In the analysis of aircraft and aerospace structures, several critical factors come into play. Safety is paramount, modifications must comply with regulatory requirements, and airplane manufacturers want changes done in a cost-effective way. Recently, avionics engineering firm Aquila Engineering in Australia found itself saddled with FEA software that was no longer supported. In its search for a new program, the company needed software that could import legacy models and offer an intuitive interface so engineers using other FEA programs could quickly learn the new software. Also needed was good product-specific training and ready access to knowledgeable support technicians.
According to Aquila, the software gave the company good compatibility between FEA and CAD and met the company’s technical needs. Femap with NX Nastran lets users import geometry directly from NX CAD to generate, in this case, FE models for analyzing aircraft structures.
A splice repair design for the upper longeron on a particular aircraft was underway when Aquila purchased the software. FE analysis was needed to predict the loads in all the members as well as generate rivet loads from the free-body diagrams for each part. Because the longeron undergoes a direct load, fatigue and crack-growth analyses were necessary.
Aquila used a refined version of an existing finite-element model to build the FE model of the longeron. The company compared FEA results with physical test data. “Using Femap with NX Nastran let us validate the model using measured strain data from a full-scale load test conducted years earlier,” says Aquila Engineering Manager Ben Terrell.
According to Terrell, the software has improved the company’s finite-element-modeling methods. He credits the software’s large variety of specific preanalysis tools for model definition, as well as postanalysis tools for results. “And the software makes it easy to sift through large amounts of engineering-results data with minimal effort and computer resources,” he says.
“The software has boosted our modeling and processing speeds by 50%,” says Terrell. “Also, NX
Nastran is a faster solver than we were previously using. Analyses are speedier due to NX Nastran’s capability to exploit a multicore processor.”
Terrell estimates that the software’s increased speed and accuracy has cut design costs by tens of thousands of dollars since its purchase. “We now have more confidence when tackling difficult problems and this attitude comes across in our interactions with customers. Using Femap with NX Nastran has directly improved the quality of our work, as evidenced by a downturn in the need for prototyping and testing. The software also helps us meet strict aircraft regulations,” he says.