Testing the stamina of a stuff can assist happen the many mechanical belongingss that exist, this is of import to detect due to the frequent usage of metals in industry. Tensile strength measures the maximal sum of emphasis that can be applied to a stuff without break [ 1 ] . A tensometer is used to fracture the sample. The passage from an elastic, to a fictile stuff can be plotted on a emphasis vs. strain graph. Some steels have a output strength which can besides be plotted on a graph. The output strength is the maximal emphasis burden which can be applied to a metal before it is for good deformed ; it is conveyed in the signifier of upper and lower output points.
In add-on to this, the ductileness of a metal can be measured in the signifier of elongation and decrease in country at break. When a metal has been fractured, if it has no plastic distortion so it is said to be brickle and if it has experienced some fictile distortion so it is called malleable [ 2 ] .
The per centum of elongation is a measuring of how much the break length has increased, if at all ; this identifies the ductileness of the metal. The length of the metal is measured before and after break, to give the per centum of elongation. Consequently, the longer the sample post-fracture, the more ductile the metal is.
The per centum decrease in country is the alteration in the cross-sectional country of the sample. The cross-sectional country is measured before and after break, if the metal is malleable so the cross-sectional country will hold decreased in comparing to the original value measured. The ground that there is such a lessening in the cross-sectional country at the point of break is due to the “necking” which occurs. Below is a diagram demoing an illustration of this:
The diagram [ Figure 1 ] shows an illustration of what a sample expressions like before break, followed by a sample after it has been fractured by the tensometer.
This experiment is to find the belongingss of different metals. The three samples being used are annealed mild steel, bright drawn steel and 60/40 Brass. Each of these will be put through a tensometer to mensurate the upper limit burden which can be applied to them before break. After they have been fractured, the ductileness of each sample will be measured. In add-on to this, other belongingss will be uncovered about how the metal was produced.
Three metal samples are tensile tested utilizing a tensometer. Each sample is about 20mm2 and has different calibrated burden cell demands ; Bright drawn steel ( 20kN burden ) , 60/40 Brass ( 10kN burden ) and Annealed mild steel ( 10kN ) . 60/40 Brass is a combination of 60 % Cu and 40 % Zn [ 3 ] ; therefore it is an metal. Both annealed steel and bright drawn steel have different composings of C and Fe, in add-on to this they are manufactured through different methods to accomplish different mechanical belongingss.
The trial pieces are dumbbell shaped as shown below: ( These can besides be seen in [ Figure 1 ] on page 2 ) .
First, the diameter of each sample is measured three times ; an mean diameter value was so calculated. From the diameter, the cross-sectional country of each sample is calculated. In add-on to this, the length of the sample is measured.
Next, the metal sample is secured into the tensometer. The x.y.plotter is set to zero and graph paper put in topographic point ready for the tensometer to plot the activity. The grip of the tensometer is turned until the metal fractured. A burden vs. extension curve needs to be plotted on the graph ; it is plotted up until the break occurs.
[ Table 1 ]
Bright Drawn Steel
( millimeter )
Average Diameter ( millimeter )
Cross-sectional country ( millimeter )
Maximal Load ( kN )
Elongation ( % )
Decrease in Area ( % )
Ultimate Tensile Strength ( N/mm2 )
Output Strength ( N/mm2 )
Proof Stress ( N/mm2 )
Above, [ Table 1 ] has all of the consequences obtained from the experiment ; they show that the most malleable metal sample is annealed steel, followed by 60/40 brass and bright drawn steel, severally. See the affiliated graphs [ 1, 2 and 3 ] for consequences of the x.y.plotter.
On the following page are the expressions used to happen the consequences in [ Table 1 ] :
Area=?r2 Reduction in Area % = Reduction in cross sectional areaOriginal cross sectional country x 100
Elongation % =Increase in gauge length at fractureOriginal gage length
Tensile Strength= Maximum LoadCross sectional country
Output strength=Load at the lower output pointOriginal cross sectional country
Proof Stress=Load to bring forth a lasting addition in the gage length by a specified amountOriginal cross sectional country
Normally, a 0.1 % cogent evidence emphasis is measured ; this is because the tensometer ‘s used are much bigger in industrial usage. In the lab a much smaller tensometer was used so for this ground a 1 % cogent evidence emphasis was calculated for better truth.
Bright drawn steel –
From [ Table 1 ] , it is clear to see that this sample is non every bit ductile as the other two samples. There is no output point drawn on the graph [ Graph 1 ] , alternatively the cogent evidence emphasis was calculated. This is the point at which the metal begins to deform. Bright drawn steel is most normally cold worked [ 4 ] . Cold working forces the grains to be closely jammed which consequences in the metal being stronger. Below is an illustration of how the grains will alter from mild steel ( left side ) to bright drawn steel ( right side ) through cold working:
60/40 Brass –
This specimen of brass ( 60 % Copper, 40 % Zinc ) , holds really malleable belongingss as can be seen in [ Table 1 ] . The output strength could non be measured here because there is no clear boundary between the elastic and fictile parts on the graph [ Graph 2 ] .
Annealed Mild Steel –
On the extension/load graph for annealed steel, [ Graph 3 ] , it is clear to see the output point. This has been labelled as upper and lower output points, one time the specimen has entered the upper output point it has entered the began distortion into a plastic. Mild steel has low C content, it has about 0.1 % .
The procedure of tempering means the steel goes through several procedures. First, the steel is cold worked to bring forth bright drawn steel. This has made the steel much stronger, harder and less ductile. Following, the bright drawn steel is so heated at a temperature of about 800oC, one time it has been heated it is left to chill to room temperature [ 5 ] . As the steel is chilling easy, recrystallisation occurs and the slow chilling means the equiaxed grains can organize. This is annealed mild steel, after it has cooled it will derive its ductile belongingss.
From this experiment it is clear to see that all metals hold different mechanical belongingss and the belongingss of a metal are dependent on the manner in which they were manufactured. A little fabrication procedure can significantly alter the belongingss of these metals. It has become evident that non all metals have a output point.
[ 1 ] Callister, WD & A ; Rethwisch, DG 2008, Third Edition, p. 200, Fundamentalss of Materials Science and Engineering, John Wiley & A ; Sons, Asia.
[ 2 ] Callister, WD & A ; Rethwisch, DG 2008, Third Edition, p. 203, Fundamentalss of Materials Science and Engineering, John Wiley & A ; Sons, Asia.
[ 3 ] Davies, AC 1971, p113, The Science and Practice of Welding, Cambridge University Press.
[ 4 ] Timings RL 2002, p75, Engineering Fundamentals, Newnes.
[ 5 ] [ 1 ] Callister, WD & A ; Rethwisch, DG 2008, Third Edition, p. 575, Fundamentalss of Materials Science and Engineering, John Wiley & A ; Sons, Asia.
[ Figure 1 ] Czichos, H, Saito, T & A ; Smith L 2006, p. 303, Springer Handbook of Materials Measurement Methods, Springer.