Matthew DeMasiAndrew ChapmanENME E3114 Spring 2015Experiment Date: March 5, 2015Experiment 1: Material Properties in Tension and Compression

Objective:The purpose of this lab was to test and observe the failure mechanisms of different specimens under tension and compression. Specimens of A36 steel, cast iron, rubber, wood, and concrete were loaded under tension and compression to observe the material properties such as yield strength, ultimate strength, and ductility.Apparatus, Specimen and Testing Conditions:Apparatus: INSTRON 600DX This machine has a maximum capacity of 135 kip in tension and compression. The machine was used to test the tension of the A36 steel, the cast iron, and the ash wood specimens; it also was used to test the compression of the ash wood and concrete specimens. It has capabilities of load and displacement control, and has a controller system to display load and strain values. INSTRON 1500 HDX This machine has a maximum capacity of 300 kip in tension and compression. This machine was used to test tension and compression of the concrete. It has capabilities of load and displacement control. Crane Apparatus The crane apparatus held a connection so that the rubber sheets could hang vertically from one end. Extensometer Compressometer The extensometer is an LVDT to measure the vertical displacement on the concrete cylinder. The compressometer is an LVDT to measure the horizontal displacement on the concrete cylinder. 2 inch extensometer Limited to 10%; 0.2 in seen after sufficient plastic deformation. Caliper Tape Measure Weights of 5 lbs and 10 lbs.Specimens: A36 Steel (Tension) Diameter = 0.504 in; Gauge Length = 2 in Cast Iron (Tension) Diameter =0.0505 in; Gauge Length = 2in Ash Wood (Tension) Cross Section: Height = 0.372 in, width = 0.197 in; Length = 1.9875 in Ash Wood (Compression) Cross Section: height = 1.879 in; width = 1.989 in; Length = 7.9375 in Concrete (Axial Compression and Compression along diameter) Diameter = 4 in; Height = 8 in Three Rubber Sheets Uniform Sheet Grid Size: Cross Section: Height = 1.085 in, Width = 1.026 in; Thickness = 0.258 in Sheet with Notches Grid Size: Cross Section: Height = 1.263 in, Width = 1.274 in; Thickness = 0.248 in Sheet with Hole Grid Size: Cross Section: Height = 1.001 in, Width = 0.999 in; Thickness = 0.252 inConditions: Concrete was made in January, so that curing for a minimum of 27 days was achieved. For the compression testing on the ash wood, there was a knot on the outer face.Procedures:A. Steel1. Measure the cross sectional dimensions and length of the A36 steel between gage points. 2. Load the specimen in tension on the INSTRON 600DX. At yielding, remove the extensometer once it reaches its limit (10%). Measure the deformed cross section and gage length.3. Continue loading the specimen until failure. At every 0.1 inch increase in length, measure the cross section and length of the specimen. At failure, measure the final length of the specimen.4. Measure the cross sectional dimensions and length of the Cast iron specimen. Load on the INSTRON 600DX until failure and then measure its cross section and length.B. Wood1. Measure the cross section and length of the tensile wood specimen. Load on the INSTRON 600DX until failure.2. Measure the cross section and length of the compressive wood specimen. Load on the INSTRON 600DX until failure.C. Concrete1. Measure the cross section and length of the concrete specimens.2. With the extensometer compressometer attached to the concrete specimen, load to 50,000 lbs on the INSTRON 600DX. 3. Transfer to the INSTRON 1500 HDX until failure and record the load.4. Place a specimen along its diameter on the INSTRON 1500 HDX and load until failure.D. Rubber1. Measure the initial grid size of the uniform rubber sheet. Attach the sheet to the crane apparatus, and load in increments of 5 lbs until 50 lbs is reached. For each load, measure the deformed grid size. Repeat procedure for the rubber sheet with notches and the rubber sheet with the hole.

Figure 1: Concrete under compressionFigure 2: Necking of A36 steel under tension.

Data Analysis & Discussion of Results:Figure 3: Engineering Stress Strain Curve (-x) of the uniform rubber sheet.

Figure 4: Engineering Stress Strain Curve (-y) of the uniform rubber sheet.

The stress was calculated by and the strain was calculated by . As shown in Figures 3 and 4, as the stress is increased, the strain increases in the y direction and decreases in the x direction. This was shown in the experiment as when more load was applied (an increase in stress), the length of the sheet increased (y-strain increases). As the vertical length increases, the horizontal section of the rubber sheet decreases (x-strain decreases). The curves are not linear though because there are unequal increases or decreases in strain for corresponding increases in stress. There may be significant error in the use of the caliper as the small deformations could lead to skewed results; repeating measurements often produced vastly different results due to the small size of deformations. Thus, these calculations are inaccurate due to lack of precise testing.Figure 5: Poissons Ratio-Stress Curve (-) of the uniform Rubber Sheet.

Poissons Ratio was calculated by: . When plotted against the stress, the Poissons Ratio steadily decreased with an increases in stress for low stress values. However, the graph linearity ends with a horizontal line and a slight increase. This is most likely an indication of an error in the experiment; as discussed, the slightest of movements of the caliper produced very large discrepancies in value which most likely skewed the result.

Figure 6: Engineering Stress Strain Curve (-y) of the uniform rubber sheet, notched rubber sheet, and rubber sheet with hole.

