Until roughly 60 years ago, introducing a new product or design change was based largely on paper drawings and an extended series of physical prototypes. This build-it, break-it process was time consuming, costly, and did not easily lend itself to innovation.
Today products are represented with CAD models and their performance is checked by recreating real-world conditions virtually. The process is known as engineering analysis or simulation and is supported by a long list of sophisticated software applications (such as Nastran, Ansys, LS-DYNA, Etc.).
These applications allow analysts to input loads and calculate the stresses and strains to validate the structural integrity of that design. Because it’s important that these inputs mirror conditions consistent with the real-world operation of the product, the inputs must be rooted in the physics. Baseline data points are often obtained by monitoring similar products in use. The inputs typically simulate the normal operation of the product along with extreme conditions in seismic, military, marine, and off-road applications Analysis also provides guidance for validating the final product and helping locate strain gages in areas of potential concern.
Inputting accurate loads is paramount. And there are software applications that ensure that this is the case. One such program is True-Load from Six D partner, Wolf Star Technologies.
The software guides the laying of strain gauges on equipment in critical locations that can be used to back calculate operating loads. This data is used to calculate the operating loads on the structure. From this, automatic strain correlation reports are generated showing cross plots of simulated strain plotted against measured strain. Users typically see strain correlation between 5% and 2% on their FEA models using the loads calculated by the program.
Wolf Star’s President & Founder, Dr. Tim Hunter explains the process. “The technique begins with the engineer setting up unit loads on an FEA model. The software analyzes these results and suggests optimal strain gauge placement. A correlation matrix relating strain response to the unit loads is stored to disk. The analyst works with the test engineer to lay the gauges at the indicated locations.
“Once the strains are measured in the lab, proving ground or field, the loads are calculated by multiplying the strains times the correlation matrix. This provides strain correlated loading the analyst can use to query responses anywhere on the structure and even generate operating deflection shapes. In addition, these loads are ideal for performing FEA based durability analysis.”
Capturing accurate data removes the guess work from analysis. Users typically eliminate one or more design-build-test cycles from the product development process. This saves hundreds of thousands of dollars and accelerates time to market.