# Stress at c'sink holes of enclosed box with internal pressure

• patrickv
In summary, a customer is requesting that the battery pack chassis be proven to not burst or deform if additional gases are introduced inside. The chassis is assumed to be a sealed .05" thick 5052 AL enclosure with four countersunk screws securing a PC board inside. The volume of air in the box is 205.8 mL and the pressure inside and outside during installation is 11.777 psi. To find the pressure exerted on the inside walls, the ideal gas law can be used if the total mass of gas is known. To address any stress concentration around the countersunk holes, Roark's book can be consulted or they can be treated as circular holes under plane stress, taking into account the additional stresses from the screw/
patrickv
I have an issue I'm not quite sure how to approach. A customer is requesting that we prove that our battery pack chassis will not burst or deform if additional gases are introduced inside the enclosed box (the batteries could vent).

The chassis is assumed to be a sealed .05" thick 5052 AL enclosure with dims shown (attached). There are four countersunk screws attached to standoffs securing a PC board inside. The volume of air in the box is approximately 205.8 mL. If 2400 mL is introduced, how would I find the pressure exerted on the inside walls of the box and, more importantly how do I illustrate that the thinnest portion of the wall (at the countersinks) won't give. Pressure inside and outside the box during installation is 11.777 psi. Thank you.

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Couldn't you use the ideal gas law to calculate the pressure? You will need to know the total mass of gas inside your container. As far as the stress concentration around your countersunk holes, I would look through Roark's book to see if anything is listed. As a rough first approximation, you could treat them as circular holes under plane stress. Keep in mind that there will be additional stresses due to the screw/standoff and weight of the board.

## 1. What causes stress at sink holes of enclosed box with internal pressure?

The stress at sink holes of enclosed box with internal pressure is caused by the combination of internal pressure pushing outwards and the structural integrity of the box trying to maintain its shape. This creates tension and stress at the weakest point, which is typically the sink holes.

## 2. How does stress at sink holes affect the overall strength of the enclosed box?

The stress at sink holes can significantly weaken the overall strength of the enclosed box. If the stress is not properly managed, it can lead to cracks, leaks, or even structural failure of the box.

## 3. What factors contribute to the amount of stress at sink holes?

Several factors can contribute to the amount of stress at sink holes, including the size and shape of the box, the material it is made of, and the amount of internal pressure. Additionally, any external forces or impacts on the box can also increase the stress at the sink holes.

## 4. How can the stress at sink holes be minimized or managed?

To minimize or manage the stress at sink holes, it is important to ensure that the box is made of a strong and durable material that can withstand the internal pressure. Additionally, reinforcing the sink holes or adding support structures can help distribute the stress more evenly and prevent structural failure.

## 5. Is it possible to eliminate stress at sink holes completely?

While it may not be possible to completely eliminate stress at sink holes, it can be reduced to a safe and manageable level through proper design, material selection, and reinforcement. It is important to regularly monitor and maintain the box to prevent any excessive stress buildup that could lead to failure.