Tensile Properties of Metals and Alloys
Jesse Columbus
Larry Lake
Steve Lish
IE 3122 Material Processing Lab
Section (Tuesday, 1p.m.)
Lab Group #6
This paper was submitted on this day,____________, for consideration in partial fulfillment of
IE 3122
__________________________,_________________________,_________________________
3.
The difference between engineering stress and true stress comes down to which cross
sectional area is used. With engineering stress the initial cross sectional area is used throughout
the stress strain curve, all stresses are computed using the initial area. True stress uses the
instantaneous cross sectional area of the material in tension. The area of the cross section is
always changing up until fracture. The difference in the graphs and tables is that engineering
stress tapers off after the Ultimate Tensile Strength (UTS) and curves down till fracture. With the
true stress strain graph the stress continues to rise up past the UTS until fracture. The stress is
higher for true stress because the stress is concentrated at the necked cross sectional area as the
cross section gets smaller the stress increases.
𝑇𝑟𝑢𝑒 𝑠𝑡𝑟𝑒𝑠𝑠 =
𝜎𝑎𝑡 𝑓𝑟𝑎𝑐𝑡𝑢𝑟𝑒
𝜎𝑓𝑟𝑎𝑐
=𝐴
𝑖𝑛𝑠𝑡𝑎𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠 𝑎𝑟𝑒𝑎
𝐸𝑛𝑔𝑖𝑛𝑒𝑒𝑟 𝑠𝑡𝑟𝑒𝑠𝑠 =
𝑖𝑛𝑠𝑡𝑎𝑛𝑡
𝜎𝑎𝑡 𝑓𝑟𝑎𝑐𝑡𝑢𝑟𝑒
𝑖𝑛𝑡𝑖𝑎𝑙 𝑎𝑟𝑒𝑎
𝜎
= 𝑎 𝑓𝑟𝑎𝑐
𝑖𝑛𝑡𝑖𝑎𝑙
𝐴𝑟𝑒𝑎𝑖𝑛𝑠𝑡𝑎𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠 =
𝐴𝑟𝑒𝑎𝑖𝑛𝑡𝑖𝑎𝑙 =
𝜋𝑑𝑓𝑖𝑛𝑎𝑙 2
4
𝜋𝑑𝑖𝑛𝑡𝑖𝑎𝑙 2
4
Aluminum
Brass
Steel
𝜋(.250")2
4
𝜋(.249")2
4
𝜋(.255")2
4
.04909𝑖𝑛2
.04869𝑖𝑛2
.05107𝑖𝑛2
𝜋(.162")2
4
𝜋(.147")2
4
𝜋(.162")2
4
. 02061 𝑖𝑛2
. 01697 𝑖𝑛2
. 02061 𝑖𝑛2
Force fracture
1,673 𝑙𝑏𝑠
1,939 𝑙𝑏𝑠
2,912 𝑙𝑏𝑠
𝑆𝑡𝑟𝑒𝑠𝑠𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟
1673𝑙𝑏𝑠
. 04909𝑖𝑛2
1939𝑙𝑏𝑠
. 04869𝑖𝑛2
2912𝑙𝑏𝑠
. 05107𝑖𝑛2
34,080 𝑝𝑠𝑖
39,823 𝑝𝑠𝑖
57,019 𝑝𝑠𝑖
1673𝑙𝑏𝑠
. 02061𝑖𝑛2
1939𝑙𝑏𝑠
. 01697𝑖𝑛2
2912𝑙𝑏𝑠
. 02061𝑖𝑛2
81,174 𝑝𝑠𝑖
114,260 𝑝𝑠𝑖
141,290 𝑝𝑠𝑖
𝐴𝑟𝑒𝑎 𝑖𝑛𝑡𝑖𝑎𝑙
𝐴𝑟𝑒𝑎 𝑓𝑖𝑛𝑎𝑙
𝑆𝑡𝑟𝑒𝑠𝑠 𝑡𝑟𝑢𝑒
8.
From the start of plastic deformation till the point of the UTS engineering stress
increases. The reason why the stress increases up to the point of UTS is because the material is
plastically deforming in a uniform fashion. The material in tension starts to work harden from the
strain of plastic deformation increasing the stress needed to strain the part. The stress increases
up until the UTS where necking forms causing the engineering stress of the part goes down until
fracture.
9.
In the later stage of plastic deformation, engineering stress decreases on the graph. This
deceiving concept in which stress seems to diminish, happens because of necking. All of the
stress concentrates at the necked region of the material. As the area decrease the stress actually
increases in a true stress strain curve. Engineering stress does not use the instantaneous area of
the necked region; it uses the initial cross sectional area of the material that is put in tension,
therefore creating the appearance that the stress is decreasing when in fact it is actually
increasing.
10.
The carbon content of steel can greatly effects how the steel will perform and it is
necessary for the producer to be aware of how it can affect strength resilience and toughness.
Increasing the carbon content of steel can greatly increase the strength of steel by increasing the
stress needed to deform the steel. Lowering the carbon content can lower the strength of it as
well as increasing the ductility.
Resilience and toughness go hand in hand; resilience is the area lying underneath the
𝜖
elastic deformation area up to the point of the yield strength. 𝑈𝑟 = ∫0 𝑦 𝜎𝑑𝜖 resilient materials
are those with high yield strength and a low modulus of elasticity. High carbon steels have a high
resilience and low carbon steels have a smaller resilience.
Toughness is measured as the total area under the deformation curves, elastic and plastics
regions of the stress strain curve. In terms it is the measure of the ability for a material to absorb
energy up to the fracture point. Materials that are more ductile tend to have a higher toughness
than those of a higher strength material. Lower carbon steels will be tougher than high carbon
steel. Since high carbon steels have a high strength but low strain they will be considered less
tough.
11.
The reason why Lake Superior ore boats are not made of high strength steel alloy is
because it is more vulnerable to cracking. With the variation in water temperatures the hulls of
the ore boats tend to shrink in colder water and expand in warmer waters of the ocean. With a
low strain rate of high carbon steel there is little leeway for this expansion and contraction to
occur; this in turn would cause the boat to crack under drastic water temperature changes. That is
why ore boats are made of a low carbon more ductile steel over tough high carbon steel.
Aluminum: After tensile test, its
final diameter was the least,
showing that its ductility is the
least.
Final Length: 0.162”
Final Diameter: 2.133”
Brass: After tensile test it was the
most ductile of the three alloys
with a change in length 0.305”.
Upon observation it is seen that the
brass broke the most smoothly and
also has the smallest final diameter
Final Length: 0.147”
Final Diameter: 2.154”
Steel: After tensile test a large cup
and cone at the fracture point was
observed. This shows that the
ductility in the steel is low than
that of the other metals.
Final Length: 0.162”
Final Diameter: 2.154”
Conclusion: