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Creep testing machines

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Creep testing machines

  1. 1. Creep Testing Machines Group / A- Ibrahim Ahmed Ibrahim B- Ahmed Alam Elsaid C- Ahmed Hassan Abd Elaaty D- Maged Abd Elmon`m Korany E- Mahmoud Mohammed Abd allah F- Wael Garib Mostafa Under Supervision Of / Dr / Sabbah Ataya
  2. 2. What Creep Mean? <ul><li>The time dependent deformation under constant load at high </li></ul><ul><li>temperatures is called creep and the resulting strain is a function of the applied stress, temperature, and time. </li></ul><ul><li>It is found that creep in metals starts when the temperature is > 0.3 to 0.4 T m.. </li></ul><ul><li>Creep is important in design in industry in three types of high temperature applications: </li></ul><ul><li>1- Displacement-limited applications in which precise dimensions or small clearances must be maintained such as in turbine rotors in jet engines) (Figure 1a). </li></ul>
  3. 3. <ul><li>2-Rupture-limited applications in which precise dimensions are not essential but fracture must be avoided such as in high-pressure steam tubes fig (1-b). 3- Stress-relaxation-limited applications in which an initial tension relaxes with time such as in suspended cables and tightened bolts (1c) </li></ul><ul><li>Creep test </li></ul><ul><li>The main objective in a creep test is to measure how a given metal or an alloy will perform under constant load, at elevated temperatures. In a creep test, a tensile specimen (with similar dimensions as a tensile test specimen) is subjected to a constant load inside a furnace where the temperature is maintained constant. </li></ul>Tensile test specimen
  4. 4. <ul><li>These machine has a choice of load capacities: 50, 30, 20 and 10 kN. </li></ul><ul><li>The DMG TC machine has four chromium plated steel columns and substantial upper and lower crossheads. </li></ul><ul><li>The load frame is supported by a completely enclosed robust base unit which has four corner levelling feet and a protective formica top cover. </li></ul><ul><li>The upper crosshead carries the lever </li></ul><ul><li>assembly which includes a lockable </li></ul><ul><li>counterbalance weight. There are hardened </li></ul><ul><li>knife-edges at all fulcrums. </li></ul>
  5. 6. <ul><li>When the furnace is raised there is complete accessibility for specimen replacement and extensometer/thermocouple attachment. The furnace can be supported in any position by </li></ul><ul><li>a lockable clamp. </li></ul><ul><li>The correct load is applied to the specimen when the lever is in the horizontal position. To reposition the lever manually, the loading string can be raised or lowered by rotating the chromium plated capstan handwheel at the rear of the base unit. Through a 20:1 ratio worm gearbox and drive shaft, the lead screw connected to the lower loading bar can be adjusted up to its full travel of 100 mm. </li></ul><ul><li>TEMPERATURE CONTROL </li></ul><ul><li>Temperature is controlled directly from a thermocouple on the test specimen. The three-zone controllers incorporate the Eurotherm 800 Series microprocessor based instruments which give three-term control and digital display. </li></ul><ul><li>Figure 3 shows a schematic creep curve for a metal tested at constant load until rupture. Metals, polymers, and ceramics all show similar strain-time behaviors. </li></ul>
  6. 7. <ul><li>1.Primary creep where the rate of change of strain </li></ul><ul><li>(creep rate=∆ε/∆t) decreases with time due to strain hardening of the material. </li></ul><ul><li>2. Steady-State creep where the strain increases linearly with time. From design point of view, this region is the most important one for parts designed for long service life because it comprises the longest creep duration. The main creep test result is the slope of this region which is known as the </li></ul><ul><li>steady-state creep rate ( ′ ε ). During this stage of creep, there is a balance between strain hardening due to deformation and softening due to recovery processes similar to those occurring during the annealing of metals at elevated temperature. </li></ul><ul><li>3. Tertiary-creep where the strain increases rapidly until failure or rupture. The time to failure is often </li></ul><ul><li>called the time to rupture or rupture lifetime </li></ul><ul><li>(T m ). </li></ul>

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