fracture lab report 1

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School

University of New South Wales *

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Course

1101

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Material Science

Date

Oct 30, 2023

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pdf

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UNSW Sydney School of Materials Science and Engineering Fracture of Materials Submission Sheet I declare that this is my own work. Name: Kayla Huang Student No: z5479232 Date: 23/10/23 Lab instructor: Ziheng Feng Group: Mark:

Complete the table below using the data emailed to you For the measured values, take the average of the data collected in class, and also determine the average fracture load and the error (standard deviation) in this measurement. Use these values to calculate your answers for the rest of the table. Measure Calculate Failure mode B (mm) W (mm) b (mm) Fracture load (kN) Fracture stress (MPa) a (mm) Predicted stress for failure by fast fracture (MPa) Average Error Unnotched 4.4 2.63 0.599 0.0255 51.7 General yield fracture Notched 4.46 5.53 2.84 0.409 0.00351 32.3 0.81 26.5 Fast fracture Was there a difference in the failure mode of the samples? Yes. If so, explain why? The stress for the notched sample concentrates at the notch’s point, creating an artificial crack, during the fast shattering of the notched sample. The stress required to fracture the material is less because the crack is much more evident on a macroscopic scale. Additionally, the notched sample produces a cleaner fracture surface since the crack, would spread quickly between the two notches as stress is being focused on the fractures rather than the microscopic imperfections in the material. This would result in a considerably smoother surface as there would be less time for interior flaw fractures to appear. The unnotched sample contains a rough and uneven surface, while the notched sample has a cleaner failure section. This is because overall yielding occurred in the unnotched sample while rapid fracture occurred in the notched sample. Yielding in the unnotched sample would cause the stress to concentrate in the material’s microscopic internal imperfections and air pockets. Due to uneven distribution of the internal imperfections, the material would shatter at the stress concentrations under a tensile force, resulting in appearance of an uneven surface. The uneven yielding pattern of the material would subsequently be created when the cracks spread in random directions.

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