Polymer Process EngineeringCBB 4423

Experiment 4: Universal Testing Machine

Group Members:Ahmad Fikry b. Mohd Anwar11866Fareeda Chemat11806

Programme: Chemical EngineeringLecturer: Assoc. Prof. Dr. Zakaria bin Man

May 2012

1.0 Objective The objective of this experiment is to help student to be familiar with universal testing machine.

2.0 Theory2.1 Universal Testing MachineA universal testing machine, also known as auniversal tester, materials testing machineormaterials test frame, is used totestthetensile stressandcompressive strengthofmaterials. It is named after the fact that it can perform many standard tensile and compression tests on materials, components, and structures.

Figure 1: Universal Testing Machine. Load frame - usually consisting of two strong supports for the machine. Some small machines have a single support. Load cell- Aforcetransduceror other means of measuring the load is required. Periodiccalibrationis usually called for. Cross head - A movable cross head (crosshead) is controlled to move up or down. Usually this is at a constant speed: sometimes called aconstant rate of extension(CRE) machine. Some machines can program the crosshead speed or conduct cyclical testing, testing at constant force, testing at constant deformation, etc. Electromechanical, servo-hydraulic, linear drive and resonance drive are used. Means of measuring extension or deformation- Many tests require a measure of the response of the test specimento the movement of the cross head.Extensometersare sometimes used. Output device - A means of providing the test result is needed. Some older machines have dial or digital displays andchart recorders. Many newer machines have a computer interface for analysis and printing. Conditioning - Many tests require controlled conditioning (temperature, humidity, pressure, etc.). The machine can be in a controlled room or a specialenvironmental chambercan be placed around the test specimen for the test. Test fixtures, specimen holding jaws, and related sample making equipment are called for in manytest methods.

Figure 2: Schematic diagram of a tensile test2.2 Stress Strain CurveThe relationship between thestressandstrainthat a particular material displays is known as that material's stress-strain curve. It is unique for each material and is found by recording the amount of deformation (strain) at distinct intervals of tensile or compressive loading (stress). These curves reveal many of the properties of a material (including data to establish the Modulus of Elasticity, E). Stress-strain curves of various materials vary widely, and different tensile tests conducted on the same material yield different results, depending upon the temperature of the specimen and the speed of the loading. It is possible, however, to distinguish some common characteristics among the stress-strain curves of various groups of materials and, on this basis, to divide materials into two broad categories; namely, the ductile materials and the brittle materials.

Figure 3: Stress strain curve showing typical behavior for nonferrous alloys. Stress () is shown as a function of strain ().1: True elastic limit2: Proportionality limit3: Elastic limit4: Offset yield strength2.3 Tensile StrengthTensile strength is the stress at which a material fails (breaks) under tension. It defers from yield strength because the latter is the stress where the elastic limit of the material is reached or in other words the deformation when additional force is applied is no longer proportional to the force and the length of the material will no longer return back to its original length when the force is removed.For a material subjected to pure axial tension, the breaking strength is equal to the force applied to cause the failure divided by the smallest cross-sectional area of the material. This is normally expresses as: = F/AWhere; = the breaking strength (stress)F = the force applied that caused the failureA = the least cross- sectional area of the material Materials subjected to bending also incur tension stress on one side and compression on the other side.The units of stress are the same as those of pressure.We will use pascals, Pa, as the units for the stress. In the polymer literature, stress often is expressed in terms of psi (pounds per square inch).

2.4 StrainThe strain is a measure of the change in length of the sample. The strain commonly is expressed in one or two ways.elongation:

Where;

L= the final lengthL0 = the original length

extension ratio:

The strain is a unitless number.

2.5 Youngs ModulusYoungs modulus is the ratio of stress to strain. It also is called the modulus of elasticity or the tensile modulus.Youngs modulus is the slope of a stress strain curve. Stress strain curve often are not straight line plots, indicating that the modulus is changing with the amount strain. In this case the initial slope usually is used as the modulus, as is illustrated in the diagram at the right.Rigid materials, such as metals, have a high Young's modulus. In general, fibers have high Young's modulus values, elastomers have low values, and plastics lie somewhere in between.

Young's modulus,E, can be calculated by dividing thetensile stressby thetensile strainin the elastic (initial, linear) portion of thestress-strain curve:

Where;Eis the Young's modulus (modulus of elasticity)Fis the force exerted on an object under tensionA0is the original cross-sectional area through which the force is appliedLis the amount by which the length of the object changesL0is the original length of the object.3.0 Procedure1. Switch ON power system.2. Press safe line yellow button until light off.3. Machine will starting up and at machine controller keyboard press A button to establish open access. 4. Select B for remote control program.5. Start up the computer system and select NEXYGEN software, after that select Lr Lrx Console.6. Display monitor at machine controller keyboard must display Under control of remote computer. From now the gripper frame can control from computer (console).7. From Nexygen program, go to EDIT, select Insert New Test and select sample type (plastics, rubber, metals or etc.).8. Select either Compression Setup or Tensile Setup.9. Fill in the dimension or specification of the sample.10. Insert the specimen ( PE, PP, composite) to gripper frame.11. Select zero 0 for zeroing the Load and Stroke. Start the test by select the Start Test.12. The machine now under running condition and will stop automatically after fracture detected.13. Switch off POWER and DO the CLEANING PROCESS.

Referenceshttp://en.wikipedia.org/wiki/Young's_modulushttp://faculty.uscupstate.edu/llever/Polymer%20Resources/Mechanical.htm#elongationhttp://faculty.uscupstate.edu/llever/Polymer%20Resources/StressStrain.htm#Strainhttp://answers.yahoo.com/question/index?qid=20080724124155AALshMS