# Self teaching basic average shear stress calculation

• Koth
In summary, the conversation discusses the use of basic hand calculations and safety factors to reduce the risk of parts failing in a motorcycle project. The formula for calculating average stress and the use of shear strength in the safety factor calculation are mentioned. The individual is seeking advice and clarification on which values to use from the material datasheet for the specific scenario. They also mention the possibility of needing a more complex analysis and express their appreciation for any general advice.
Koth
Hello All

I am designing some very basic components for a motorcycle project at home, and because I am interested, thought I'd use it as an opportunity to refresh my memory in order to reduce the risk of the parts failing. To begin, I want to do some basic hand calcs if possible so have identified the very basic formula for calculation of average stress ( = F/A). Furthermore, I need to use a basic safety factor calculation to determine if the specified material will fail so have identified fs = Ys/Ds (Ys = material strength, Ds = shear stress).

I am concerned about a protruding piece of material that is subject to a load that will tend to shear the protrusion from the main body of the component (I will come back with a sketch if necessary). The load is applied perpendicular to the shear plane. Cross section area of the shear plane is 10.6 mm². Load is 400N.

Using the above formula I have ended up with a shear stress of 37.74 MPa.

Naturally, I have a few questions and would be extremely grateful if somebody could give some advice please?

Q1) Is this basic formula acceptable for this scenario?
Q2) When inserting values into the safety factor formula the material datasheet (6061-T6 alloy) offers Ultimate Tensile Strength, Yield Tensile Strength and Shear Strength. I have tried to determine which to use on the basis that I do not want the lug to deform beyond it's Yield point but I'm confused. Is the Shear Strength listed on the DS Ultimate or Yield? Or should I use the rule of thumb that I have found based on a calculated value of 0.577*Yield Tensile Strength? I have also seen a rule of thumb advising 0.6*UTS but assume this is for failure beyond the materials elastic limit?

I understand that a more complex analysis may be required so thank you in advance for your patience with this. As I said, any general advice much appreciated.

Koth

EDIT -- Sorry @Koth for liability reasons we cannot help you with this project. Please seek out a good local Mentor near you who can help guide you safely through this project.

Last edited:

## 1. What is shear stress?

Shear stress is the force per unit area that acts parallel to a surface, causing it to deform or slide. In simpler terms, it is the stress that occurs when two surfaces slide against each other.

## 2. Why is it important to calculate average shear stress?

Average shear stress is an important factor in many engineering and scientific applications, such as determining the strength and stability of structures and materials. It can also help in predicting the behavior of fluids and solids under different conditions.

## 3. How do you calculate average shear stress?

The formula for calculating average shear stress is τ = F/A, where τ is the shear stress, F is the applied force, and A is the cross-sectional area of the object experiencing the shear force. The resulting unit for shear stress is typically in pounds per square inch (psi) or newtons per square meter (N/m²).

## 4. What are some common examples of shear stress?

Shear stress can occur in various situations, such as when a wrench is used to tighten a bolt, when a river flows against its banks, or when a car turns around a curve. It is also an important factor in the design and construction of buildings, bridges, and other structures.

## 5. How can one improve their understanding of shear stress calculations?

Practicing with different examples, working through problems, and seeking guidance from a mentor or instructor are all helpful ways to improve understanding of shear stress calculations. Additionally, familiarizing oneself with the properties of different materials and the effects of different forces can also aid in understanding shear stress.

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