Talks on truck towbars follow fatal crashes

Press, 31 August 1989, Page 14

Talks on truck towbars follow fatal crashes

PA Wellington Engineers from throughout New Zealand will meet in Auckland tomorrow to review steps taken to counter the use of defective Australian steel in towbars for truck trailers.

Ministry of Transport inspectors are still tracing all the owners of up to 100 trucks with towbars in danger of suffering metal fatigue and failing without warning. The chairman of the Institute of Professional Engineers mechanical engineering group, Mr Richard Bould, of Auckland, said a "potentially catastrophic” situation of loaded trailers breaking free while travelling at speed could have arisen. Engineers and road safety scientists started investigating • the problem when a series of multiple fatalities tipped them off to a potential problem with metal fatigue in truck towbars.

But they say the problem appears to have been stopped from recurring by the Australian steel manufacturer switching in April last year from using strip feedstock to better quality continuous-cast billets in making the high-tensile steel.

The engineers said towbars were the main danger area because although the defective steel had high strength, it was also very brittle and prone to metal fatigue. A Ministry of Transport engineer, Mr Dick Reynolds, said yesterday the problem was at the stage of a mopping-up operation from his point of view. Although there had been a great danger, theoretically, this had not yet been borne out by a risejin deaths from accident involving runaway

trailers, although there was a sufficient variation in mileages and loadings on New Zealand truck and trailer units for it to have started showing up. Most of the accidents investigated for this cause had involved defects in design, manufacturing or repair rather than metal fatigue alone. One such case, in which two or three people died at Ngaruawahia, was caused by metal fatigue initiated when a bush was tacked in place in a towbar with a spot weld, which led to a crack and eventual fracture, Mr Reynolds said. The problem had been spotted in New Zealand rather than Australia because a smaller proportion of Australian truckers towed trailers rather than using a tractor unit and semitrailer.

Another engineer who researched the problem, Mr Dave Mcßobie, said the metal fatigue was apparently mainly a problem on truck towbars because if they failed it was often under load and at speed. Other isolated failures had involved farm equipment which tended to break in the middle of a paddock without endangering other people. Engineers were not sure when the steel implicated in such brittle failures began entering New Zealand, but were sure the manufacturer’s change of fedstock last year had resulted in better quantity. Delegates to the Friday workshop at the Manukau conference centre of the Heavy Engineering Research Association on the new New Zealand standard code of practice for truck drawbars will be told of tighter rules which now govern the procedure for certifying engineers to perform inspections?