Trailers .	B.M. (505)
1446791	2018-03-01 03:23:00	There was a prime example of a truck-trailer bogey malfunction on the downhill stretch of Ngauranga Gorge this morning. No-one was hurt but it sure caused chaos. Read here (www.stuff.co.nz).	Zippity (58)
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