Laboratory Report on Compression Testing A sample of polymer, in a compression test, was tested for compressive strength and stiffness. The study was conducted with a Compression method from “BlueHill 3 tensile test program” at a test speed of 1.3mm/min and a limit of strain of 0.3mm/mm in accordance with ASTM Standard D695-96. Data was collected while carrying out this experiment calculating for material properties. The compressive modulus was calculated as 21.27 whereas ultimate compressive strength recorded 8.68MPa. Value of ultimate compressive strength depicted proximity to similar value for silicon fume mortar at 9.62MPa thus the likely identity of test sample.
Properties of various engineering materials in construction determine life of structures as they influence their ability to service for long periods before failure. Failure of structures can be through collapse or reduction in serviceability as well as durability (Ward & Sweeney, 20-25). Economically, collapse of structures leads to loss of funds by stakeholders thus necessitating thorough testing to determine suitable materials for construction. Compression testing is a procedure for defining behavior exhibited by various engineering materials under loads of compressive nature.
Additionally, such tests aid in determining limits of proportionality and elasticity, points of yielding, material strength at yielding. Compressive strength and elasticity modulus are other properties that classify type of engineering materials. Ultimate compressive strength refers to the extreme pressure a material can resist prior to fracturing whereas elastic modulus refers to gradient of stress-strain curve. Brittle materials possess definite values for strength while strength of ductile materials relies on extent of alteration during testing.
This test serves to identify type of polymer sample through testing of material properties.
Stress = Load (N)/Area of cross-section (mm2)
Compressive modulus = slope of linear portion of stress-strain curve
Strain = extension/ original length
Length reduction (%) = (initial length-original length) %/ original length
Materials and Methods
1. Dimensions of sample were measured twice are different points to obtain average length (height) and average diameter.
2. Compression method from “BlueHill 3 tensile test program” was utilized in this experiment labeling test sample as “Compressio_SEC#[email protected]
” for each section number (SEC#) and sample number ([email protected]
3. Dimensional properties of sample were fed into the program.
4. The specimen was uprightly placed on the lowest salver of compressive machine.
5. Under instructions, test speeds of 1.3 mm/min and strain limits of 0.3 mm/min were set.
6. Soft keys were used to reset extension before loading.
7. Crossheads were lowered until loading meters registered a 10 N pre-load.
8. The extension was reset before loading again; repeating the process until failure of load.
Analysis of material properties utilizes formula for calculating strain, stress and Compressive modulus stated earlier. Material properties matching values recorded literature identify type of sample polymer.
Original height of specimen = 15.49mm
Final height of specimen = 15mm
% reduction in length = 30%
Diameter of specimen = 13.84mm
Compressive modulus = 21.27
Yield strength = 0.265 MPa
Ultimate compressive strength = 8.68 MPa
Figure 1: A graph of stress versus strain for test sample
The value of ultimate compressive strength for sample specimen compares with values for silica fume mortar (by-product of alloys of ferrosilicon) which yields 9.62MPa surpassing mortar strength of 8.68MPa (Ward & Sweeney, 11-14). Analysis of material properties utilizes specifications for determining strength and ductility.
Materials exhibit unique stiffness and compressive strength typical to their respective properties. In this experiment, properties of materials were investigated with a vision of identifying types of sample polymers. Civil engineers work closely with chemical engineers to manufacture polymers with beneficial properties for design practices. These polymers possess both high compressive strengths and modulus-weight ratios. The specimen recorded yield strength of 0.265MPa and ultimate strength of 8.68MPa thereby portraying ductility. Additionally, specimen reduced by 30% of its original length whereas compressive modulus was 21.27.
Results obtained in this experiment depict compressive strength and stiffness of sample polymer. The probable source of experimental error lies in safety stop prior to determining ultimate compressive strength. Owing to errors in timing safety stops, actual value of ultimate compressive strength may be unattainable.
The sample tested in this study exhibited statistically momentous stiffness and compressive strength typical of silica fume mortar.
Ward, I. M., & Sweeney, J. (2012). Mechanical properties of solid polymers.