# Constructing SN Curve from Data

• geffman1
In summary, the speaker is asking for help in creating a SN curve for their data on Excel. They mention struggling with getting a curvy straight line and offer to email the data to anyone who can help. They also clarify that the project is not very in-depth as it is a first year project.

## Homework Statement

hey guys i have to make a SN curve for this data (on excel), however when i do it i always get a curvy straight line? if anyone would like to help i can email them the data, its a first yr project so isn't to indepth.
thankyou

geffman1 said:

## Homework Statement

hey guys i have to make a SN curve for this data (on excel), however when i do it i always get a curvy straight line? if anyone would like to help i can email them the data, its a first yr project so isn't to indepth.
thankyou

You don't say anything much about your data... But time curve data often looks like a series of pairs. If so, make sure you use the X-Y chart styles in Excel.

geffman1 said:
curvy straight line?

## 1. What is an SN Curve?

An SN Curve, also known as a Wöhler curve, is a graphical representation of the relationship between the applied stress and the number of cycles to failure for a specific material.

## 2. How is an SN Curve constructed from data?

To construct an SN Curve, data points are collected by subjecting a material to various levels of cyclic stress until it fails. The applied stress is plotted on the x-axis and the number of cycles to failure is plotted on the y-axis. A smooth curve is then fitted through the data points to represent the trend of the material's fatigue strength.

## 3. What factors can affect the construction of an SN Curve?

The construction of an SN Curve can be affected by various factors, such as the type of loading (tension, compression, bending), the geometry of the sample, the surface finish, and the environmental conditions (temperature, humidity, corrosive agents).

## 4. How is an SN Curve used in engineering?

SN Curves are commonly used in engineering to determine the safe operating limits of a material under cyclic loading. By comparing the applied stress to the SN Curve, engineers can estimate the number of cycles the material can withstand before failure. This information is crucial in designing reliable and durable structures and components.

## 5. Are there any limitations to using an SN Curve?

While SN Curves are a useful tool in predicting fatigue life, they have some limitations. The data used to construct an SN Curve is typically obtained from laboratory tests and may not accurately reflect the real-world conditions. Additionally, the curve may not account for variations in material properties or manufacturing processes. Therefore, it is important to use the SN Curve as a guide and not rely solely on its predictions.