Material Selection in Design and Engineering - Research Paper Example

Table of contents ………………………………………………………………………………………..3 Introduction………………………………………………………………………………………3 Theory…………………………………………………………………………………………...4 Experimental procedure………………………………………………………………………….7 Results and data analysis………………………………………………………………………....9 Discussion………………………………………………………………………………………16 Conclusion……………………………………………………………………………………....18 References……………………………………………………………………………………….19 Abstract Engineering materials knowledge is very important for a good foundation in mechanical engineering. A good and strong foundation in engineering materials leads to a good student interest and follow up courses such as in design. Laboratory experiments are normally carried out to determine the physical properties of materials. Naturally, many aspects of nature exposed to a material. Tensile, compressive and shear among others are some of the forces applied in a material (Broughton and Sims, 1994).These aspects are very crucial and vital in material selection for any design especially in engineering. Cost is another factor that must be considered in material selection. Primarily, pearlitic and bainitic steels are some of the cheapest materials also applicable in many fields. Different methods are used to tamper with the strength of the material. Some of the methods are illustrated below. Introduction Tensile-impact test is used for the determination of toughness properties of polymeric materials for which the performance of the instrumented Charpy impact test is not possible because of the specimen thickness and/or low material stiffness. This method is applied especially within testing of polymeric sheets and elastomers. Examinations for determining the toughness are performed with the pendulum de- vice Resil Impact or Junior 25 according to (ISO 13802, 1996). This pendulum device has a works with capacity of 4 J, 7.5 J, 15 J and 25 J at maximum falling angle of 150°. In this test, a specimen is fixed between a stationary clamp and a cross head. In contrast to Charpy impact testing, while undertaking notched tensile-impact testing, there is no direct contact of the pendulum hammer and the specimen takes place. The pendulum hammer hits the cross head which is fixed to the specimen. In this way, the specimen is deformed in direction of its longitudinal axis until fracture occurs. Theory Tensile-impact test Therefore, a tensile-impact test with specimen which unnotched is a uniaxial tensile test with a high deformation speed. The metallic pendulum hammer consists of a tubular pendulum arm and an impact construction with metallic blocks at both sides, which meet the cross head. After release, the pendulum hammer moves in a circle and transfers part of its kinetic energy to the cross head and therefore, indirectly to the specimen, at the lowest point of its trajectory. In short pendulum hammers (up to 4 J working capacity at maximum falling angle), the testing speed at zero crossing is 2.9 m/s. For Larger pendulum hammers, we have a larger pendulum length and therefore, their velocity at the zero crossing is 3.7 m/s. Specimens have a rectangular cross-section and are double-edge notched. Recording of the load (F)–time (t) signal is realized over a load cell, which is integrated in the stationary clamp. We have 4 kN as the measuring range. From the F-t diagrams, the deformation (in this case the extension) can be calculated from Newton’s second law. In a first integration step (1), the velocity can be determined, and in a second integration step (2), the extension l of the specimen as a function of time: ………………………..1 …………………………………2 The tensile strength of ferrous and non-ferrous materials is tested using the tensile testing machine as shown in the Fig1.a below. Figure 1: Tensile testing machine Cross-sectional area and original length of the material sample is measured before clamping it in the tensile testing machine. To stretch the material sample, turn the handle of the tensile testing machine. It is possible to determine the extent of elongation of the sample by reading the value in the elongation meter on the machine. A separate dial on the machine displays the tensile force. Record the tensile force and the degree of elongation of the sample (Zhang et al., 2006). The tensile properties of a material are illustrated using a stress-strain graph. Stress is the force per unit area acting on a material sample. It is always expressed as: Strain is defined as the ratio of the length of elongation to its original length. It is always expressed as: Figure 2 illustrates what happens when a material is stretched. Fig1.c shows the stress-strain graph for mild steel. Point A on the chart is called the elastic limit. This is the maximum level of stress beyond which it will yield to enduring deformation. If the load is removed before the specimen has reached its elastic limit, it will restore to its original length. This stage is called its elastic stage. Beyond its elastic stage stretching results in enduring deformation. This stage is called its plastic stage. If the load is removed within the plastic stage, the increase in length of the mild steel will be reduced, but it will not return to its original length. This means that the internal structure of the mild steel has already been altered. Figure 2: changes in the tensile structure Vickers Hardness Test Vickers hardness test method involves indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136° between opposite faces subjected to a load of 1-100 kgf. The full load is normally applied for 10-15sec. