ASR has a strong history conducting many analyses representing aerospace fuel tank qualification drops.
The video in Figure 1-1 depicts a composite fuel tank drop test simulated using LS-Dyna. While a real life drop test is required for tank qualification in all applications, the explicit solver of LS Dyna has proven to be a critical component in identifying problematic areas within fuel tanks prior to any necessary drop tests. This foresight helps to reduce the total number of drop tests conducted to achieve a qualifying product, and thus saves clients the time, effort, and resources typically associated with conducting numerous tests.
The main reason LS Dyna simulations have had such high success is the flexibility to cater each individual model to match the client’s expectations and requirements. Model flexibility includes specific inputs and outputs such as composite ply lay-up order, fiber directions, X% full fuel tanks, or ply specific stresses and strains on a time-history level. Figure 1-2 depicts the ply-specific stresses over time of a 2-ply fuel tank during a drop test.
The capability of analyzing model outputs on a time-based level is a key component of predicting when and where product failure can occur. Other important results to analyze include composite to metal fitting bonds, fluid-structure interactions such as pressure, and predicting individual ply failure.
An accurate dynamic analysis has not only helped various clients meet qualification requirements, but has also served as a cost effective research and development tool. Many times a company will shy away from implementing historically “out of the box” ideas in tests due to overall resource and time constraints as well as the uncertainty of performance. Proposed ideas can be implemented into the pre-existing dynamic models and analyses can be conducted to investigate the benefits or detriments without the typical setback associated with developing a new test from the ground up. Multiple boundary conditions can be tested as well; such as various angles of impact, drop height, or amount of fuel within the fuel tank. Figure 1-3 shows the same tank dropped from two different orientations, one parallel to the ground and the other with one tank end biased toward the ground. Analyzing various boundary conditions ensures that the product goes above and beyond, and satisfies more than the base qualifying requirements.