en.pdf Experimental testing of mechanical properties of materials

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1 Materials (18MTY) Winter term 2018/2019 lectures: MSc. Jaroslav Valach, Ph.D. practicals: MSc. Petr Koudelka en.pdf 1 Main topics Mechanical properties of materials Experimental testing of mechanical properties of materials The main classes of materials Defectoscopy Degradation of materials 2 Main goals of the course Student will obtain a general overview of technically important materials (metals, polymers, and composites). The basic level materials science course builds a consistent explanation of materials from the level of atomic level to practical procedures during technological processes and material production. He/she will also understand decisive mechanical properties of materials for engineering and technology on the basis of hands-on practicing of the most important mechanical tests like tensile test or hardness test. 3 Literature W.D. Callister, Jr.: Materials science and engineering: an introduction. John Wiley & Sons Topics of lectures Mechanical properties of materials, goal of materials science. Structure of materials. Crystal structure, lattice defects. Solid solutions, thermodynamics and binary diagrams. Steel and cast iron, quenching, tempering, annealing. Fe-C diagram, special steels and alloys. Non-ferrous metals. 1

2 Polymers, structure, processing, mechanical properties. Glass and ceramic, major use, explanation for strength and fragility. Composites - properties, advantages, synergies, fibers and matrix. Degradation of materials, nondestructive testing. 5 Schedule of practicals 1. Conditions for course credit assignment, safety rules in the Laboratory of experimental mechanics, introduction to mechanical testing of materials, uni-axial tensile test Mechanical testing of materials uni-axial test, hardness test, Charpy impact test. 6 Organization of practicals in Laboratory of experimental mechanics The group of students will be divided into three measurement sub-groups of at least two and maximum five students. Each measurement sub-group will study theory of every type of laboratory measurement with emphasis put on directly measured quantities (including units), derived quantities as defined in test assignment (including units), and mathematical relations for evaluation of the test. In the beginning of measurement practicals, the knowledge of students will be checked by the teacher and the group will then begin with preparations for the measurement according to manual in the test assignment. The students will without exception obey instructions given by the teacher to follow the safety rules and to avoid damage to the testing machines. Steps, where the explicit approval of the teacher is required, are in the test assignment highlighted in bold font. After the measurement, the teacher will sign any values measured by the students that will be used during evaluation of the test. 6.1 Laboratory protocol Example of laboratory protocol can be found at: pdf/view 6.2 Schedule of laboratory measurements The group of students will be divided into three measurement sub-groups, where the number of the sub-group will serve as a key to order of test performed in the Laboratory of experimental mechanics. Schedule is shown in Tab. 1. 2

3 Measurement sub-group no. 20 November December December tensile test hardness test impact test 2 impact test tensile test hardness test 3 hardness test impact test tensile test Table 1: Schedule of measurements in the Laboratory of experimental mechanics 7 Conditions for course credit assignment 1. Delivery of all laboratory protocols and individual exercises in final form approved by the teacher. Assignments of laboratory measurements and individual exercises can be found in Appendix. 2. All conditions have to be met at the latest on 8 January Exam 8.1 Organization of exam 1. Valid course credit assignment is required for registration to exam. 2. The exam is composed of written and oral part. Satisfying the conditions for pass in the written part is mandatory prior to the oral part. 3

4 A Assignments of laboratory measurements and individual exercises A.1 Uni-axial test Perform quasi-static uni-axial test and evaluated the measured data. Determine ultimate strength, yield strength, ductility, and Young s modulus. Use long gauge length. A.1.1 Measurement system and tools Testing system Instron 3382 (control software Series IX) Vernier caliper (a) Electro-mechanical testing system (b) Specimen Figure 1: Tensile test A.1.2 Measurement procedure Measure cross-section of the specimen. Mark the gauge length on the specimen. 4

5 Fix the sample in the grips. Ask the teacher to start the test. Save the acquired data. Measure length of the sample after the breakage. 5

6 A.2 Hardness test Perform Vickers hardness test, evaluate Vickers hardness, and correctly write the result. Perform 10 measurements using the provided sample, calculate the average value and the standard deviation. A.2.1 Measurement procedure Turn on the illumination of the testing machine. Put the specimen on the table of the hardness testing machine. By turning the wheel, set height of the table so that sharp image can be seen on the ground glass. Based on instruction of the teacher, press lever 1. After the prescribed duration of the test, press lever 2. Measure diagonals of the imprint using image on the ground glass. Figure 2: Vickers hardness testing machine 6

7 (a) Ground glass with Matnice s movable gauges (b) Detail of the imprint (captured using scanning electron microscope) Figure 3: Vickers hardness test A.3 Charpy impact test Perform the Charpy impact test. Use a room temperature sample and a frozen sample. Evaluate impact energy for both specimens and the resulting toughness. Correctly write the results. A.3.1 Measurement device and tools Impact test machine Vernier caliper Freezer spray A.3.2 Measurement procedure Measure dimensions of the specimen. Place the sample on supports of the testing machines. Reset the gauge. Based on instruction of the teacher, put the hammer into initial position and secure the ratchet. Ask the teacher to release the ratchet. Write down the measured energy of the hammer after test. Perform calibration test without the specimen to evaluate mechanical losses. The ratchet will be released by the teacher! 7

8 (a) rest position (b) before start of the test Figure 4: Impact test machine (a) Intact specimen (b) Specimen after test Figure 5: Specimen for Charpy impact test A.4 Individual exercise 1 Evaluate theoretical density of material given in the table 2. Obtain the required data from a trusted source and provide citation. Properties of the crystal structures are temperature dependent. Provide information on temperature, for which the theoretical density is calculated. Month of birth January February March April chem. element Ni Au Ir Pd Month of birth May June July August chem. element Al Cr Pb W Table 2: Chemical elements for exercise 1 8 Month of birth September October November December chem. element V Mo Ag Li

9 A.5 Individual exercise 2 Describe phases present in the alloy as defined in figure 6 with chemical composition given by equation 1 and temperature given by equation 2. Determine relative ratio of these phases in the solid solution at the given chemical composition and temperature (use the lever rule). Determine the average density of the solid solution with the given chemical composition at room temperature. Consider homogeneous distribution of phases in the whole volume. Obtain density of chemical elements Sn and Pb in a trusted source and provide citation C L 232 C α 183 C L+ α L+ β β T [ C] α+β 0 100%Sn 100%Pb hm. %Pb Figure 6: Eutectic equilibrium phase diagram X = 10 + day of birth < 1; 31 > 0.45 [hm.%pb] (1) T = 80 + month of birth < 1; 12 > 0.12 [ o C] (2) 9