Material Properties - Lab Report Example

Running head: Title of Work Name Name of instructor Subject Institution Date Experiment 1 Introduction Engineering materials have different mechanical properties. Hooke’s law tries to examine the characteristic properties by means of drawn graph, where different material exhibit similar characteristics. This study is important as in enables the right choice of material, to be used for a given specific purpose. (Hibbeler, pp132-133)When materials are subjected to some forces say, tensile or compressive, their mechanical properties are altered. Most materials obey the Hooke’s law while others do not. This paper tries to stipulate the validness of a plastic material if it obeys hooks law. Experiment method Various apparatus are used such as; weighing scale, ruler, weights, scissors for cutting the strip, a clamp for holding the experiment. Masses from 100g are attached to the strip of plastic which is of width of about 45mm.The strip are of varied length and of different materials such as styrene and polystyrene. Whenever a mass is attached, the length of the strip is measured. This is repeated with other masses of same magnitude say 200g.The length is recorded again. This is done till the piece of plastic strip snaps. Sample results data for the experiment. Load(N) Extension(mm) 10 0.02 50 0.03 100 0.05 200 0.06 300 0.07 400 1.00 500 1.1 700 1.5 800 2.0 855 2.5 700 1.5 Results Discussions Longer strips take long time before it gets snap. This is due to the more rearrangement of molecules within its structure. The shorter strip snaps earlier as seen. The trend of the curves is seen to take a certain shape which actuates the hooks law. Materials made from polystyrene seem to disobey hooks law due to their molecular structure arrangement. Conclusions Most of the plastic type material obeyed the hooks law where the elongate up to a certain limit known as yield point before they undergo a point that is beyond plastic deformation. The errors that may have occurred are due to systematic effects such as, environmental condition that causes the material to either expend or contract. Also effects due to vibration and parallax reading could result to wrong results. Experiment 2 To subject beams of different materials to varying loads and measuring the deflections of the beams along their length. Introduction Beams are structural members that assist in engineering purposes such as airplane, building purposes, bridges and even in airplanes. The beams would usually give support to the transverse loads. (Hibbeler, pp200-203) The determination of the deflection point of the beams is of great importance as it would enable an Engineer know where to attach the support while constructing any structure. In addition, different materials have different characteristic properties hence there is the need to determine their deflection points to ascertain the areas where there is possibility of occurrence of maximum stresses. Objectives The objective of this experiment is to determine the deflection curves of different engineering materials that are used in application and analyze them graphically. This would be able to indicate the maximum forces that can be applied to a given member. This study also enables one to understand the integration of individual stresses at the deflection points that may cause the failure of a given material. Also, the relationship between the deflection of a member due to its weight and its load may be determined. Experimental method Various apparatus are used during the experiment. Frames of different materials with rollers, hanger and weights .The vernier caliper finds its application in the measuring the depth and width of the beam. A dial gauge would measure the deflection along a given member. The tape measure would be used for measuring the distance between two given support. Two specimens are selected so as to carry out the experiment. They are supposed to be from different materials. A test rig is installed on the beams depending on the end choice .The beam deflection ( is then measured at given points say. After that, a load of say  is applied at the central point of the beam. The deflection ( is measured again atdifferent points along the beam. Repeat the same procedure with other loads in an equal range, then measure the deflection points. Results Discussions The nature of deflection of a beam yields an elastic curve that can be determined. As it can be seen the deflection are normally small that’s why it is difficult to note the original length of the beam with the original length. Moreover, the elastic curve presumes a flat shape due to negligible slope that is obtained. To get the slope this equation becomes handy;  Due to the small nature the value o f = The different variations of the length may be stipulated as  Given =curvature radius at a given arc length. The negligible deflection makes the elastic curve to be flat hence the arc length is almost equal to. These results to Substituting yield to Given a homogenous material the application of Hooke’s law may be stipulated as . The flexure formula gives,  The relationship yields  M is internal moment of the beam E the modulus of the material I –which is second moment of area of beam. The deflection of the beam would results to  Experiment 3 Introduction At times the use of mathematical techniques becomes cumbersome in determining the stress distribution. This may be solved by use of a polarized light where even points of discontinuities may be noted. Moreover stress distribution may be deduced from even shapes that are not regular. Experimental methods The apparatus used in the experiment include, dividers, vernier calipers, and a Hounsfield tensometer. A polariscope aids in the measuring of the photo elastic effect. A ray is passed on materials which is photoelectric. Initially light is passed into a polarizer that changes the light to a plane which is polarized. The light is split along the directional stress areas. (Hibbeler, pp189-192) A refractive index is generated in each of the e material under test. The stress optic law is applied in determining the stress distribution. Results Sample image of pattern of stresses Discussion The stress optic law is given by  where R=the retardation induced C=the co-efficient of the stress T=thickness Fringe patterns are created which helps in the determination of stress determination. The stresses may appear at isoclinics which are the loci that the principle stresses occur in the same direction. The stress concentration factor occurs to the area where the load is not evenly distributed. Conclusion Generally, the use of pho elastic may be used to determine the stress concentration factor and, assists engineers to know the distribution of forces in a given area. References Hibbler, R.C. (2005) Mechanics of materials. U.S.A: Pearson prentice Hills.pp127-205 Risk assessment. Hazard Control Remedial Traps from moving objects Make use of gang ways Warning signs may be installed Open apparatus Apparatus should be covered Safety guards may also be used Pricks resulting from sharp objects Be cautious of the environment May use leather gloves. Effect from bright light Take experiment in a dark area May put warning signs and protective shields. Read More