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Liquid Storage Bag Fill Analysis

FEA Consulting

High-strength polymer bags are being used more and more as a low-cost solution for storing and transporting liquids. A major challenge is to develop bags that can store larger quantities of liquids without rupturing.  However, large bags filled with fluids can have high stress concentrations and unwanted fold patterns, and these stresses and folds can change depending on how the bag is oriented. Bag designers have found that they can change the stress concentrations and fold patterns by adding different seam patterns.  But, this can be a painstaking trial-and-error process where seam patterns are added, bags are manufactured, and folds and distress patterns are evaluated for each proposed design. A more efficient method was needed to rapidly evaluate the effects of different seam patterns.

CAE Associates determined that finite element models could be developed to do this quickly and efficiently. FEA models of seamed polymer bags were developed with the ANSYS Workbench/LS-Dyna software that simulated the process of filling the bags with a liquid in a specific orientation. This software was selected because it is best-suited to solving and predicting the highly nonlinear behavior associated with the motion of flexible membranes and fabrics. A worst-case condition showing a seamed bag in a vertical orientation and subjected to the maximum fluid pressure is shown in Figure 1 above. Predicted fold patterns and deformed shapes compared well with the patterns and shapes seen in actual bag designs for the same constraints and orientations.

 

These models are now available to the designers to help them make rupture-resistant liquid-storage bags in a variety of sizes and seam patterns. The models can be used to rapidly assess the effects that changes to the size and seam patterns have on the potential for rupture and undesirable folding. This ability offers the potential to significantly reduce the time-to-market whenever the need for a new bag design arises.