Tensile test. This test allows us to measure the ductility of the steel excavator.
For this test we need to again extract a long piece of the steel excavator shovel bucket and use the method shown below and the percent elongation and reduction area are calculated on the next page.
These 2 equations are used as indicators of ductility, i.e. the ability of the steel to be elongated in tension. As the elongation is not constant over the entire length and is greatest at the centre of the neck, therefore the percent elongation is not the complete measure of ductility. Nevertheless that is why we have the reduction of area being measured at the minimum diameter of the neck as this is an improved sign of ductility.
The creep test. This test allows us to measure the steel excavator.
To establish the creep test of the steel excavator bucket, the bucket is subjected to long-lasting steady tension and compression loading at constant temperature. Deformation is recorded at specific time intervals and a creep against time graph is plotted. We should achieve a slope and that slope of curve at any point is creep rate which is the time rate of deformation of the bucket to stress at a steady temperature. If failure occurs, it concludes the test and the time for the break of the steel bucket is recorded. If the steel bucket does not fracture within the test period, creep recovery which in turn is, the rate of decrease in deformation that occurs when load is removed, may be measured.
b) A wooden scaffold plank
For the wooden plank the three most important mechanical properties are the plank stiffness, ductility and toughness. Stiffness describes a length of planks resistance to deflection under load and modulus of elasticity in static bending can be measured. Ductility as mentioned earlier is a measure of the ability of a material to undergo plastic deformation without breaking. Finally toughness on the other hand is the resistance to fracture of a material when stressed. It is defined as the amount of energy that a material (in this case the wooden scaffold plank) can absorb before breaking. Finally ductility is a measure of the ability of a material to undergo plastic deformation without breaking.
Test procedures for the 3 properties stated
The three-point bending test. The stiffness of the planks can be measured by this method.
The diagram shown below shows the scaffold plank supported at each end in a horizontal posture. Then a load is applied to the plank and the diagram shows that the plank is bending under a load. The application of the load causes bending stresses, the fibres in the upper edge of the plank are resisting compression while those on the lower edge are resisting separation i.e. the lower part of the beam is experiencing tensile stress, while the upper part is experiencing compressive stress and there is shear stress around a neutral axis where length doesn't change, but the axis moves lower as the load increases. The wooden scaffold plank is stronger in tension than in compression so the top of the plank will fail initially if the load is increased past the plank's ultimate tensile strength. The deflection in the middle of the beam is measured to calculate the stiffness and also the modulus of elasticity can be determined by using the equation stated on the next page.
Tensile test. This test allows us to measure the ductility of the steel excavator.
The test procedure is the same as the test procedure mentioned for the steel excavator shovel bucket however we replace the steel excavator with the wooden scaffold plank.
The Charpy Test. This test allows us to measure the toughness of the wooden plank.
The Charpy test involves striking the wooden scaffold plank with a striker, usually a hammer. The plank is fixed in place at both ends and the striker impacts the wooden plank immediately behind a notch. If the specimen (wooden plank) was tough then a lot of energy would be absorbed. However this test is carried out until the wooden plank fractures.
Tensile test. This test allows us to measure the ductility of the steel excavator.
The test procedure is the same as the test procedure mentioned for the steel excavator shovel bucket however we replace the steel excavator with the wooden scaffold plank.
The Charpy Test. This test allows us to measure the toughness of the wooden plank.
The Charpy test involves striking the wooden scaffold plank with a striker, usually a hammer. The plank is fixed in place at both ends and the striker impacts the wooden plank immediately behind a notch. If the specimen (wooden plank) was tough then a lot of energy would be absorbed. However this test is carried out until the wooden plank fractures.
c) A concrete stairway in a warehouse
For a concrete stairway the three most important mechanical properties are its compressive strength, fatigue and creep. Compressive strength is the ability of a material such as concrete to resist axially directed pushing forces. When the limit of compressive strength is attained, materials are broken. Fatigue alternatively is the process of permanent structural damage occurring in a material subjected to surroundings that produce variable stresses and strains at some points and that may end in cracks or complete fracture after an ample number of fluctuations. Mechanical properties of creep are mentioned whilst analysing the steel excavator shovel bucket.
Test procedures for the 3 properties stated above
The compression test. This is used to measure the compressive strength of the concrete stairway.
A compression test determines behaviour of the concrete under severe loads. The concrete specimen is compressed and deformation at various loads and this is noted. Compressive stress and strain are calculated and plotted against a stress-strain graph which in turn will be used to find the following: elastic limit, proportional limit, yield point, yield strength and compressive strength for the concrete.
Fatigue testing. This is used to measure the fatigue of the concrete stairway.
The procedure is by a specified mean load and an alternating load is applied to the concrete specimen and the number of cycles required to produce failure is noted. The test is repeated with the same concrete however varying the loads. Loads may be applied by rotation. Data from this test are often presented in an S-N diagram which is a plot of the number of cycles required to cause failure in the concrete
(Y-axis) against the amplitude of the recurring stresses (x-axis).
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The creep test. This test allows us to measure the concretes creep.
The test procedure is the same as the test procedure mentioned for the steel excavator shovel bucket however we replace the steel excavator with the concrete specimen.
