Department of Mechanical & Manufacturing Engineering, Faculty of Engineering, UPM

Course: Strength of Materials 1Course Code: EMM 3108Session: Semester 2 (2014/2015)

Report Title: Impact Test

Group Members: NameMatric No.Signature

Muhammad Asyraf Bin Muhammad Rizal

180732

Vinod Raj A/L Senivasagam

180720

Muhammad Redzuan Bin Kamaruddin

180590

Date: 6/3/2015Date Submitted: 13/3/2015Lecturer Name: Dr. Che Nor Aiza JaafarDemonstrator Name: Riadatul Akmal Binti Mohamad Rushdi

IntroductionImpact test of metals provides information on failure mode under high velocity loading conditions leading sudden fracture where a sharp stress raiser, notch is present. The energy absorbed at fracture is generally related to the area under the stress-strain curve which is termed as toughness in some references. [2] Brittle materials have a small area under the stress-strain curve which is due to its limited toughness and as a result, little energy is absorbed during impact failure. As plastic deformation capability of the materials or ductility increases, the area under the curve also increases and absorbed energy and respectively toughness increase. The impact test helps to determine the ductile to brittle transition using V notch and U notch Charpy impact test.[4]

Objectives Students are required to study the principle of impact testing using metals which are susceptible to brittle fracture. (Mild Steel and Carbon Steel) Students are capable of interpreting the obtained experimental data for the selection of engineering materials.

Procedures1) The thickness of the specimen and the dimension of the unnotched is measured length are measured.2) A pendulum is raised to left until it is indicated to the maximum energy which is ranged based on the upper indicator unit.3) A specimen is placed horizontally across the supports with the notch away from pendulum. 4) The pendulum is released by pushing up on the hand released.5) The pendulum is dropped and strike the specimen. 6) The indicator is moved and stopped when peak swing is registered that provided a direct reading of the energy absorbed.7) The indicated value is recorded and tabulated.8) The brake is applied until the pendulum returned to its stable vertical hanging vertical position.9) The specimen is removed from the testing area and the failure surface is observed.10) The test is repeated with other material and notch.

ResultsTable 1: Experimental resultNotch TypeV- NotchU- Notch

MaterialMild SteelCarbon SteelMild SteelCarbon Steel

S0 [mm2]0.4210.3750.2850.300

ARi[J]i=1i=2i=3i=1i=2i=3

5.004.954.954.955.004.95

ARm [J]4.9674.967

Akabg [J]>25.05.9>25.05.25

Ak [J]20.030.93320.030.283

ak [J/cm2]47.582.48870.2800.943

Calculation

(ARm) u-notch = 4.967 J(ARm) v-notch = 4.967 J

(Ak) v-notch, mild steel = 25 - 4.967 = 20.033 J(Ak) u-notch, mild steel = 5.9 - 4.967 = 0.933 J(Ak) v-notch, carbon steel = 25 - 4.967 = 20.033 J(Ak) u-notch, carbon steel = 5.25 - 4.967 = 0.283 J

(ak) v-notch, mild steel = = 47.58 J/cm2(ak) u-notch, mild steel = = 2.488 J/cm2(ak) v-notch, carbon steel = = 70.288 J/cm2(ak) u-notch, carbon steel = = 0.943 J/cm2

Discussion1. Compare and discuss on the impact work values for each specimen with the theoryFrom the results of the experiment, we can see differently how the specimens fracture. By comparing all the specimens used, we can conclude that the best specimen that gives highest impact energy is mild steel (v-notch). We can also conclude that mild steel is tougher than carbon steel and the v-notch provides better performance against impact. The more energy absorbed by the specimen, the more toughness the materials that will be. [1]2. Discuss on the fracture surface of the tested specimensBy observing the surface of specimens, we see that the carbon specimen broke completely into 2 parts and the broken surfaces looks smoother than the mild steel. This happened due to the ductileness of carbon is lower than mild steel. A higher toughness material will absorb more energy upon impact and will therefore result in a low height to which the pendulum arm will swing to following impact. The more energy absorbed by the specimen, the more toughness the material will be. Specimen with lowest absorbed energy means its brittle and has least toughness which can break easily and cannot withstand the sudden high loads. Specimen with Highest absorbed energy means its ductile and has highest toughness which can withstand the sudden high loads. [2]3. Discuss on the factor that can be affected to the experimental result.There are two possible factor that can be affected to the experimental result which is;I. SpecimenMore energy needed in the ductile fracture because it is a tough material.

II. EquipmentBrittle fracture happens quickly without warning while the ductile fracture took a longer time before the whole process to happen.

Conclusion

Impact is a high force or shock applied over a short time period. Such a force or acceleration can sometimes have a greater effect than a lower force applied over a proportionally longer time period. At normal speeds, during a perfectly inelastic collision, an object struck by a projectile will deform, and this deformation will absorb most, or even all, of the force of the collision. Viewed from the conservation of energy perspective, the kinetic energy of the projectile is changed into heat and sound energy, as a result of the deformations and vibrations induced in the struck object. However, these deformations and vibrations cannot occur instantaneously. A high velocity collision which is an impact that does not provide sufficient time for these deformations and vibrations to occur. [3] Thus, the struck material behaves as if it were more brittle than it is, and the majority of the applied force goes into fracturing the material. From the impact test that we have done, carbon steel undergoes brittle fracture while the mild steel undergoes ductile fracture. More energy is absorbed by mild steel shows that it is more suitable to be use in the structural construction that expose to high load for example vehicles body such as car body or bus body.

References

[1] R.C. Hibbler. 2012. Mechanics of Materials. New York: Pearson Education Inc. [2] Charpy Impact Test accessed on 08/03/2015 available from en.m.wikipedia.org/wiki/Charpy_impact_test[3] Impact on Mechanics accessed on 08/03/2015 available from en.m.wikipedia.org/wiki/Impact_(mechanics)[4] The Charpy Test and Drop Weight Method accessed on 07/03/2015 available from http://www.labtesting.com/services/materials-testing/mechanical-testing/impact-testing/

Appendix

Figure 1: Impact Test Results