The hole and notch produced an overall flatter stress strain curve than that of the uniform specimen. For the same stress, the hole deformed the greatest (strain), and the uniform sheet deformed the least. Thus, the holes and notches deformed more easily than that of the uniform sheet.Figure 7: Engineering Stress Strain Curve of the A36 Steel Specimen.

The A36 steel specimen was loaded in tension on the INSTRON 600 DX, which recorded the load and strain. The stress was calculated by:

in which P was the load, and A was the initial area. As seen in the graph, the stress-strain relationship is elastic until the yield point is reached (at the sharp tip at the end of the elastic region). At this point, plastic deformation begins as the material starts to yield in the horizontal line region. The graph then curved upwards during strain hardening in which an increase in load can be supported by the specimen. This curve rises continuously but become flatter until the ultimate stress (the highest point in the graph) is reached. The graph then curves downward until fracture.

Table 1: A comparison of the experimental and accepted values of A36 steel under tension.Experimental ValuesAccepted Reference Values

Yield Strength (psi)51,667Minimum 36,000

Youngs Modulus, E (psi)29,306,53629,000,000

Ultimate Strength (psi)65,47358,000-80,000

The yield strength is the point on the stress-strain graph (Figure 7) in which yielding starts. At this point, the specimen will continue to elongate without any increase in load; it is in a perfectly plastic state. This is seen in the horizontal line as there is an increase in strain without an increase in stress. The experimentally calculated yield strength meets the requirement to be over the accepted minimum of 36 ksi. The Youngs Modulus for A36 steel is 29000 ksi; the experimentally determined value, from the slope of the stress-strain elastic region, is extremely close to the accepted value. The ultimate strength is the maximum stress supported by the material; it is the highest point on the graph. The determined value falls within the range of accepted values of 58-80 ksi.

Figure 8: A comparison of the true stress-strain and engineering stress-strain curves of A36 steel.

The true stress was determined from in which A is the deformed area. The true strain is calculated from =ln(L/L0)=ln(1+). Due to necking, the true stress is greater than the engineering stress towards fracture, but is similar to the engineering stress in the elastic range. This is seen in Figure 8 as the curves are nearly identical in the elastic range, but true stress is greater than the engineering stress for points beyond the elastic range.The A36 material displayed ductile behavior; ductile materials are capable of absorbing large amount of energy and will exhibit large deformation before failing. This is seen by the elastic stress-strain behavior, yielding at constant stress, strain hardening, and failure by necking. There is a large deformation during yielding and strain hardening before the failure occurs.The fracture surface is indicative of a ductile material. During elongation, the deformation is uniform over the length as the cross sectional area decreases up to the ultimate stress. However, right before failure, the specimen displayed necking in a localized region of the specimen. This neck forms as the specimen elongates further until it fractures right at this neck in the center.

Table 2: The ultimate strength of cast iron under tension.Ultimate Strength (psi)39222

The cast iron displayed brittle behavior, indicated by a lack of a well defined fracture stress or a yield point. There is very little yielding because once past the elastic region, the specimen will fracture completely without necking. This is a uniform deformation throughout the length until failure. The fracture surface occurred at the cross section without necking; the cross section of the fracture was thus the same as the cross section at a point without fracture. It failed more toward the joint of the specimen; this could be an indication of a microscopic crack at that point that quickly spread across the specimen.

The Stress strain curve for the concrete cylinder under compression is shown in Figure 8 below.

Figure 8: Stress-strain curve for concrete cylinder under compression

The ultimate strength, fc, was determined to be 4056 psi. The youngs modulus, E, was determined to be 6635. Poissons Ratio was calculated by: . The Poissons Ratio was plotted against the stress as shown in Figure 9.

Figure 9: Poissons ratio vs. stress for concrete cylinder under compression

The concrete cylinder in tension supported a maximum load of 18,037 lbs when force was applied to its side (non-axial compression). The equivalent tensile strength was then computed using the formula: . This yielded a tensile strength of 359 lbs. The manner in which the concrete cylinders failed was dramatically different depending on whether compression or tension was applied. The cylinder in compression exhibited a pyramid-like failure, where the upper portion of the cylinder ended up being shaped like an inverted cone (Figure 10). The cylinder in tension failed along the cylinders diameter line all along the axis (Figure 11).Figure 10: Concrete compression failureFigure 11: Concrete tension failureThe ash wood in tension had a minimum cross section of 0.0737in2 and failed at a max load of 804lbs. This gives a maximum strength of 10912psi in tension. The ash wood in compression had a cross section of 3.606 and failed at a max load of 37455lbs, giving a maximum strength of 10387psi in compression. The wood samples were unique from the metal, concrete, and rubber samples in that they had pronounced grains. When the wood samples failed, they failed along their grains. However, the failures of the ash wood samples in tension and compression did show some marked differences. The wood in compression failed in a clean break along the grain, while the fibers in tension were ripped apart, making for a much more jagged failure.

Conclusions: Experimentally determined generally fell within theoretical ranges for the steel, wood, concrete, and rubber tests. The inconsistency of the Poissons ratio vs stress diagram for the uniform rubber sheet indicates the presence of potential errors. A potential source of error in the rubber tests was in the accuracy of measurements. As weight was added, some of the dimensions changed in ways antithetical to expectations. A potential source of error in the compression tests for both wood and concrete was that the samples may not have been loaded completely vertically. Any deviation off of the vertical would have given inaccurate strengths for the materials.