mechanical properties of materials

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May 15, 2015 Danial Naeem Umer Farooq Nouman Butt Shahzad Shabbir Ayesha Saddiqa Mechanical Properties of Materials

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May 15, 2015Danial NaeemUmer FarooqNouman ButtShahzad ShabbirAyesha SaddiqaMechanical Properties of MaterialsSample PreparationResults/ApplicationsAdvantages/DisadvantagesVickers Micro Hardness TesterIntroduction/HistoryPrincipleConstructionWorkingContentsUniversal Testing Machine

Introduction/History Principle/Working Construction Sample Preparation

Results/ApplicationsAdvantages/DisadvantagesWhat are the mechanical properties of a material?The mechanical properties of a material are those properties that involve a reaction to an applied load.The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected.Mechanical properties are also used to help classify and identify material.The most common properties considered are tensile strength, ductility and hardness etc.How Hardness is defined?Hardness is a resistance to deformation or indentation. Property of the material that enable it to resist plastic deformation.Vickers Micro Hardness TesterIt works on the technique of Indentation Hardness

The first Vickers Micro Hardness Tester was developed in1936

ConstructionSquare based diamond pyramid indenter with 136 degrees between opposite faces

Lower magnification lens 10XHigher magnification lens 40X

Working

The Vickers Hardness Number is defined as the load divided by the surface area of the indentation

VHN= 1.854P/L^2Sample Preparation Metallographically Polished and mountedSizeThe smaller the part, the lighter the load required to produce the required indentation. Minimum thickness and proper indentation required for small parts. Larger parts need to be fixtured properly.Parts should be clamped into place on the anvil.Surface of the specimen should be smooth (for good measurement).

Thickness of a sample

Sample should have a minimal thickness that is at least 10x (ten times) the indentation depth that is expected to be attained.

Sample shoud be about 1 in. (25 mm) by 1 in. (25 mm) by 1/2 in. (12 mm) thick.

Cylindrical samples

A correction is needed to the test due to a difference between axial and radial material flow.It is important to maintain a minimum spacing equal to 2~1/2 times the indentation's diameter from an edge or another indentation.

Sample should be perpendicular to the indenter. The indentations should be as large as possible to maximize the measurement resolutionThin, flat samples, such as sheet material, can be tested without mounting or preparation if the surface finish is suitable.

Opposing indenter faces are set at a 136 degree angle from one another.

ApplicationsThe hardness tester is used in most laboratories for the testing of metal specimens and the hardness distribution of hardened and carburized surface.It is suitable for testing small parts, thin plates, metal foils, electroplated layers, and non-metallic materials.The test is accurate and reliableProvide precise and detailed information on surface features of materials that have a fine microstructure, are multi-phase, non-homogeneous.Determine hardness of different micro-constituents within a structure.

Advantages Can be used for soft metals such as... Elastomersthermoplastic elastomers vulcanized rubber And hard metals as well... Tin Aluminium Gold Copper Iron Tests may be conducted in low-load and micro range as well.It does not have a number of scales and indenters.Limitations

The main disadvantage is the need to optically measure the indent size.Slow, testing can take 30 seconds, not counting the preparation time.Universal Testing Machine15A universal testing machine (UTM) ,also known as universal tester.

It is used to test the tensile strength and compressive strength of materials.

It is named after the fact that it can perform many standard tensile and compression tests on materials, components and structures.Introduction

MechanicalThe electromechanical machine uses the electric motor, gear reduction system and one, two or four screws to move the crosshead up or down

A range of crosshead speeds can be achieved by changing the speed of motor.HydraulicA hydraulic testing machine uses either single or dual acting piston to move the crosshead up or down.

In a manually operated machine , the operator adjusts a needle to control the rate of loading. In a close-loop hydraulic servo system, the needle valve is replaced by an electrically operated valve servo for precise control. TypesDigitally operated universal testing machine

Computer operated universal testing machine

Single column universal testing machine

Double column universal testing machine

Four column universal testing machine TypesConstruction of Universal Testing Machine

Testing machine was designed to determine the stress strain curve of thin materials such as polymers and particularly metallic films deposited onto polymeric substrates.The mechanical design minimizes effects of load introduction in the main frame, drive screws and the relative movement between the movable cross head and drive screws. Testing machine is composed of five main parts:

The testing machine is mainly made of stainless steel, excepting some frictional elements like the gears, which were made of bronze.The main frame includes the rectangular base where the gearbox is placed, the fixed crosshead and two vertical parallel columns.The drive system includes a stepper motor with variable speed. The gearbox is formed by a worm shaft, and two worm gears, which moves the two drive screws.

