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Product failure

  1. May 15, 2005 #1

    Astronuc

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    I had the delightful experience of a couple of product failures today. Just thought I'd pass along a couple of observations from the field.

    First - while doing some gardening, my wife called out that the washing machine had just died. We had some work done it under warantee about 5 months ago. The machine is a front-loading design by Frigidaire. The front-loading designs use less water, and therefore less detergent, so are preferable where water is expensive or where the discharge goes into septic systems. However, these designs have a greater repair and failure rate than top-loading designs, and I found out why.

    I went into the garage to check it out. I noticed that the tub had fallen and the gasket had twisted, which indicated structural failure. First, Frigidaire uses screws with square holes in the heads, so I had to use my socket screwdriver with the right bit. I removed the panel and confirmed the tub had fallen. I then looked at the suspension system and found that one spring had failed. Further examination revealed that one of the damping struts had also failed. The machine was hosed. Being a Frigidaire and on a Sunday, I was not going to find the parts. Being an engineer :biggrin:, I saved the spring parts.

    My wife was thoroughly pissed because of the continuing problems with this machine, and she wanted a new dryer anyway, so we went to Sears to buy a new washer and dryer. The cost was $1500 with a 5 year service agreement on the washing machine, which it turns out is a Frigidaire built for Sears under the Kenmore label. Kenmore however has a better reputation, and at least, we can get servicing done faster and at lower cost.

    So we returned home and I tried to jerry-rig a support system - basically a brick wrapped in a towel under the tub frame in the rear, and a 4x4 in the front. Well that worked well until the final rinse. The final rinse is high speed (don't know the rpm's), and with an 'unbalanced' load, which is inherent in the front-load designs, the tub vibrates. Well, I had to hold down the washing machine while holding the 4x4 while the tub bounced up and down. No wonder the spring failed, it was subjected to periods of low-amplitude/high-amplitude cyclic loading - a recipe for failure at relatively low cumulative cycles.

    The problem could possibly be poor installation procedure in the factory, which leads to a vulnerability in a high stress/fatigue environment. In the upper hook, the spring failed at the middle of the 'C'. There appears to be a slight depression on the inside curve of the 'C', and at the top of this depression is the location of the initial site where a flaw propagated across the diameter of the spring (perpendicular to axis of spring wire). The fatigue pattern is classic from the flaw outward in a fan shape to about the central axis of the spring wire. From there the fracture surface is about 30° with respect to the spring wire axis in the center core of the spring, and 45° near the OD (as is expected in classic ductile shear failure). There is some bending indicated also. I hope to find a microscopic camera somewhere, preferably a Materials Science lab to get some closeups.

    I suspect the depression on the inside curve of the spring hook was made during installation, when the spring is stretched to put in place - a cross brace in the frame of the washing machine. While trying to hold down the washing machine and hold steady the tub during the high speed final rinse, I got a good feel for the high loading on the spring. The failure of the damping strut also contributed to problem.

    Second - As for the second product failure, I was using a pick with a 36" head to remove some tree stumps (when I was interrupted to deal with the failed washing machine). I was trying to pry up a root when the pick handle broke. The break occurred just below a plastic fitting on the head of the wood handle. The plastic fitting is fastened to the handle (probably by adhesive - I haven't opened the failed handle yet), and it provides an interface between the wood handle and metal tool head. The plastic handle provides an area which is somewhat impact resistant if the user misses the objective and accidentally hits the handle, it reduces the stress on the wood, and it reduces the wear from the metal tool head.

    However, I noticed that the wood handle was scored just below the plastic - possibly something that happens during manufacture or perhaps during shipment(?). When I bought a new handle ($11), I noticed a similar scoring pattern. This scoring pattern undermines the structural integrity of the handle. So I will see how long it lasts. The store clerk suggested that I keep the purchase receipt and if the handle breaks, I can return it and receive a free replacement ( :biggrin: ). I'll probably need one next year.
     
    Last edited: May 15, 2005
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  3. May 16, 2005 #2

    FredGarvin

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    Bummer about the washing machine. Not too much you can do about that one.

    The pick handle...you said it was scored? Was it scored around the entire perimeter, along the longitudinal axis of the handle, or is it one circumfrential score? It sounds like it may be knurling for the press fit if it is the former. Wood handle tools have always been my bane. I seem to go through at least one shovel handle a year.
     
  4. May 16, 2005 #3

    Astronuc

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    The washing machine is a lost cause. Too much of a headache.

    The scoring on the pick handle is circumferential. It is more like a scratch than a knurl. I will have to look closer at the old and new, but the scratched (scored) area, where the break occurred, did show some discoloration due to weathering.

    I tend to wear out shovel handles, too. :biggrin: I am looking into fiberglass handles.
     
