Calculating Young's modulus from an experiment - values are all inaccurate? Watch

username2638907
Badges: 13
Rep:
?
#1
Report Thread starter 1 year ago
#1
As part of a practical experiment I used a tensometer to record the fracture force of several materials (steel, aluminium, polypropylene)

I measured the thickness, width, and length of each sample before testing it and used this to calculate the area. From this I calculated the stress and I also calculated strain by measuring the new "length" after fracture and by doing extension/length.

However, now that I have calculated a value for Young's modulus for each material, I notice that they're all rather inaccurate. For example, for steel I got a value of something like 1.3x10^9, however the value for steel is apparently usually 2x10^11 (according to https://www.engineeringtoolbox.com/y...nsile_strength)

Is this because Young's modulus is only linear up to a certain point (limit of proportionality), and I got inaccurate values because I'm measuring at the fracture point? If so is there a way around this?

Thanks!
0
reply
uponthyhorse
Badges: 15
Rep:
?
#2
Report 1 year ago
#2
I believe you're correct, The stress-strain curve for mild steel is shown below, if you're measuring the extension at the fracture point then you're essentially treating the curve as a straight line from the origin to point of fracture, which has a lower gradient than the straight line portion of the curve, hence lower Young's modulus value. Presumably you can work around this by recording the length at discrete load values?
Name:  450px-Stress_Strain_Ductile_Material.jpg
Views: 81
Size:  16.2 KB
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Birmingham
    Postgraduate Open Day Postgraduate
    Wed, 20 Mar '19
  • King's College London
    Postgraduate Taught Courses - Arts & Sciences - Strand Campus Postgraduate
    Wed, 20 Mar '19
  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 20 Mar '19

Where do you need more help?

Which Uni should I go to? (36)
13.95%
How successful will I become if I take my planned subjects? (21)
8.14%
How happy will I be if I take this career? (54)
20.93%
How do I achieve my dream Uni placement? (37)
14.34%
What should I study to achieve my dream career? (32)
12.4%
How can I be the best version of myself? (78)
30.23%

Watched Threads

View All
Latest
My Feed