Summary:
The experiment was on tensile properties of various metallic materials. It looked in account the properties of the mild steel, aluminum, copper and brass. The main variables were the load in kilo Newton and the displacement achieved in each case. The displacement is in millimeters. The different metals due to their properties responded differently to the stress caused to them by the loads. This leads to the gaining of the fundamental observations on the axial gauge length, rate, maximum displacement, and extension at maximum displacement and the load at the maximum tensile stress. Consideration of the filleting is important on the brittle materials, as they tend to fracture in poorly prepared materials.
Introduction:
The tensile test is the normally test utilized in the examination and indication of the strength and ductility of the materials. Tensile testing is based on the engineering design experiments. In the tensile testing, appropriate devices are subjected to the gradual escalating uniaxial load in anticipation of the failures takes place within the respective materials. The extensometer is utilized in the measurement of the prevailing functional load for the suitable extensions. Moreover, the tabulated data is graphically represented as a plot of load against the extensions. The load deflection characteristics are normally dependent on the prevailing specimen size. In order to minimize the prevailing geometric factors, load and the corresponding elongation are normalized to the engineering stress accompanied by the engineering strain. The central portion of the existing test piece length is condensed in the cross-sectional area to ensure that the yielding and the corresponding fracture. These features normally occur within a region where stresses are not changed by the prevailing gripping devices. The existing transition from the ends to the reduced section is made through the employment of the sufficient fillet to avoid stress-concentrations basis by a rapid alteration of section.
Theory:
Design mechanical structures fail due to errors in the estimation or the approximation of the strengths of the materials applied in the case of study. The tensile test facilitates the determination of the strength or the ductility of the materials. The tensile test involves the holding of a test piece on an increasing uniaxial load. At the point where the failure occurs, the data is noted. Observations are on the extension against load applied. There is need to reduce load deflection challenges emerging from the analysis. This is only possible on the normalization of the geometric factors, load and the extensions. They are normalized to engineering stress and the engineering strain respectively. Reduction of the central portion at the cross sectional areas facilitate the yielding and fracture at the region of the stress application. Adequate filleting is vital for the maintaining qualities for the assessment of the stress concentrations.
The observations facilitate the design of stress-strain graphs for the materials. The slow or gradual loading of the materials creates two graphs. These are the non-yielding and the yielding.
a) Yielding b)non-yielding
The non-yielding has two extensions. These are elastic and the plastics. The point at which a material extends plastically or breaks abruptly for the ductile materials gives the yielding force.
Aim:
The main of this report is to determine the yield point of different metals when load of similar magnitude is placed on them. This will consequently produce a viable tensile test of the materials involved such as copper, aluminum, brass and Mild steel.
Procedure:
A 30kN universal Testing Machine was utilized in the conduction of the tensile test on the prevailing test pieces of metals specimen. The appropriate specimen information pertaining to the material characteristics such as cross-sectional area, gauge length and crosshead speed were recorded. Then the set up were arranged as stipulated in the laboratory manual.
Before the test
1. Put gage marks on the prevailing specimen
2. Measure the initial gage length and diameter
3. Select the suitable load scale to deform and fracture the existing specimen.
During the process of the test
1. Record the maximum load
2. Carry out the test awaiting fracture
After the test
1. Measure the prevailing final gage length and the corresponding diameter. The diameter ought to be measured from the prevailing neck.
Results:
The tabulated data were utilized in the plotting of the graphs of the respective specimens. The graphs for the respective metal specimens
Test piece and composition E[GPa] YS[MPa] UTS[MPa] Fracture Stress[MPa] Elongation[%] Fracture appearance
Mild steel(Grade 250) 180 502 860 50 30 Cleavage
Aluminum 6061 69 95 110 29 27 Striations
Copper (C12200) 38.9 70 220 193 40 Streak
Brass(C380) 115 78 250 7.0 Brittle
Graph of copper
Graph for aluminium
Graph of Mild steel 2
Graph of Brass
Discussion:
The analysis of the data results facilitates the design of the graphs above. The response of the materials on slow application of the stress indicates aluminum material extending steeply and steadily until it reaches 3500 Newton. The corresponding length at this point is 9 mm. the on further application of stress elongates up to 33mm. at this point the material elongates further with application of less stress. It finally breaks at 3800newtons having elongated to 43mm.
The stress on the mild steel exhibits a fluctuating response on the application stress on the material. At first, the material resists the stress but on assuming 3000, Newton the slope declines. At about 10000 Newton, the material extends to the longest point and becomes plastic spontaneously. After that, constant stress at 9000newtons causes an increase in length of the material.
The brass material experiences a steady gradual extension with increase in the load. At point, 5300 Newton the material starts extending swiftly with small application of stress. At beyond 6400newtons the material breaks off.
The stress application on copper indicates an elastic extension for the applied force until it reaches 6500. At that point, the material experiences a swift extension with a slight additional stress. Beyond 7000, Newton the material elongates plastically to about 43 mm. beyond point it breaks off.
Appendix
Engineering stress-strain curve
Stress(s) = load (P)/Initial cross-sectional area (Ao)
Strain (e) = elongation of the gage length of the specimen (∆l)/initial length of the gage (lo)
e= ∆l/lo = (l-lo)/ lo
Modulus of Elasticity
E = ∆S/∆e = (S2-S1)/ (e2-e1)
Elongation at the break (%) = ex=100× (lx-lo)/lo
Stress = Force/Area
Strain = ∆ℓ/ℓo
0, 2% offset method for decisive the yield strength
