Nonlinear Structural Solutions

Use-Case

Here a back face drop of the phone was considered when falling from height with a speed of 5 ms^-1.

How many times have you accidentally dropped your cell/mobile phone on the floor?

The most common failure mode of cell/mobile phones is the impact, due to an accidental drop. So, the manufacturers aim to develop products that are impact-resistant and can survive the drop test from a specific height where the cell/mobile phones are expected to continue functioning after suffering a drop with no or only minor damage. In general, phones are analyzed in a drop test using 12 load cases (Figure 1).

The FEA simulation will help designers understand how components interact in the assembly and how the failure mode and mechanism are developed under the impact loading. Understanding impact strength is an important consideration to ensure an adequate service life for such portable products. Multiple drops in sequence must be accounted for to ensure that the product continues to perform correctly and meets requirements for strength and safety. In general, phone manufacturing companies perform continuous or consecutive drop tests in which the handset is dropped several times on the ground to evaluate the durability, possible cracks on the phone and the functionality even after dropping the phone.

Figure 1. Analysis Orientations

FEA Model Description

A drop test analysis of the phone was conducted, considering various parts of the phone including buttons, camera, Printed Circuit Board (PCB), glass, touch-sensors, battery, etc. Nonlinear contact and nonlinear materials for these parts were assigned.

Fixed supports are applied to the ground and the phone was dropped. The scenario is solved using Explicit Analysis in OptiStruct in a time of 1 millisecond.

Figure 2. Back Face Drop Test

Results

Figure 3. Displacement Contour

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/Drop_test.fem

In this analysis, the phone is kept on two cylinders which are fixed as shown in and then force is applied on the phone in the middle. Tests are usually performed on both front and backside of the phone.

Use-Case

Cellular phones are generally made of aluminum for enabling a lightweight construction and for the ease of manufacturability. Phones have become increasingly slimmer and lightweight, reducing their structural properties. Metals commonly used in construction such as aluminium are flexible by nature and this exuberates the problem of bending.

When the phone is kept in the back pocket and someone who sits with the phone in the pocket, chances are high of the phone bending. This phenomenon of bending can be measured with a 3-point bending test, which is performed with the normal force that is generated when a person presses the back pocket is approximately 300N– 400N.

FEA Model Description

The phone is kept on two cylinders which are fixed (Figure 4) and then a force is applied in the middle of the phone. Lower two cylinders are fixed, enforced displacement of 8 mm is assigned to the pressing cylinder. Contacts between the rigid cylinders and phones are assigned.

Figure 4. FEA Model

Results

Figure 5. Displacement and Stress Contour Plot

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/3pt_Bending.fem

Use-Case

When a phone is laying on a table and a bunch of keys or a bag is dropped on the phone accidentally, what would happen to the phone? Either the screen will break or there will be some scratches on the phone. A ball impact test is performed to check for the hardness, scratch resistivity and the penetration resistance of the phone.

FEA Model Description

A phone is placed on a floor and a rigid ball is dropped on the surface of the phone with velocity of 2 ms^-1. The ground is constrained by fixed support and the problem is solved using Explicit Analysis, with a termination time of 1 millisecond.

Figure 6. FEA Model

Results

The ball impacts the phone with a velocity of 2 ms^-1. Displacement and stress contour plots of the phone screen and front cover are shown in Figure 7.

Figure 7. Stress Plot and Energy Plot

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/Ball_Impact.fem

Use-Case

The trend of larger screens, whether it be a laptop, computer, television or phone, is portable, as well as it folding into a 6 or 5.5-inch device. To ensure the durability of the phone throughout its life cycle, each part has to be checked for bendability – the glass, small batteries, and the screen are the main concerns, which should not break during folding.

Figure 8. Foldable Phone. Motorola Razr V4

FEA Model Description

This analysis of a foldable phone is different from the 3-point bending of the phone, as the lower cylinder is enforced to move vertically upwards in this analysis, unlike the fixed cylinders in the 3-point bending analysis.

Figure 9. FEA Model

Figure 10. Deformed Structure

Results

Figure 11. Displacement Results for Both Sides of the Folding Phone

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/Folding_Phone.fem

Use-Case

Washing machines are commonly used in almost every home worldwide. These appliances make it easy to clean clothes by going through the wash/agitation cycle, rinse cycle and spin cycle. The performance of these machines is based on the rotation of the clothes inside a drum, while they are mixed with water and cleaning powder or soap. It is natural that a load of clothes, when they are soaked in water, can create big reaction forces in the drum because of the weight when they are rotating. This situation makes it very important to calculate accurately the mechanical characteristics of the drum.

A lot of washing machine manufacturers conduct various tests for different applications of washing machines, such as water temperature, pressure applied, allowable size of the load, etc.

FEA Model Description

A rotational displacement is applied on the drum and a vertical load is applied to replicate the loads from the clothes and the rotation of the washing cycle. The lower part of the drum is fixed to the ground via spring elements which will allow the cylinder to move vertically. The rotational joint is assigned between the drum and the joint, so that the drum can rotate along the axis of rotation (Figure 12). Nonlinear Static Structural Analysis is performed to evaluate the strength of washing machine.

Figure 12. FEA Model

Results

Figure 13. Displacement Plot. side and top views

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/Washing_Machine.fem

Use-Case

Battery packs are a set of batteries arranged in a series or parallel, to provide the required power to electronic devices. The application of such battery packs is wide-ranging from phones to lawn mowers, automobiles to agricultural applications. The cells in the battery pack are the smallest energy resource entity that needs to satisfy a number of critical tests to fulfill the requirements for better characterization of battery cell components. Battery packs of an automobile can be bent because of accidents or overheating, which is very hazardous, as it can lead to a fire. The lithium-ion battery packs are not bendable or twistable, so repeated bending of such batteries can deteriorate the charging and discharging cycle, as well as the life of the battery.

FEA Model Description

A set of battery packs are modeled along with the cover. Frictional contacts are assigned between the cover and the batteries. A pressing cylinder allowed to press the battery pack with enforced displacement of 4 mm and the battery pack is rested on the fixed cylinder.

Figure 14. FEA Model

Results

Figure 15. Displacement and Stress Plots

Model File

<install_directory>/hwsolvers/demos/optistruct/examples/Battery_Pack.fem