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Flex

Wallace-MRPRA Fatigue Tester - F13

Features   Measures fatigue resistance   Results not influenced by heat build up   Standard Schopper rings used as samples   Strain deformation adjustable from 0 to 300% in 12.5 % steps   12 samples can be accommodated   Each sample has dedicated sample to indicate sample failure   Robust, easily serviced design   To find out more about this product contact Wallace

Introduction

The Wallace-MRPRA Fatigue Tester measures the fatigue resistance of rubber under controlled conditions of cyclic deformation. Failure of the test piece is the result of crack grcwth and the design of the machine and the choice of test piece precludes the possibility of test results being influenced by heat build-up.

The test piece is cyclically deformed in tension at a constant rate of 300 cycles per minute until failure. The number of cycles is recorded and quoted as a measure of the fatigue resistance of the material. The severity of the test is adjustable in steps between zero deformation and 300% maximum.

Effect of Relaxation

Set is a major problem when measuring fatigue resistance. If no adjustment is made to compensate for "set" the severity of the test is changed. If adjustment is made a new variable is introduced which is difficult to allow for.

Tests have indicated that "set" up to a maximum of 10% does not affect results beyond the 'scatter' which will normally be experienced. If the "set" exceed 10% the results must be treated with considerable caution, it also suggests that the material is unsuitable for applications where the strain averaged over the cyclic deformation is not zero.

It is recommended that no adjustment be made to compensate for 'set'.

Description of Machine

The machine consists of a heavy steel fabrication with a frame carrying two banks of test piece pulleys. The test pieces are vertical in two rows of six. As one row of test pieces is extending the other is relaxing which ensures reasonable mechanical balance.

Each test piece passes round four pulleys, to form a rectangle with a pulley at each corner. This effectively overcomes the problem of friction encountered when only two pulleys are used.

The driving mechanism is arranged to give sinusoidal motion to the moving pulleys. The "throw" of the mechanism can be changed in steps each representing 12.5% strain deformation. The position of the stationary test piece pulleys can be changed in steps each representing 12.5% strain deformation.

A separate electrically operated counter is provided for each test sample. The counter reads to 999999 representing cycles x 100. Each counter stops immediately the test piece it represents fails. The machine continues operating without attention until the last test piece fails, when an automatic cut-out stops the drive motor.

For safety, the machine cannot be operated with the door open and automatic stops ensure the machine is stationary when the operator has access to moving parts.

Specification

See the table below for a run-down of this product's specifications.