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation. P is the load and it can be varied from 0.1 to 1Kg d is the average diagonal diameter of indentation [m] When the mean diagonal of the indentation has been determined the Vickers hardness is calculated from the above formula. The Vickers hardness should be reported like 600 HV/10, which means a Vickers hardness of 600, was obtained using a 10kgf force. Vickers hardness test produces extremely accurate readings, and just one type of indenter is used for all types of metals and surface treatments. Microstructure observation of ferrous and non-ferrous metals The microstructure of iron-based alloys is very complicated and diverse, being influenced by composition, homogeneity, processing and section size. Microstructures of castings look different than those of wrought products, even of the same composition and if given the same heat treatment. In general, it is easiest to identify heat-treated structures after transformation and before tempering. For example, if a mixed microstructure of bainite and martensite is formed during quenching, these constituents will become more difficult to identify reliably as the tempering temperature given the product increases towards the lower critical temperature. Further, while ferrous metallographers tend to use nital almost exclusively for etching, nital is not always the best re- agent to use to properly reveal all microstructures. It is unfortunate that some companies prohibit use of picral because picric acid can be made to detonate under certain conditions. Picral is an excellent etchant for revealing certain microstructural constituents in steel and accidents have been less common than for nital. Vilella’s reagent, which also contains picric acid, is also exceptionally valuable for certain com- positions and microstructures. 10% sodium metabisulfite in water (10% SMB) is a very good general-purpose reagent for steels, and safer to use than nital or picral, with a combination of the capabilities of both nital and picral (Hojo, Sawada and Miyairi, 1992) Experimental Procedure Tensile testing and impact testing of polymers Equipment-Impact Tester MT 3076 Procedure a) Set the zero point of the start point Because of friction and wind resistance, the pendulum will not have the same striking angle as the fall angle. This can be compensated for by inclining the impact tester slightly. The fall angle will then be larger and the striking angle less but the scale is fixed and a non-loaded blow of 15 joules should show a value of 15 joules. b) Testing Testing is done by the tensile instrument. The sample is normally gripped such that both ends are covered approximately 3mm away from the tester-length. The return button is pressed in the controller section of the instrument for a few seconds until beeping sound is heard. The grips sample will be taken back to the start point automatically. To prevent unexpected experimental errors, the samples should be gripped tightly in order to avoid slipping. The buttons can be pressed either in up or down direction in order to adjust the location and position of the grip on the upper side. The polymer sample is then placedat the lower grip while at the same time holding vertically with the other hand and closed firmly and tightly.as a result, a force in (KN) and stroke (mm) will be obtained during the testing experiment. Tensile testing of ferrous and non-ferrous metals Procedure The strike plate is clamped to the specimen using the wing nut and screw. The pendulum is held securely away from the central region by a solid bar across the frame. The specimen subassembly is attached to the base of the tester using another wing nut making sure the specimen is aligned with the swing path of the pendulum and the strike plates are perpendicular. Now the pendulum is raised to the desired angle and released. The specimen is broken and thrown forward with the swinging pendulum. The swing angle after striking is noted from the tester scale as indicated by the needle arm. The specimen pieces are put together at the fractured location and measured for elongation and reduction in area as measure of ductility. The net energy absorbed is calculated by subtracting energy left over from the starting energy of the pendulum. The test should be repeated multiple times for a given specimen type as the test data varies randomly. Vickers hardness