ABSTRACT out a tension test one needs
ABSTRACTThetensile strength of an example of AISI 4340 steel was measured using an IntronModel 4400 Series load frame. This test was carried out in order to determinesome basic properties of the 4340 steel. It was determined that the steel had aYoung’s modulus of 245 GPa, an ultimate strength of 723 MPa, and a fracturestrength of 562 MPa. These values yielded a relatively low percent errorcompared to known values of the 4340 steel.
This proves the validity of thetest instruments as well as the data evaluation. 1.Introduction1.
1Tension Testing Tensionstests are carried out on samples of materials to determine basic propertiesthat come about by applying tension on a material. This is important tounderstand because it determines the strength of a material as well as how ituniquely performs under stress. Some ofthe properties that can be determined by these tests are the Young’s modulus,fracture strength, and the ultimate strength. These three properties arecrucial to understanding a material and knowing its appropriate use. Inorder to carry out a tension test one needs to use an instrument capable ofapplying a specifically measured tension force to two opposite ends of amaterial. Additionally, instruments need to be available which accuratelymeasure the change in length of the material. Knowing the force applied and thechange in length at a given time provided all the data necessary in order tomeasure key properties of a material.1.
2Young’s ModulusThe Young’s modulus is alinear relationship between stress and strain that can be seen at the beginningof a tensile load of a ductile material. It defines a region of loading for amaterial where as long as the load does not surpass the yield strength, thematerial will return to the shape it had prior to the loading with no permanentdeformation. Once the load surpasses the yield strength the material will havepermanently deformed, and the linear relationship will no longer exist. Thestress involved in the Young’s modulus is defined by the following formula whichis a relationship between force and area:Furthermore,the Young’s modulus is a simple was of defining the stiffness of a material, ora materials resistance to deformation as a material with a higher Young’smodulus will deform less with a strain than would a material with a lowerYoung’s modulus.
The strain used in determining the Young’s modulus is therelation between deformation and the original length of the test object definedby the following relationship:Using the definitions ofstress and strain the Young’s modulus can be understood with the followingformula: WhereE is the Young’s modulus measured in GPa, ? is the stress measured in MPA, and ? is the strain, measured in mm/mm. 1.2Ultimate and Fracture StrengthOnce a material hassurpassed its yield strength it has moved past the region defined by theYoung’s modulus. It is in this region that a material will deform untileventually it fractures. Instead of a linear relationship, this region isdefined usually by a parabola, peaking at the tensile or ultimate strength. Theultimate strength is the largest load a material can handle before the strainbegins increasing with a. decreasing stress. This ultimately leads to afracture of the material.
The region following thelinear Young’s modulus can appear to have many shapes. A brittle material willfail quickly and tends to have the fracture strength and the ultimate strengthvery close to each other. On the other hand, a ductile material will still havea relatively large region between the ultimate strength and the fracturestrength. 2.Experimental Procedures2.1Materials and EquipmentA Instron 4400 seriesload frame was used on a sample of AISI 4340 steel to perform the tensiletesting in this laboratory. AISI 4340 steel is a medium carbon known forstrength and toughness.
It is typically used for structural manufactured partssuch as gears and sprockets 2. An extensometer will also be usedin order to accurately measure the change in distance of the materialdeformation. 2.2Experimental PreparationsFor this experiment itimportant to take some precautions as with any experiment that involvesfailures under loads.
Safety glasses and clothing were worn at all times in thecase of extreme failure of the material.2.2Testing ProcedureFirst, the initialmeasurements of the material were recorded. This meant the initial dimeter ofthe rod as well as the initial length of the material. Then, the rod was loadedinto the load frame and the extensometer was attached. Once everything isloaded as it would be for the test the instruments were zeroed and the testingbegan. The load frame applied an increasing load to the rod until failure ofthe rod was achieved.
Once the test material fails it is unloaded from the loadframe and premeasured for the fractured diameter. 3.Results3.1Tension TestUsing equation (1) tomeasure the stress on the rod combined with the strain data given from theextensometer the graph in Figure 2 was constructed to demonstrate the stressversus strain relationship of the material. The material failed under a fracturestrength of 562 MPA while achieving its largest load at 723 MPA.
The linearrelationship of the Young’s modulus was clearly defined in the beginning of thegraph, leading to the calculation of the Young’s modulus to be 245 GPa. Thestress versus strain relationship followed a predictable and well-definedpattern. The material had a linear stress versus strain relationship until theyield load was reached. After this point the graph followed a parabolic curvewhere it achieved the ultimate strength at the maximum of the curve. At the endof the curve where the parabola cuts off is where the material completelyfailed, giving us the fracture strength of the material. Upon comparison withknown values for 4340 steel the results appeared relatively accurate.
While theYoung’s modulus was off by approximately 14% the ultimate strength was off theknown value by 3% 1.4.DiscussionComparatively, the knownvalues for 4340 steel and the results of the laboratory were very close. 14%for the Young’s modulus is high but not high enough to question the validity ofthe results. This difference could be due to the fact that the best fit linehad outliers in the data and the average skewed the result slightly. Additionally,the ultimate strength only being off by 3% is a very accurate result whichgreatly confirms the validity of the laboratory.
Furthermore, the graph inFigure 2 that the data produced was a highly accurate and very predictablecurve. The behavior of the material based on the data was a perfect match tothe ductile material we knew the material to be. 5.
Conclusion1. The yield strength of this sample of 4340 steel was562 MPa, the Young’s modulus was 245 GPa, and the ultimate strength of thematerial was 723 MPa.2. AISI 4340 steel is a ductile metal.6.AcknowledgementsThank you to theMechanical Testing Instructional laboratory (MTIL) at the University ofIllinois Urbana-Champaign for providing the materials, equipment, and expertisenecessary to compile the data necessary for this report. 7.References1.
AZoM. (2013, July 11).AISI 4340 Alloy Steel (UNS G43400). Retrieved January 30, 2018, from https://www.asom.com/article.
aspx?ArticleID=67722. 4340 (E4340) Alloy Steel.(n.d.). Retrieved January 30, 2018, fromhttp://www.benedict-miller.com/content.
cfm/AQ-Steel/4340-Steel/category_id/102/page_id/112 3. J.S. Popovics, L.J. Struble, P. Mondal and D.
A. Lange, CEE300/TAM324 Behavior of MaterialsUniversity of Illinois at Urbana-Champaign : College of Engineering, Spring2018. AppendicesA.1Tables and FiguresTable 1- Tensile mechanicalproperties Quantity Symbol Units Lab Expected Percent Difference Young’s Modulus E GPa 245 210 14.3% Ultimate Strength ?u MPa 723 745 3.04% Fracture Strength ?f MPa 562 – – Figure 1: Nominal tension specimendimensions (mm).Figure 2. Graph of Engineering Stressversus strain for 4340 Steel.
E.3Sample CalculationsE.3.1Tensile StrengthOne of the most important measurements to determine isthe stress on the material. Engineering stress is found by the simple formula:Where ?is the stress, F is the load force and A is the cross-sectional area of thetest material. Using this relation, we can measure the stress of the material:E.
3.2Young’s ModulusA key measurement to be made is the Young’s modulus,the measurement of the stiffness of a material. The young’s modulus defines amaterials ability to return to its original shape and strength after a certainload has been applied. The Young’s modulus can be found with the followingformula:with the E representing the Young’s modulus, the ? representing the stress, and the ? representing the strain. Using the data given formthe laboratory we can calculate the Young’s modulus.