Chapter 1, lesson 1 Flashcards
(14 cards)
What test samples are use for tensile test?
Dog bone tensile test samples
1. Rectangular plate
2. Circular bar
What is a unique trait of the samples?
•The two ends of the sample are wider in width and have a bigger diameter
•It is being mounted on a testing apparatus
How to calculate the gauge length of the test sample?
Gauge length= 5.65 √ area
What is the special trait of the central region of the test sample?
• It’s the uniform cross section
• It is narrower compared to the ends
• Only central region can stretch during testing
How does the tensile test actually conduct?
• A pulling force known as Tensile force
• The tensile force is applied at the opposite of the two fixed end of the sample
• The force will only increase until the sample breaks
• This force is measured by a cell load
What are the 4 stages that happen in tensile test
Stage 1: Elastic Deformation
Stage 2: Plastic Deformation
Stage 3: Necking
Stage 4: Breaking
What are the 3 features in the Force extension curve?
- Elastic Limit that happens right after elastic deformation
- yield point happens during plastic deformation
- Maximum point happens before Necking
What can we derive from the Force-Extension curve?
- Tensile strength (UTS), the highest stress applied without any fracture, the ability of the material to resist the application of tensile force without rapture.
UTS= MAXIMUM FORCE/ORIGINAL CROSS SECTIONAL AREA
- Yield Stress, is the stress required to start deformation and measure the resistance to deformation
YIELD STRESS = FORCE AT YIELD POINT/ORIGINAL CROSS SECTIONAL AREA
How do we find the ductility of a material?
By the Elongation percentage and Areas Reduction.
%E = final length -original length/ original length ×100%
%A = final area- original area/ original area ×100%
The higher the %A/%E, the more ductile the area
How to measure stress when there is no yield point?
Using Proof Stress, which is the stress required to start with a specified amount of permanent extension.
1: Find gauge length first
2: calculate specific extension percentage
3: find intersection point, by drawing a parallel line up
3: stress = Force/ original area
How to find the strain?
Strain= extension/original gauge length
Describe the stress-strain curve
The steeper the gradient, the little the deformation. Which means modulus is little and the material is flexible
The gentler the gradient , the more the deformation. Which means modulus is more and the material is ductile
How to calculate young modulus?
• Young modulus is to measure the stiffness of the component
•Young modulus= stress/strain
What is the relationship between strength, hardness and ductility
The higher the strength, the higher the hardness but lower the ductility
