Design News for Mechanical and Design Engineers

I PAY, YOU PAY, WE ALL PAY

Philip M. Piper DESIGN NEWS READER

Field's response: I'm sorry, what was I thinking? I forgot that the movie industry (and the recording industry too!) charges monopoly rents on everything they produce. So even if they find a way to save money, of course prices will go up! But in response to your letter, I can personally think of lots of things that aren't paid for by me since I do not choose to buy them. That will certainly be the case with digital cinema if theaters raise ticket prices to cover costs. I'll wait for the DVD. Or, better yet, I'll read the book.

My congratulations to Rose McCallen of the Lawrence Livermore National Lab and her project to improve the aerodynamics of trucks to reduce drag and improve fuel economy. It sounds like a much-needed endeavor! The description of her work, (DN B.M.O.C. 8.04.03) was very interesting. It occurred to me that she might find a way to eliminate one of my pet peeves about trucks (and make a better world for everybody at the same time). When it is raining and/or there is water on the road surface, tractor-trailer rigs tend to throw up huge amounts of water into the air because of their multiple, unshielded, wheels and tires. The resulting water-cloud surrounding the truck drastically reduces visibility, and makes it difficult, annoying, and dangerous to pass the truck. This is especially true on two-lane roads. I suggest that, if she could find a way to redirect the aerodynamic flow-field around trucks to reduce or eliminate the water-clouds, you could make our highways safer and do a favor for all automobile travelers. Think about it!

Donald S. Freeman DESIGN NEWS READER

McCallen's response: We are starting a new effort in the coming fiscal year (starting Oct. 1) to understand the mechanisms of splash and spray due to the turning wheels on a heavy vehicle that will lead to the smart design of mitigation devices. A report soon to be posted on our website with the results of our May Working Group meeting may have some information of interest. The website address is http://en-env.llnl.gov/aerodrag/.

After reading "The Case of the Mangled Main," (DN Calamities, 08.04.03), in which you discuss the fracture of a cast iron gas main, I immediately sensed that something was "wrong." The fact that the "chevron" artifacts on the fracture surfaces pointed to the bottom of the pipe as being the fracture origin site, and the conclusion that frost heave was the approximate cause of the failure, are inconsistent. Given that circumstance, the bottom of the pipe would have been in compression—an unlikely condition for the origin of a fracture. I discussed this case with my son, a geotech engineer. He assured me that a frost heave would have caused the pipe to bend upward, thus putting the bottom in compression. It seems to me that a compression load, particularly an impulsive or impact load, on top of the pipe would make more sense as the cause of rupture.

Bill Glater DESIGN NEWS READER

Russell's response: I agree that a frost heave directly under the region of fracture would have put the top of the pipe in tension. Any fracture would then have started at the top and the chevrons would have been the reverse of those observed. I believe that the heaving force was to one side of the fracture. This would have put the bottom of the region that fractured in tension. The top part of the pipe just over the force would have been in tension. It was then a question of which region in tension would fracture first. The graphitization was very uneven. I am convinced that the severity of the graphitization near the bottom of the observed fracture combined with a tensile force to give fracture. Had the most severe graphitization occurred at the top of the pipe just over the heave, I believe there would have been a tensile fracture starting at the top of the pipe. Our geotechnical engineers considered failure due to a surface force to be unlikely. They could, of course, have been wrong. Thanks for your carefully considered response. Such comments by readers make writing the column enjoyable. At the same time they have taught me to be very careful about just how I express myself!

I read with interest Larry Zirkle's article "The Case of the Corked Bat" (DN 09.08.03). Up until now, I had yet to see a proper explanation of the benefit of one of those. Larry comes close to the answer in the second to last paragraph, in which he discusses conservation of angular momentum. In my opinion, the corked bat is like an oversize Prince tennis racket with a larger "sweet spot" but no extra weight. Sammy Sosa gets the benefit of the larger sweet spot on the big bat, but he can get it around quicker because of the light weight. I think the benefit is real, and Sammy, Albert Bell, and others have been using them for years with real results.

