Measuring the Creep of Lead

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3B4 Mechanical Engineering MaterialsCreep of LeadLaboratory Report




This laboratory explores the phenomenon of creep. Creep is a slow continuous deformation within a material in response to increasing time, a constant applied stress and an elevated temperature. Here in this laboratory lead is chosen as the test metal as it is shown to have poor resistance to creep and also has a relatively low melting temperature.


Engineers are interested in the creep properties and stability of materials when designing specific parts and assemblies. Creep machines such as the one used in the laboratory are used by Engineers to determine these material properties.

Creep causes many problems to the Engineer in design. They need to determine that the materials they use will stay within the required creep limits for the lifetime of the component.

Creep is particularly important in the design components that need to withstand high temperatures. Creep will occur in metals at a faster rate as the temperature increases. These design considerations fall into four different applications:[1]

Displacement limited applications are where dimensions must be precise with small clearances and little error. The small clearances must be maintained at high temperatures. An example of this type of application is in the turbine rotors of jet engines.

Rupture limited applications are where precise dimensions are not particularly essential. However it is essential that fracture cannot occur to the material. An example of this is the need for high pressure steam tubes and pipes to withstand any break in their structure.

Stress relaxation limited applications are needed where the initial tension in component relaxes with time. An example of where this application occurs is in the pretensioning of cables on bridges or in the pretensioning of bolts.

Buckling limited applications of creep are needed in slender columns or panels which carry compressive loads. An example of this type of application would be in a structural steelwork that is exposed to fire.


The objective is to witness the creep properties in lead. To achieve this creep tests are performed on lead specimens. Three creep tests are carried out using three different lead specimens. The load is varied in each of the three tests and observations are made on the results.



Creep is a time dependent deformation that occurs under a constant applied load and temperature. The rate of creep is influenced by temperature and creep generally occurs at a high temperature. Creep then is a function of stress, time and temperature.

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The lowest temperature at which creep can occur in a given material is generally

, where Tm is the melting temperature of the material in degrees Kelvin.

Total engineering creep strain can be expressed by the following formula:

Where ε is the theoretical stress,

 is the change in the materials length and

is the materials original length.

The strain rate describes the rate of change in the strain of a material with respect to time.


 is the strain rate; ...

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