The moveable crosshead is integrated by the bottom grip, two conical fastener tools with internal thread and an adjustable conical ring.The conical fastener tools provide stabilization to the moveable crosshead when moving along the drive screws.The load cell can be used for tension and compression testing, it is located on the upper side of the frame and supports the upper grip.

22The digital indicator measures the crosshead displacement and consists of a digital micrometer from starret with 0.001 mm of resolution, which is connected to a personal computer to acquire data.To achieve high resolution in the measurements, the device includes a stepper motor used to control both velocity and torque.Two stainless steel grips ( one fixed to the load cell and the other on the moveable crosshead ) are used to hold the sample. The grips were designed with smooth surfaces to avoid damage to soft and thin samples.

Each grip is composed by a fixed part and a moveable plate joined with two screws to uniformly press the sample.This holding system avoids sliding between sample and grips during tensile test.The design of this universal testing machine permits the interchange of the different parts such as the load cell , grips and drive screws in order to extend the user requirements.Stress strain data are captured and saved in a data file through a GPIB interface controlled with a home made protocol programmed in Labview.

Specimen for UVTA Tensile specimen is a standardized sample cross-section.It has two shoulders and a gauge in between. The shoulders are large so they can be readily gripped.The important part of specimen is the gage section. The cross-sectional area of the gage section is reduced relative to that of remainder of the specimen so that deformation and failure will be localized in this region.The gage length is the region over which measurements are made and is centered within the reduced section.

Tensile specimen made from an aluminum alloy.A standard specimen is prepared in a round or a square section along the guage length, depending on the standard use.The two left specimens have a round cross-section and threaded shoulders.The right two are flat specimen designed to be used with serrated grips.

The initial gage length is standardized (in several countries) and varies with diameter ( Do) or the cross- sectional area (Ao) of the specimen as listed Type specimenUnited stateBritainGermany Sheet 4.5 5.65 11.3 Rod 4.0 5.00 10.0It works on the principle of elongation and deformation

In UTM tensile, compressive and Shear Forces are acting

Working Principle

Compression TestA compression test is a method for determining the behavior of materials under a compressive load . Compression test are conducted by loading the test specimen between the two plates and then applying a force to the specimen by moving the crossheads together. During the test, specimen is compressed , and deformation verses the applied load is recorded. The compression test is used to determine the elastic limit ,proportional limit, yield point, yield strength, and for some compressive strength.

In compression test specimen is gripped in machine jaws and load is applied through screw gear mechanism by a moveable crosshead jaw when we apply load our specimen is compressed under load and its compressive strength shows on screen by graph.

Working Procedure

Tensile TestTensile testing is a way of determining how something will react when it is pulled apart i.e. when a force is applied to it in tension. In tensile testing a specimen is subjected to an increasing axial load while measuring the corresponding elongation until it fractures. The test is designed to give the yield stress, ultimate tensile test and percentage elongation for the materials In tensile test the specimen is gripped in machine jaws and load is applied through a screw gear mechanism by a moveable crosshead when we apply load our specimen is elongated under load and stress strain graph is obtained on screen Tensile TestUNIVERSAL TESTING MACHINEAPPLICATIONS ADVANTAGES AND DISADVANTAGES OF UTM36APPLICATIONS UTM is suitable to test various metallic and non metallic materials for tension, compression, bending and shearing strength.

It is capable of testing the character of materials on physical and technology properties.

It is easy to operate and widely used in works, laboratories for research and quality control.Applications UTM are used to conduct the following tests:

Tension test on metal, synthetic materials etc.

Compression test on springs, rubber etc.

Bending/transverse test on beams, synthetic materials.Shear test on metals, polymers.AdvantagesCost saving in the tens of thousand of dollars when compared to purchasing a new machines.

Increased capabilities, flexibility and accuracy of your materials testing system.Reduced testing times.Achieved test results to generate compressive reports.Advantages

Fast and error free calculations.

Streamlined operations and effortless training.

Increase credentials surrounding your product to support your business development efforts.

An additional advantage of our testing is the lower cost and smaller size as compare to other commercial machines.

DisadvantagesThis machine may not work with brittle materials .

That experience short elongations prior to fracturing.

Alignment of the material is critical.

If the material is misaligned the machine will exert a bending force on the material.

Disadvantagesthe initial portion will be curved and not linear which indicates the misalignment.

The result will be changed.Thank You