Tensile test analysis

Tensile test analysis#

General scope#

From global point of view, test machines, sensors provide time-stamped data. Most of the time this a data are stored in a tabular shape, i.e. one line for each record with its time-stamp.

A common way to store this data is to use ‘.csv’ file. A ‘.cvs’ file looks like:

time;data1;data2;data3
0.0;12.;.001;'blue'
0.1;11.5;.002;'red'
0.2;14.2;.004;'blue'
0.3;14.2;-.004;'green'
...
...
...

The Pandas module is a convenient way to manage this file (read and write).

In addition, metadata can be stored in this file, at the beginning of the file. In this metadata global info can be stored, as the date of the test, the name of the operator, the material, the sample type, commentary…

A total file can look like:

date : 01-02-1900
user : bob
material : Steel 
length : .5
remarks : This test is awsome

time;data1;data2;data3
0.0;12.;.001;'blue'
0.1;11.5;.002;'red'
0.2;14.2;.004;'blue'
0.3;14.2;-.004;'green'
...
...
...

Session objective#

In this session you are asked to analyze data coming from the tensile test. This analysis aims at extracting the mechanical properties of the material, such as the Young modulus, mechanical strength and yield strength from the load/displacement curve.

At the end of this session, you should have a class that is able to deal with the data coming from a tensile test.

The dataset :#

Required files

It can be downloaded at this link TensileData.

It contains 4 files, the unit are s/N/mm :

Test_1.csv
Test_2.csv
Test_3.csv
Test_4.csv

# Setup
%matplotlib notebook
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib as mpl

Q1 : Load the data and plot its#

code one function that loads one test
call this function 4 times to load all data
plot all the tests on one figure

Q2: Load the metadata#

Into the ‘.csv’ file the first 2 line provides \(S_0\) and \(l_0\) of each sample.

code a function that read this data
call this function on each test

Useful function#

Tip: split a string into 2 parts

line = "z = 143.2"
word1, word2 = line.split("=")

Q3: Stress/Strain curve#

Knowing that: \( \sigma_n = \frac{F}{S0} \) and \( \epsilon_n = \frac{\Delta L}{L_0} \):

Code a function that computes the strain and stress data.
Apply the function to all tests.
Plot this data for all test on a graph.

Q4: Mechanilca strength#

Code a function that computes the mechanical strength.
Apply the function to all tests.
Plot this data for all test on a graph.

Q5: Young modulus measurements#

Code a function that computes the young modulus on each test.
Apply the function to all tests.
Propose a plot to illustrate the young modulus measurements

def get_young_modulus(df):
    E = 0.0
    return E

Q6: all together in a class#

Include all the function you have coded in a class.

Below is a simple template of the class that you should build :

class TensileTest:
    """
    this class is able to ....
    """

    def __init__(self, csv_file="xxx"):
        self.csv_file = csv_file
        # CODDE HERE

    def __repr__(self):
        return "<tensileTest: (file: {0}, E = {1:.2} MPa)>".format(
            self.csv_file, self.get_YoungModulus()
        )

    def get_meca_strength(self):
        return 0.0

    def get_YoungModulus(self):
        # CODDE HERE
        return 1.0

test1 = TensileTest("my_csv.csv")  # call the __init__ function

test1  # call the __repr__ function

<tensileTest: (file: my_csv.csv, E = 1.0 MPa)>

Q7: The plastic side of the force#

compute the plastique strain (\(\varepsilon_p = \varepsilon - \dfrac{\sigma}{E} \))
fit the stress / plastic strain curve with a power plastic law (\(\sigma = \sigma_0 + K {\varepsilon_p}^n \))