Design For Longevity

Every Engineer and Designer wants two things from their designs.  The design needs to work as expected, and the design needs to last.  The majority of the designs are designed for longevity. However sometimes due to an oversight in the design stage recalls and under warranty repair costs skyrocket.  SOLIDWORKS Simulation Standard addresses these specific issues allowing design teams to catch issues early in the design cycle.

As an example let us discuss a cast alloy steel handle (35,000 psi yield strength) subjected to a 500 pound pull load.  The handle is fixed about the two bolt locations top and bottom.

The ultimate design constraints is that the handle withstand the 500 lb load keeping the Maximum Von-Mises below 18,000 psi, and a Factor of Safety(FOS) of 2.0 or higher.  The design also needs to last 50,000 loading cycles exceeding the demand calculated based on average use.

To start the handle needs to be tested for a constant loading of 500 lb to ensure the initial design using 1 mm thick internal ribs meets our criteria above.

The design does not pass showing a stress of 29,000 psi and a Factor of Safety of 1.17(35,000 psi/29,000).  

A second design change to meet the FOS of 2.0 or higher is implemented increasing the thickness of the ribs to 2 mm.

The Stress reported to be 17,380 psi and a FOS of 2.01.  The results are within the design specifications however we want to test a third option to verify the design cannot improve by thickening the ribs again.

The ribs were then thickened to 3 mm for a third design iteration.

The 3 mm version showed a stress of 16,952 psi and a FOS of 2.06.  This is a marginal benefit above iteration 2, based on the amount of weight and material now added.

Quickly and easily we were able to test the design virtually meeting all of criteria.  This saved time and money reducing the number of physical prototypes.  Now that design iteration 2 meets two of our three design goals.  The third goal is to verify the design can handle at least 50,000 cycles of the 500 lb load being applied.  To do this we turn to the Fatigue Analysis portion of Simulation standard.

The existing 500 lb load study will be used as it will be the baseline for the fatigue study.  After selecting a new fatigue study the user only needs to provide two things.  The loading condition.  In this case the load of 500 lbs will be fully reversed and applied 50,000 times.

The second needed specification is the Stress to Number of cycles curve.  This curve can be found empirically or in ATLAS of Fatigue Curves, and other publications.

The fatigue analysis has an output of Life Expectancy, and Percent Damage.  The part showed 71% at the areas of high stress, and a maximum life of 69,789 cycles.

Fatigue analysis is best utilized for multiple loading cases and combinations giving invaluable insight into the design.  Fatigue gives the user an understanding of the design longevity helping eliminate rework and warranty claims.  Do not hesitate to reach out to 3DVision Technologies if you have any questions or would like to know more about how Simulation standard can help you design better, faster, and smarter.