Test on High Strength Deformed Steel Reinforcement Bars

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Purpose of the Test:

This experiment aimed to assess the ability of high-strength deformed steel reinforcement bars (HYSD bars) to withstand tensile loads. Key material properties, including ultimate tensile strength, elongation, yield strength, and more, were determined. The behavior of these deformed bars under uniaxial tensile forces was also observed by plotting stress-strain graphs. These material properties are crucial for designers and quality managers to predict and classify the bars for their intended applications.

Results:

Table 1: Initially Measured Physical Properties of the Deformed Bars

Sl. No.	Length, L (mm)	Weight, W (g)	Diameter (mm)	Area (mm²)	Volume (cm³)	Gauge Length (mm)
1	509	774	16	201.06	102.34	80
2	512	774	102.94
3	503	760	101.13

Sl. No.

Length, L (mm)

Weight, W (g)

Diameter (mm)

Area (mm²)

Volume (cm³)

Gauge Length (mm)

509

774

201.06

102.34

512

774

102.94

503

760

101.13

Table 2: Determination of Properties for the Deformed Bars after UTM Testing

Sl. No.	Initial Diameter (mm)	Final Diameter (mm)	Poisson’s Ratio	Area (mm²)
1	16	10	0.375	201.06
2	16	12	0.250
3	16	11	0.312
Average Values	16	11	0.312	201.06

Sl. No.

Initial Diameter (mm)

Final Diameter (mm)

Poisson’s Ratio

Area (mm²)

0.375

201.06

0.250

0.312

Average Values

0.312

201.06

Table 3: Mechanical Properties of the Deformed Bars

Sl. No.	Ultimate Breaking Load (kN)	Ultimate Stress (kN/mm²)	Displacement at Max. Load (mm)	Initial Gauge Length (mm)	Final Gauge Length (mm)	Elongation (mm)	Strain (%)	Yield Stress (kN/mm²)	Young’s Modulus (kN/mm²)	0.2% Proof Stress (kN/mm²)	Type of Breakage
1	157.7	0.784	34.310	80	94	14	17.5	0.674	228.927	0.6727	Cup and Cone type
2	157.35	0.782	29.150	80	98	18	22.5	0.667	175.53	0.6677	Cup and Cone type
3	157.45	0.783	29.690	80	99	19	23.75	0.671	182.33	0.6709	Cup and Cone type
Average Values	157.5	0.783	31.05	80	97	17	21.25	0.670667	195.5957	0.6704	-

Sl. No.

Ultimate Breaking Load (kN)

Ultimate Stress (kN/mm²)

Displacement at Max. Load (mm)

Initial Gauge Length (mm)

Final Gauge Length (mm)

Elongation (mm)

Strain (%)

Yield Stress (kN/mm²)

Young’s Modulus (kN/mm²)

0.2% Proof Stress (kN/mm²)

Type of Breakage

157.7

0.784

34.310

17.5

0.674

228.927

0.6727

Cup and Cone type

157.35

0.782

29.150

22.5

0.667

175.53

0.6677

Cup and Cone type

157.45

0.783

29.690

23.75

0.671

182.33

0.6709

Cup and Cone type

Average Values

157.5

0.783

31.05

21.25

0.670667

195.5957

0.6704

Discussion:

In HYSD bars, determining the yield strength requires the offset method since they do not exhibit a distinct yield point.

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For this purpose, strain is measured using an extensometer, and stress-strain curves were plotted. Offset values of 0.1 percent (as a warning to remove the extensometer) and 0.2 percent were used for proof stress determination.

Improper test control during yielding can lead to high yield strengths.

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An anomaly in the stress-strain curve of sample 2 occurred due to not removing the extensometer at 1mm, as the warning did not pop up as it did for the first and third samples.

The stress-strain curves for the HYSD bars exhibited typical behavior, with an initial linear region followed by yielding and strain hardening. The absence of a well-defined yield point in HYSD bars necessitated the use of the offset method to determine yield strength accurately. This method provided values for 0.1 percent and 0.2 percent offset, and the average yield stress was found to be approximately 0.670667 kN/mm².

The ultimate tensile strength (UTS) of the HYSD bars was determined to be an average of 157.5 kN with an average ultimate stress of 0.783 kN/mm². The displacement at maximum load ranged from 29.150 mm to 34.310 mm, and the average elongation was approximately 17 mm, corresponding to an average strain of 21.25%. Young's Modulus, a measure of the material's stiffness, averaged at approximately 195.5957 kN/mm².

Sample 2 exhibited an unusual behavior in the stress-strain curve due to the failure to remove the extensometer at the appropriate time, leading to higher yield strength. This discrepancy underscores the importance of precise testing procedures and instrument handling in obtaining accurate material properties.

Conclusion:

In conclusion, the experiment successfully evaluated the mechanical properties of high-strength deformed steel reinforcement bars (HYSD bars). The key findings include an average yield stress of approximately 0.670667 kN/mm² using the offset method, an average ultimate tensile strength of 157.5 kN, and an average Young's Modulus of approximately 195.5957 kN/mm².
It was observed that HYSD bars follow a typical stress-strain behavior, with strain hardening after yielding. However, it is essential to exercise caution during testing to avoid anomalies like the one observed in sample 2, where extensometer removal timing affected the results.
These material properties are vital for structural design and quality control in construction projects, enabling engineers and managers to make informed decisions about the suitability of HYSD bars for specific applications. Precise testing procedures and instrument handling are critical to obtaining reliable and accurate results.