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Chapter 10: Problem 14

An expensive machine used in the fabrication of silicon computer chips requires that water be supplied for manufacturing purposes. The machine is designed and manufactured in Japan and installed in Texas. The on-site installation requires that a plumber connect the machine to a plant water source with copper pipe, metal fixtures, and a plastic coupling nut. A few days after installation, the nut fractures along a thread near a transition (stress concentration) and sprays water on the machine. The machine sustains extensive water damage during the incident. The installation instructions for the machine did not include specific directions, specifications, or warnings on installing the water supply system. Comment on the use of copper tubing, metal connectors, and a plastic coupling nut much like what you might find to connect a toilet to a home water supply.

Short Answer

Expert verified
The use of copper tubing, metal connectors, and a plastic coupling nut, while sufficient for residential applications, may not be appropriate in this industrial setting. The plastic nut wasn't suitable to handle the stress concentration near the transition and failed, causing extensive damage. The manufacturing company must provide specific instructions that account for such stress points and recommend the appropriate materials for every component of the water supply system.

Step by step solution

01

Analyzing Material Compatibility

We begin by analyzing the compatibility of different materials involved - copper tubing, metal connectors and a plastic coupling nut. It's important to understand that even though these materials may work perfectly fine in less-stressful environments like a residential water connection, they may not be suitable for industrial applications where the physical and thermal conditions are drastically different. Copper has sound mechanical properties and good corrosion resistance, making it suitable for carrying water. On the contrary, the metal connectors and plastic coupling nut, if not made from suitable materials, can be a weak link.
02

Stress Concentration and Failure Analysis

Expect a higher level of stress near transitions - the places where different materials or components meet. In this scenario, the plastic nut failed near a transition, indicating that it couldn't bear the stress concentration. The thread of the coupling nut becomes a stress riser, the point of high stress concentration, because of the discontinuity in the material, leading to the fracture.
03

Evaluating the Installation Instructions

Lastly, evaluate the installation instructions provided by the Japanese manufacture. The lack of specific directions or warnings for the water supply system could indicate, in part, that the company didn't anticipate the possible failure at that connection. This was a point of potential risk, and its lack of attention might have contributed to the nut's fracture and consequent damage to the machine.

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Most popular questions from this chapter

Two aluminum plates, which are part of an aircraft structure, are held together by a grade \(7, \frac{1}{2}\)-in. UNF bolt. The effective area of the aluminum plates in compression is estimated to be 12 times the cross-sectional area of the steel bolt. The bolt is initially tightened to \(90 \%\) of its proof strength. Gust loads, varying from zero to \(P\), tend to pull the plates apart (this results in negligible bolt bending). With a safety factor of \(1.3\), what is the maximum value of \(P\) that will not cause eventual bolt fatigue failure? What clamping force will remain when this value of \(P\) acts?

Two parts of a machine are held together by bolts, each of which carries a static tensile load of \(3100 \mathrm{~N}\). (a) What size of class \(5.8\) coarse-thread metric bolt is required using a safety factor of 4 (based on proof strength)? (b) What is the least number of threads that must be engaged for the thread shear strength to be equal to the bolt tensile strength if the nuts are made of steel whose yield and proof strengths are 70 percent those of the bolt steel?

A square-threaded power screw with single thread is used to raise a load of \(12,500 \mathrm{lb}\). The screw has a mean diameter of 1 in. and four threads per inch. The collar mean diameter is \(1.5\) in. The coefficient of friction is estimated as \(0.1\) for both the thread and the collar. (a) What is the major diameter of the screw? (b) Estimate the screw torque required to raise the load. (c) If collar friction is eliminated, what minimum value of thread coefficient of friction is needed to prevent the screw from overhauling?

A jack similar to the ones shown in Figure \(10.5\) uses a single square-thread screw to raise a load of \(50 \mathrm{kN}\). The screw has a major diameter of \(36 \mathrm{~mm}\) and a pitch of \(6 \mathrm{~mm}\). The thrust collar mean diameter is \(80 \mathrm{~mm}\). Running friction coefficients are estimated to be \(0.15\) for the screw and \(0.12\) for the collar: (a) Determine the thread depth and helix angle. (b) Estimate the starting torque for raising and lowering the load. (c) Estimate the efficiency of the jack for raising the load. (d) Estimate the power required to drive the screw at a constant one revolution per second.

Review the web site http://www.nutty.com, and list the different kinds of (a) nuts, (b) bolts, and (c) washers. Comment on how to evaluate the products promoted on a web site.
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