# Calculating Stresses at an Angle: Why Does it Matter?

• fonseh
In summary, the conversation discusses the use of an equation to determine normal and shear stress, specifically in a question involving stress on a plane. The question references an angle of 30 degrees and a method demonstrated in a link. The attempt at a solution involves calculations and references to an answer provided, which differs from the calculated result. The questioner is unsure if their concept is correct and seeks clarification.
fonseh

## Homework Statement

Why can't i use the equation to determine the normal stress and shear stress ? Is my concept wrong ? I use the method in the link to do this question. The question said the
stress on a plane making angle 30 degree anticlockwise from plane AD .

## The Attempt at a Solution

When it's anticlockwise , the angle is positive
http://www.dummies.com/education/science/using-mohrs-circle-to-find-principal-stresses-and-angles/
Mod note: Image of work has been deleted. OP will be including work in a subsequent post.[/B]

Last edited by a moderator:
$$\sigma _(max)$$ = ((25-15 )/2 ) + 20cos60 + 20sin60 = 32.3MPa$$\sigma x_(min)$$ = ((25-15 )/2 ) - 20cos60 - 20sin60 = -22.3MPa

But the ans is 12.5 and -2.3MPa

##r = sqrt ( ((\sigma _x -s \sigma_y) /2 )^2)+ (\tau_xy)^2) = 28##

##tan2\theta_p = 2\tau_xy / (\sigma _x -s \sigma_y)
= 2(20) / 40## , ##\theta_p = 22.5## degree ,
This is different from the ##\theta_p ## = -68 degree given

Last edited by a moderator:
Image for mohr's circle
https://www.physicsforums.com/attachments/dsc_0038-jpg.110448/

Is the ans provided wrong ? Or is my concept wrong ?

bump

## 1. What is the importance of calculating stresses at an angle?

Calculating stresses at an angle is important because it allows us to accurately determine the amount of stress applied to a material in a specific direction. This information is crucial for designing structures and materials that can withstand these stresses and prevent potential failures.

## 2. How is the angle of applied stress determined?

The angle of applied stress is typically determined through a combination of theoretical calculations and experimental testing. The material properties, loading conditions, and geometry of the structure all play a role in determining the angle of stress.

## 3. Can calculating stresses at an angle improve the durability of materials?

Yes, calculating stresses at an angle can help improve the durability of materials by allowing us to identify potential weak points and strengthen them accordingly. By understanding the direction and magnitude of stress, we can design materials that are better able to withstand these forces.

## 4. What are some common methods used for calculating stresses at an angle?

Some common methods for calculating stresses at an angle include the Mohr's circle method, the stress transformation equations, and the principal stress method. These methods use mathematical equations to determine the stress components and their directions.

## 5. How do engineers and scientists use the information from calculating stresses at an angle?

The information obtained from calculating stresses at an angle is used by engineers and scientists to design and analyze structures and materials. It helps them understand how different materials will behave under various loading conditions and how to optimize their design for maximum strength and durability.

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