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Filled Plastic Container Drop Simulation

Plastic Container Drop Simulation with Realistic loads

Plastic containers are common sight in day-to-day life. These containers typically come with manufacturer’s warranty of minimum 10 years. These outdoor containers experience harsh weather conditions in winter. Made of Polymer material, which are ductile in nature, their behavior are subject to change in extreme cold conditions to more hardened and brittle. With high warranty life, it is crucial for the manufacturers to consider different aspects such as operating conditions in terms of weather, abusive loads and usage while designing these containers. It is highly crucial for them to conduct physical drop tests on these containers under above conditions to be confident on its performance. Similar to any other engineered products these containers have to undergo multiple design changes and physical validations before being rolled out for production. The aim of this blog is to show case how finite element simulation can help in virtually drop testing these products under realistic loads and conditions. This can help manufacturers to come up with good designs in a short span of time reducing design cycle time, reducing physical prototyping and testing as well as be confident on product performance in the field.

Abaqus Unified FEA product suite from Dassault Systemes is an efficient tool for transient dynamic procedure that is required for drop simulations to generate more realistic loads. To demonstrate the capability we have used a simple outdoor trash container model with non-linear material properties and realistic loading to simulate the drop and the results are presented here.

The Finite Element Model

The scenario we are modeling here is that the container is dropped from a height of 12 feet with 90kg of load inside the container. The model of the container is meshed using shell elements. The container is considered to be made of Polymer material. The material properties taken here is a typical elastic-plastic material data tested at cold condition of -25oC. This would ensure that the model is tested under severe weather conditions.  The container is assumed to be dropped on a rigid floor.

The container is tested for two different conditions (two different analysis), one filled with water and the other one filled with soil. Both soil and water are modeled in eulerian domain to capture the behavior of the materials as well as transfer of loads to the container accurately. The coupled eulerian-lagrangian (CEL) capability available in Abaqus/Explicit is used for soil/water to container interaction. General contact in Abaqus/Explicit would ensure the interaction is captured and loads are transferred. The material model chosen for both soil and water is equation of state (EOS) model available in Abaqus and appropriate physical behavior of the materials is provided. Care has been given in choosing the viscosity and wave speed of both the materials. These are inputs required for EOS material model.

Shown below is the container assembly FEA model with wheels and rigid surface. The solid wheels are also made of Polymer material and are connected to the container using rigid beam connector. The second picture shows the eulerian mesh around the can.

container-euler

The container is assumed to free fall from a height of 12ft. To reduce the unnecessary computational time, the container is moved closer to the rigid floor and the accumulated velocity from the drop is calculated and given as initial velocity to the whole model. Further gravity load is also defined to the whole model. The floor is fixed.

Results

Shown below is the animation of deformation on the container filled with soil. The animation also shows the soil displacement on the right.

soil_can

The following animation is deformation of container filled with water with water displacement on the right.

water_can

It can be clearly noted here that both filler materials behave differently due to their density, viscosity etc. Because of this, there are differences in the way loads are transferred to the structure. It is important to simulate with right conditions and physical phenomena to capture the right behavior of the products tested. Abaqus with CEL technique is able to model interaction between fluid and structure accurately.

transparent4

The simulation can be used to find the potential crack initiation zones in the container with the zones having high plastic strains. It can be noted from the below pictures that the hotspots are different for soil and water. The picture to the left shows for soil, while water is on the right. Further, it is understandable that the container filled with soil having more hotspots compared to the one with water since soil is denser than water and consequently more load transferred to the container.

PEEQ

The following picture shows high strains at a location slightly lower for the soil than for water. This could be due to highly dense and viscous nature of the soil tending to stay low.

PEEQ_2

Conclusion

As a concluding remark, Abaqus unified FEA product suite can be effectively used to simulate the drop test of the container with realistic loads eg. Soil, Water etc. This simulation can give deep insight into the behavior of the container with potential hotspots for crack initiation, allowing the engineers to make necessary design changes for a safer design without going through the tedious and time consuming physical tests.  This drop simulation could be part of a routine design process to optimize the geometry before manufacturing the (expensive) mold.  It is also possible to simulate successive drops to evaluate the cumulative damage of numerous events.

Finally, additional capabilities of Abaqus such as Discrete Element Method (DEM) can also be used to simulate the drop test of a container in cases were solids parts such as wooden pieces or rocks are to be considered in the container.

References

  1. Coupled Fluid / Structure Interaction Simulation Using Abaqus CEL, GM Fuel CAE, SIMULIA Community Conference, May 2010
  2. Section: 2.3.2 Impact of a water-filled bottle, Abaqus Example Problems Manual, Abaqus Documentation 6.14
  3. Section: 14.1.1 Eulerian analysis, Abaqus Analysis User’s Manual, Abaqus Documentation 6.14