Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.
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Two Discussions on Electromagnetic Materials and Sealing Medical Gases

By Jeff Wickham, P.E.
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Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.

Q: What are the best materials for electromagnetic applications? A: This depends on the application, and on factors such as the performance, cost and specific geometry. Electromagnetic materials are commonly compared using B-H curves (B stands for induction and H for magnetizing force), which are basically a plot of how much magnetic flux a material will carry versus the intensity of the magnetic field. This can be experimentally seen by using an electromagnet and observing how strong…

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Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.
Ask the Engineer

Two Discussions on Cantilevered Snap Fit and Calculating Max Shear Stress

By Jeff Wickham, P.E.
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Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.

Q: I designed a cantilevered snap fit that extended as a continuation of a wall, but some of the prototypes cracked at the snap finger barb. Usually, the highest stresses are at the base of the cantilever. So why did the snap finger crack where it did? A: The snap finger would likely have cracked at its base if it were extending from a flat surface rather than as a continuation of a wall.  In this case, because it was extending from a wall there was no stress concentration at the base,…

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Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.
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Three Discussions on Bonding a nylon component to an SLA part, First production run of an impeller assembly, and Plastic part with bosses for screws

By Jeff Wickham, P.E.
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Jeff Wickham, P.E. is the Principal at LifeHope Medical, Inc.

Q: I tried to bond a nylon component to an SLA part, but the adhesive easily peeled off of the nylon even though I used what I thought was a very good adhesive. Any recommendations on how to get these parts bonded together? A: Plastics have different characteristics based on whether their material structure is semi-crystalline or amorphous. Plastics are composed of long polymer chains. In an amorphous structure these polymer chains are tangled together like a plate of spaghetti noodles. Typical ex…

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