measurement of various engineering alloys Equipment to be used- Zwick Universal hardness tester up to 185kg.Before commencing sample testing, it is necessary to use a calibration block of known hardness to verify that the tester is working properly. Microstructure observation of ferrous and non-ferrous metals Equipment Optical microscope connected via television screen, optical microscopes, eyepiece micrometer, two-wheel metallographic specimen, preparation table, sink. Results and Data analysis Zwick/Roell Pendulum Impact Tester. M/c Model No 5113. Ref No A466690. Force 7.5J Table .1: Material: PVC Specimen width b0 Specimen thickness a0 Cross-section Impact energy Impact energy Impact resistance Type of test, PIT Work contents Material Nr mm mm mm² J % kJ/m² J 1 15.76 3 47.28 0.37 4.88 7.74 Charpy 7.50 2 14.85 2.81 41.73 0.37 4.88 8.77 Charpy 7.50 3 15.12 2.92 44.15 0.34 4.47 7.59 Charpy 7.50 4 15.76 2.77 43.66 0.26 3.46 5.94 Charpy 7.50 Graph .1: graph for PVC Material Failure type 1-4= Brittle Zwick/Roell Pendulum Impact Tester. M/c Model No 5113. Ref No A466690. Force 7.5J Table.2: Material: Nylon Specimen width b0 Specimen thickness a0 Cross-section Impact energy Impact energy Impact resistance Type of test, PIT Work contents Material Legends Nr mm mm mm² J % kJ/m² J “ 1 14.87 3.24 48.18 4.54 60.47 94.13 Charpy 7.50 “ 2 15.31 3.24 49.6 4.85 64.62 97.70 Charpy 7.50 “ 3 16.02 3.19 51.1 2.48 33.07 48.53 Charpy 7.50 “ 4 13.7 3.2 43.84 3.35 44.62 76.33 Charpy 7.50 “ 5 14.36 3.18 45.66 3.59 47.86 78.61 Charpy 7.50 “ 6 13.6 3.02 41.07 2.64 35.14 64.17 Charpy 7.50 Un-Notched Failure type 1-2= Bent, 3-5= Brittle, 6=Bent Zwick/Roell Pendulum Impact Tester. M/c Model No 5113. Ref No A466690. Force 7.5J Table .3: Material: Acetal Specimen width b0 Specimen thickness a0 Cross-section Impact energy Impact energy Impact resistance Type of test, PIT Work contents Material Legends Nr mm mm mm² J % kJ/m² J “ 1 14.32 3.08 44.11 0.69 9.17 15.59 Charpy 7.50 “ 2 15.69 3.07 48.17 0.61 8.13 12.66 Charpy 7.50 “ 3 13.01 3.06 39.81 0.93 12.46 23.47 Charpy 7.50 “ 4 15.09 3.05 46.02 0.77 10.33 16.83 Charpy 7.50 “ 5 15.41 3.07 47.31 0.67 8.89 14.09 Charpy 7.50 Graph 2: graph of Acetal 4ET002 Nylon PA66 and PA66 40%GF (glass fibre reinforced) 1. 50 mm/min, 2. 500 mm/min, 3. PA66GF40 50 mm/min; Secant points 15 and 25 MPa but for PA66GF40 30 and 60 MPa. Table .4: 4ET002 Nylon PA66 and PA66 40%GF (glass fibre reinforced) Specimen width b0 Specimen thickness a0 S0 Rp 0.2 E-Modulus RB W up to Fmax. W up to break Rm  Fmax.  Break Nr Mm mm mm² MPa MPa MPa J J MPa % % 1 10.21 3.2 32.67 28.99 959.14 44.60 18.40 163.37 49.47 26.67 215.18 2 9.9 3.28 32.47 29.19 961.85 41.28 18.32 56.21 51.08 26.61 75.99 3 12.7 3.26 41.4 104.60 6801.18 131.12 7.06 8.03 136.99 3.57 3.91 Table .5:Hardness of carbon steels (load 20Kg) 1st measurement 2nd measurement 3rd measurement 0.1% Carbon 146 143 151 0.2% Carbon 169 161 171 0.4% Carbon 206 211 219 0.85% Carbon 254 260 256 4ET002 Polystyrene (PS) and Toughened PS Both 50 mm/min, Secant points 25 and 35 MPa for PS (1) but for TPS (2) 10 and 18 MPa. Table .6: 4ET002 Polystyrene (PS) and Toughened PS Specimen width b0 Specimen thickness a0 S0 Rp 0.2 E-Modulus RB W up to Fmax. W up to break Rm  Fmax.  Break Nr Mm mm mm² MPa MPa MPa J J MPa % % 1 10.18 4.04 41.94 41.71 3117.21 41.35 0.54 0.78 41.87 0.98 1.26 2 10.18 4.04 41.13 25.47 1596.01 15.03 0.50 19.15 25.52 1.28 53.09 Zwick/Roell Pendulum Impact Tester.Monday, 12 September 2016 M/c Model No 5113. Ref No A466690. Force 7.5J Table .7: Material: HDPE Specimen width b0 Specimen thickness a0 Cross-section Impact energy Impact energy Impact resistance Type of test, PIT Work contents Material Legends Nr mm mm mm² J % kJ/m² J “ 1 14.96 3.03 45.33 1.64 21.82 36.10 Charpy 7.50 “ 2 14.97 3.1 46.41 0.48 6.35 10.26 Charpy 7.50 “ 3 14.69 2.78 40.84 0.65 8.61 15.81 Charpy 7.50 “ 4 15.28 2.99 45.69 0.64 8.54 14.02 Charpy 7.50 Failure type 1-4= Hinged Table .8 F max Fmax dL at F max F Break dL at break Nr MPa MPa % MPa% 1 410.10 410.10 2.1 98.8 3.5 2 537.64 537.64 1.8 141 2.8 3 683.62 683.62 1.7 191 2.8 4 768.67 768.67 1.6 269 2.2 5 1082.99 1082.9 0.9 398 1.2 Graph .3 4ET002 HDPE 1. 500 mm/min, 2-3. 50 mm/min; secant points 10 and 14 MPa. Table .9 Specimen width b0 Specimen thickness a0 S0 Rp 0.2 E-Modulus RB W up to Fmax. W up to break Rm  Fmax.  