Steel Reinforcement Tension Test
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Introduction: Steel Reinforcement Tension Test can be conducted in two experiment session: * Two deformed grade 460 high yield steel bars * Two plain round grade 250 mild steel bars Both steel bars conform to the relevant requirements of BS 4449:1988; have a nominal diameter of 20 mm, and a length of approximately 800 mm. Objectives: * Practice tension testing of steel bars as reinforcement for concrete according to Hong Kong current standards. * Determine geometrical and mechanical properties of steel reinforcements including nominal cross-sectional area, yield stress, tensile strength, nominal stress at fracture, and elongation over gauge length, reduction of cross-sectional area at necking section, and modulus of elasticity. * Check compliancy of the determined properties of the steel reinforcements with relevant Hong Kong standards. Apparatus: 1. Testing machine equipped with an extensometer with a plotter for drawing load-extension curve (fig. 1) Fig. 1 2. straight edge (fig. 2) Fig. 2 3. A caliper (fig. 3) Fig. 3 4. A metal saw for making marks on the specimens (fig. 4) Fig. 4 5. weighing equipment (fig. 5) Fig. 5 6. metal ruler (fig. 6) Fig. 6 Procedure: i. The mass (M) and length (L) of the bars were measured. The diameter of plain mild steel bar (Dp) was also measured. Dp is used in this experiment to calculate sectional area for comparison with the area derived from mass. ii. The specimens were slightly scribed at regular intervals using the metal saw. iii. The specimen was clamped into testing machine. iv. The extensometer was mounted on the specimen and the gauge length (Lg)
The differences of the mild steel and high yield steel bars are shown below: Mild Steel High Yield Steel Appearance * Plain * Deformed Composition * Carbon 0.1-0.25% * Mn 0.5% * Carbon 0.6-0.99% * Mn 1.5% Properties * Good machinability * Ductility * Weldability * Toughness * Greater yield strength * Lower ductility Recognition * High density * High stiffness * become rusty easily in damp atmosphere * High density * High stiffness * More springy * More friction Cost * cheaper * comparatively expensive Products * Window frames * Pipes * Rivets * High strength wires * Bolts * Springs 3. Why their loadings are different? There are two factors affect the loadings. Firstly, it is because of the difference on the content of manganese(Mn). Manganese can stiffening the steels and improve the loading capacity. So, high yield steel bars (1.5%) have better loading than Mild steel (0.5%) because of the higher manganese content. Secondly, is because of the appearance. Deformed steel have greater surface area and the uneven surface, it can have more friction than plain steel. The higher friction can be a good support for loading. So, the high yield steel bars take the higher loading. 4. Comparison of the Young's modulus (E) between high yield steel and mild steel The elastic modulus of high yield steel bar is lower than that of mild steel bar. However, it is not reflect the strength of the steel. The modulus of elasticity is to measure the stiffness. It is not related to the strength. As Young's modulus (E)
5. There may be some errors when we are reading the results. We should look carefully on reading of the meter of the machine. It is because the steel bar would drop very quickly when the steel bar has broken and the machine cannot apply the loading of the steel bar.It Will break suddenly on a particular meter and the reading of the meter would not stop when the sample fails. Conclusion: The table has shown the calculated results on nominal Area, yield Stress (nominal), tensile strength, stress at fracture, Young's modulus, percentage elongation over gauge length, percentage reduction of area of samples respectively. Sample Mild Steel High Yield Steel A B C D Length (mm) 800 800 800 800 Mass (kg) 1.9917 1.9917 1.9176 1.9367 Nominal Area (mm2) 317.15 317.15 305.35 308.39 Maximum load (kN) 150.9 142.2 189.8 191 Load immediately before the fracture (kN) 128 124 125 139 Extension (mm) 35 33 22 23 Diameter after stretching (mm) 13.95 14.62 12.97 13.19 Cross sectional area after stretching (mm2) 152.84 167.87 132.12 136.64 Yield stress 280.62 277.47 514.16 518.82 Tensile strength 475.8 448.37 621.58 619.35 Young's modulus 192915.08 210311.89 173960.05 184619.73 Stress at fracture 403.59 390.98 409.37 450.73 % elongation over gauge length (%) 35 33 22 23 % reduction of area (%) 51.81 47.07 56.73 55.69 After the steel reinforcement tension test, we found that high yield steel has higher loading capacity compared with mild steel bars. It is shown in the part of yield stress, tensile strength, modulus of elasticity, percentage elongation, reduction of cross-sectional area and the part of nominal stress at fracture. The uneven surface of the high yield steel bars provided more friction and hardness. ?? ?? ?? ??
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