David Blake BILLERICA, MA

Your pointing out that ladder construction improvements came out of legal activity (The Case of the Beneficial Barristers, DN 08.18.03) is the first time I have thought positively about malpractice suits. It wasn't OSHA that improved ladder design, after all! At the same time, you produced an absolutely accurate description of the two extension ladders I purchased 24 and 4 years ago from consumer discount chains. The 24-year-old 20-footer is flimsy and shaky—and light in weight. It finally broke into two pieces after it folded where the circular step broke free from one rail. I now use both sections only intermittently (and carefully), as an attic ladder and for trimming 8-ft evergreens. The much newer 20-footer weighs at least twice as much, but I can eat my lunch on the top rung without holding on!

Dave Weigand DESIGN NEWS READER

I liked your Beneficial Barristers column in Design News. I suppose that since I am under the load limit I have less to worry about than others, but I do look at it all before I go up. So is this all necessary to protect the desire of the firm to sell yet-lower priced ladder? I suppose so. The standards process has not been completely effective, so an occasional shot across the bow keeps us honest. I do recall previous efforts to provide quality control in medicine. The peer review system collapsed as everyone peer-reviewed out-sued those on the committee. It left both the ambulance-chasing lawyer and the malpractice insurer in the business of quality control in medicine. Cancellation of the insurance policy of the malefactor has been possibly the other quality control mechanism that works. You can argue and contest with OSHA, but if Factory Mutual says that the improved stuff is necessary to keep your policy, it gets done. I have seen this work effectively in medicine and industry.

Owen Gallagher HUDSON, MA

Nice article on ladders. Today the safety aspects are wholly reinforced by the warning stickers attached. In 1974, having just completed my junior year of ME school (Pitt), I took my girlfriend on a ride on the little Ferris wheel that showed up at the carnival at the local shopping mall. To my amazement the two of us were riding in a heavy steel seat (i.e. bucket) swiveling in two 1/2-inch-diameter shafts that passed through bushings on the main wheels (left side of bucket and right side of bucket). There was considerable distance between the shaft attachment at the bucket, and the bushing edge on each wheel. Having just finished a course in Materials Mechanics where we pulled and sheared lots of metallic samples to destruction, I immediately feared for my life. I guess it takes years of exposure to metal failures before you can foresee all of the potential hazards by "eyeball".

Ray Minich BRADFORD, PA

I recently watched three construction workers ascend what had to be a 28-ft ladder, extended way beyond what I would consider a safe level. To quote you, it did indeed take "a frightening lateral bow." They paid no mind to such. I had to quit watching. Too bad OSHA was not passing by. Always enjoy your articles.

Martin Whitehurst BURLINGTON, NC

Regarding your ladder piece, is anyone manufacturing long, light ladders of exotic (carbon fiber, etc.) materials?

Arnemann Grender PIKEVILLE, KY

Russell's response: My younger son suggested I title the faulty aluminum ladder piece "Unsafe At Any Height" but it wouldn't quite fly. So "Beneficial Barristers" it was. Thanks for your response. You brought up things I had not thought of. My piece stated that the aluminum ladders of forty years ago were death traps and that the ladders of today are much safer. I attributed this change to plaintiff lawyers extracting large settlements from those responsible for the manufacture and distribution of the unsafe ladders. You writers have given other contributions to the improvement. Dave Weigand points to OSHA forcing the changes that allow him to eat his lunch on the top rung of a modern ladder. Owen Gallagher notes that the threat of insurance cancellation gets action where standards and peer review have failed. Ray Minich points to better warning stickers on modern ladders. I agree with all of you. Martin Whitehurst tells of witnessing three people at a time climbing a 28-ft aluminum ladder. There was no failure in spite of a horrific deflection. It must have been a recent ladder as the old ones would certainly have collapsed. Arneman Grender asks about use of exotic materials, such as carbon fiber. A carbon fiber-epoxy ladder would be wonderful to use, but also wonderfully expensive. I have heard of magnesium ladders, which apparently have some fairly modest advantages over aluminum. Again, thanks for writing.