Break Nr mm mm mm² MPa MPa MPa J J MPa % % 1 9.97 4.06 40.46 18.45 1108.34 14.04 4.41 11.47 28.18 9.08 21.59 2 9.97 4.05 40.38 17.23 12.82 4.17 23.07 25.65 9.58 55.14+ 3 9.95 3.96 39.4 17.14 798.00 7.95 4.37 104.67 25.84 10.15 376.72 Discussion Nylon 66 Polyamide (Nylon) (Type 66, 30-33% Glass Fiber) Many partially crystalline samples of nylon have a milky appearance, and the absence of this milkiness is sometimes cited as evidence of an amorphous structure. Actually, the crystallites in nylon are too small to scatter visible light. The milkiness is due to the presence of spherulites. Optical clarity does not necessarily mean that a specimen is entirely amorphous, but only that it contains no spherulites large enough to scatter light or be seen with a microscope. To a considerable extent, per cent crystallinity and spherulitic texture can be varied independently. PVC The curves and the results from table indicate that when temperatures decreases the load at break increases while on the other hand the overall elongation at break decreases. The behavior can be predicted for PVC since at low temperatures there is greater intermolecular forces. HDPE Temperatures have very low influence on the level impact mark of HDPE. HDPE therefore qualifies to be the most appropriate and suitable for low temperatures applications. Polypropylene β-phase of polypropylene Under proper crystallization conditions (shear, large temperature gradients, or use of β-nucleating agents like quinacridone , the anhydrous calcium salt of suberic acid, and other agents, polypropylene samples with a high content of the β-phase can be made In samples that have been subjected to high shear in the melt the β-phase can be found. Polycarbonate The results of tensile testing. In analysis of the yield strength for the polysulfone blends, it appears that the difference in thickness is significant while the difference in orientation is essentially insignificant within a blend composition. The thicker samples had a consistently higher yield strength for the 0.05 in/min strain rate; however, this relationship does not hold completely true for the 5.0 in/min strain rate samples. The rate of testing is significant for polycarbonate blends. The average values of the yield strength for the 5.0 in/min strain rate were consistently 500 to 6(X) psi greater than for the 0.05 in/min strain rate. Taking the results for the yield strength versus percent composition for a given strain rate as a whole, it is clear that the yield strength increases with increasing composition of polysulfone or polyetherimide if an average value is used for each composition. This increase appears to be linear but an extrapolation to 100 percent polysuifone or polyetherimide underestimates the measured value except for the polysulfone blends at 0.05 in/min strain rate, which overestimates the measured value. Acetal Acetal is a highly-crystalline polymer that has high stiffness and strength without the need for glass reinforcement. It offers an outstanding low and high-temperature performance, good colorability, and good mating with metal and other polymers. Carbon Steel Carbon is an element whose presence is crucial in all steel. Carbon is the principle hardening element of steel. That is, this alloying element determines the level of hardness or strength that can be attained by quenching. Furthermore, carbon is essential for the formation of cementite (as well as other carbides) and of pearlite, spheridite, bainite, and iron-carbon martensite, with martensite being the hardest of the microstructures. Carbon is also responsible for increase in tensile strength, hardness, resistance to wear and abrasion. However, if present in high quantities it affects the ductility, the toughness and the machinability of steel. In the experiment we found out that the percentage of carbon does not affect Young modulus. However it affects tensile strength, in that it increase in %carbon leads to increase in tensile strength. Also increase in %carbon leads to decrease in elongation. Conclusion As evident from the details discussed above, various strengths and properties of materials were determined. Modulus toughness of a material is the minimum threshold energy required to break the sample. Furthermore, it is evident that different materials have different tensile strength. Materials can also be integrated carbon element in order to add strength to the sample. Carbon element has been an important compound and thus applied by many manufacturing companies in order to increase tensile strength, hardness, resistance to wear and abrasion. However, it is important to note that if present in high quantities it affects the ductility, the toughness and the machinability of steel (DIN EN ISO 527-1, 2006) For external temperature in the region, the energy variation in both ductile and brittle materials are very low. Additionally, thicker samplers have relatively higher yield strength compared with thin samples. References DIN EN ISO 527-1, (1996)Plastics-Determination of Tensile Properties, Part 1: General Principles. Zhang J., Shen L., Chun Li W. and Zheng Q. Polymer of Materials Science and Engineering, 2006, 22, 123. Broughton W. and Sims, G. (1994) An overview of Through-Thickness Test Methods for Polymer Matrix Composites, NPL Report DMM(A)148. Hojo M. SawadaY.and Miyairi H.(1992) Effects of Tab Design and Gripping Conditions on Tensile Properties of Unidirectional CFRP in Fibre and Transverse Direction, ECCM Composites: Testing and Standardisation, Amsterdam, The Netherlands. Chaudhary D., Jalland M. and Cser F.(2004) Polymers and Polymer Composites, 2004, 12, 383. Read More