    Last edited: May 16, 2005
  5. May 16, 2005 #4
    I went with a fiberglass/composite handled landscaping axe when it came to chopping at things. It's alot more forgiving if you hit the handle on something, also I think there's some shock absorbing effect for your arms if you hit something hard (like an unseen rock or a knot :yuck: ). I'm planning on switching over to as many composite handled yard tools as possible. I had an ice chopper, root chopper, edger for about a month when the wood handle snapped on me. I went at an angle chopping some roots on a bush I was removing, the head got jammed under the root bulb and when I went to lever it side to side to get it loose the thing just snapped off right in my hands (where the handle joins the head).Imagine my consternation at then having to dig my chopper head out from under the root bulb so I can replace the handle :rofl:
     
  6. May 20, 2005 #5

    russ_watters

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    I have an apartment, so not too many tools yet, but I love my graphite handled hammer. No wood for me.

    Random aside, but product failures are something that makes life interesting as an engineer. Anyone else just says 'hmmm broken - guess I have to get it fixed/replaced'. For an engineer, unless its under warranty, we have to rip it apart and see if we can fix it first.

    And personally, I'm extremely disappointed when I can't find/fix a problem. I recently had a mini-stereo system beat me, much to my dismay. The cd player stopped working and after taking it apart, I found a ribbon cable attached to the cd tray that was coming apart. It had a crease in it, so the flexing as the cd tray opened and closed concentrated at the crease and caused a fatigue failure. It wasn't easy, but I spliced it back together and I'm pretty sure I had it fixed (it checked out with a multi-meter), but the cd player still wouldn't work. Must be something else wrong and I can't figure out what.

    I may have posted this before, but a few years back I had a camera break and I won that one. The camera had one of the first two-step shutter releases and the mechanism wasn't very good - it required more force than it should have. Well, the button was on a small pcb on top that was cantilevered out from its framing, but supported by another pcb inside the front face of the camera. Well - supported by a series of soldered circuit traces to form the joint. And yep, you guessed it - fatigue again: pushing the shutter release flexed the solder joint, eventually making it fail. I sent a nice two-page engineer-ese letter to the company about their shoddy engineering and they fixed it for free (too small for me to solder it myself).
     
    Last edited: May 20, 2005
  7. May 20, 2005 #6

    FredGarvin

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    One of these days I'll learn and quit my cheap ways and buy fiberglass. I just need to get over the initial sticker shock.

    I am always disappointed when something does break and, after taking it apart, you come to find out it is not possible for you to troubleshoot. Usually it's an electronic component or a board. For example, right now I have a great Kenwood equalizer that the outputs have gone tits up on. I have looked through it, but nothing readily apparent is wrong. Grrrr.
     
  8. May 20, 2005 #7

    DaveC426913

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    Jehosephat! Does your wife get pissed when you burn up the afternoon in the lab instead of in the garden? :smile:

    I have an idea for a new show: CSI Engineer. Kind of like Michael Crichton's 'Airframe' (only better).

    That'd be cool!
     
  9. May 20, 2005 #8

    Astronuc

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    Yeah, kinda. :biggrin: She gets testy if I spend too much time on-line or doing research, rather than house/yard work. So I have to balance it all.

    So while I am gardening, landscaping, mowing, digging, repairing - I do a lot of thinking. :biggrin:

    Yeah, to engineers. :rofl:

    Ah! It's so great to be an engineer. :biggrin:
     
  10. May 20, 2005 #9

    FredGarvin

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    Discovery Channel occasionally has a show called "Failure Analysis" that goes through all of the investigation of a certain accident. They are for the layman so they do not go into much detail and tend to talk to you like you are in 5th grade, but they are interesting to watch.

    I wouldn't mind the same thing but with more in depth technical discussions and topics that don't include huge human tragedy.
     
  11. May 20, 2005 #10

    PerennialII

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    You guys subscribe to Elsevier's "Engineering Failure Analysis" ? A journal which is actually really fun to read, gives the in - depth along with the layman stuff. Nice kind of a semi-scientific journal, lighter read.
     
  12. May 20, 2005 #11

    Astronuc

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    I think we need - "The Engineering Channel". :rofl:

    I can just see it now - "Reality Engineering" or "Desparate Engineers" :rofl:

    and they say that Engineers don't have a sense of humor. :rofl:

    Perennial, thanks for the reminder about "Engineering Failure Analysis". I (and my company) do not subscribe, but I will look into it. I think I received a free trial issue when it was first published. I need to look into it again.
     
  13. May 21, 2005 #12

    FredGarvin

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    Desperate Engineers is usually redundant.

    I don't think I'd want to see any of those cast members in Playboy.

    That's what my wife keeps telling me!
     
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