Temperature Controlled Testing of Materials

ndustries as diverse as aerospace, automotive, food, beverage, pharmaceutical, power, oil and gas and many more have a common requirement: that materials used in processes and manufacturing can experience a range of temperatures.

Materials testing is a well-established technique for measuring tensile strength, compression, flexure, friction, tear, peel, adhesion, shear, ductility, insertion, shear strength and many other parameters. In most laboratories, these tests are carried out at ambient temperature.

It makes sense however to be able to test materials at the temperature at which they will ultimately be used. In order to do this, it is necessary to add heating and/or cooling facilities to the materials testing machine.

Use of Thermal Cabinets on Materials Testing

The addition of a thermal cabinet to a materials testing machine allows testing of samples under pre-defined temperature conditions.

Thermal cabinets are mounted on wheels, which run on a separate base unit for forward and backward movement. When the cabinet is in the rear position it is clear of the test machine crosshead and normal ambient tests are possible. A glass observation panel in the front door allows the specimen to be inspected during heating tests.

Thermal cabinets are supplied with stand-alone precision temperature controllers and are available in heating-only and combined heating and cooling variants. Cabinets will be supplied complete with loadcell rods and a base assembly to fit the materials testing machine.

Thermal cabinet from Lloyd Instruments

Figure 1. Thermal cabinet from Lloyd Instruments

Application of High Temperature Furnaces

For some applications, 300¢ªC is insufficient, and then a high temperature furnace is required. High temperature furnaces can offer a temperature range from 50 to 950 ºC and are designed to ensure a uniform temperature over the full length of the furnace.

High temperature furnace from Lloyd Instruments

Figure 2. High temperature furnace from Lloyd Instruments

Automation of High Temeperature Furnaces

Thermal cabinets and high temperature furnaces generally have their own controllers for setting the temperature, but testing can be greatly speeded up if temperature control can be linked in to the universal testing machine's control and analysis software.

By allowing temperature values to be read and independently controlled, the system may be programmed to run heating and cooling cycles. This allows testing to be performed not only at high temperature but also at the end of a temperature conditioning cycle.

Application of Dual Furnace Configuration in the Steel Industry

A more sophisticated arrangement involves the use of two furnaces, and such a configuration has been implemented by Lloyd Instruments for use in the steel industry.

It is possible to interface two furnaces to the 100 kN LR100KPlus floor-standing twin column materials testing machine (as well as to its 150kN and 300kN models) NEXYGENPlus control and test software interfaces to a data acquisition card to allow temperature values from the furnace controller(s) to be read and independently controlled.

The system may be programmed to run any number of heating and cooling cycles as well as holding the sample at a particular temperature for specified time periods.

Once the temperature cycling process is completed, tensile tests are also performed completely automatically. The software continuously records the temperature throughout the test allowing graphs of time, load, extension, stress and strain to be plotted against temperature, to give a high level of analysis. Once the tensile tests are completed, the furnace is automatically cooled to allow loading of the next sample.

The automation of this process brings two key benefits. Firstly a huge amount of time is saved as the operator is only required to load the sample at the beginning of the test and unload it at the end. It avoids operators having to be present to adjust furnace temperatures over cycle times, which may last hours. Secondly, the automated process is carried out under identical operating conditions each time, eliminating any possible human errors in setting temperature values incorrectly or for the wrong periods of time.

The system can be fully automated using a single furnace, however by fitting two furnaces to the test machine, one furnace can be used for sample conditioning while the other is positioned for the tensile test itself.

Once the first tensile test is completed, the furnace positions are physically exchanged, allowing the next conditioned sample to be tested. In this way, sample throughput can be even further enhanced.

The LR100KPlus twin column materials testing system can be used for test applications up to 100 kN (22000 lbf). The large working test space between columns of 620 mm (24 in) provides room for the furnace to be fitted. The furnaces used in this application can generate temperatures up to 950¢ªC.

The LR100KPlus has a total crosshead displacement of 1150 mm (45.3 in) to provide accurate and consistent testing on a wide variety of materials.

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Summary on Materials Analysis

Fully automated, temperature-controlled materials analysis is possible by adding thermal heating, heating and cooling or furnaces to a software-controlled materials testing machine. However it should be noted that the versatility of the control software is such that it is not restricted to the automation of heating and cooling processes.

The compatibility with data acquisition cards allows the software to communicate with a variety of external equipment. Typical applications include:

  • Control of sample loading equipment
  • Using multiple strain gauges to measure elongation of a sample
  • Switch testing. Software can use voltage limits to control a test e.g. change direction once switch contact is made
  • Integration into production lines for sharing of part number data and informing a production line if a bad part is found

In addition, built in statistical process control functionality allows continuous process monitoring.

This information has been sourced, reviewed and adapted from materials provided by Lloyd Instruments Ltd.

For more information on this source, please visit Lloyd Instruments Ltd.

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