Flat-cladding fibre bragg grating sensors for large strain fatigue tests

In the design of mechanical components, the fatigue of material are of particular importance as ~80% of metal failures in practice arise from fatigue. The fatigue life is generally determined from low cyclic fatigue tests at large strain. This thesis developed a novel flat-cladding Fiber Bragg Grating sensor array applied in the characterization of LCF properties of three different specimens. With a new bonding process, large strain amplitude measurement of up to [plus or minus] 8000 μ [epsilon] was achieved in the Aluminum base metal and asymmetric hysteresis loops at high strain amplitudes due to twinning in compression and subsequent detwinning in tension was observed in Magnesium alloy. Moreover, an abnormal softening and hardening variation in different zone of friction stir welded Aluminum alloy was discovered throught the FBG sensor distribution. The validity shows that the FBG sensor a vital tool in the LCF tests at large strain amplitudes. Furthermore, due to its small size, the multiplexed FBG sensor array could also be applied to the measurements of strain distribution.

Flat-cladding fibre bragg grating sensors for large strain fatigue tests

In the design of mechanical components, the fatigue of material are of particular importance as ~80% of metal failures in practice arise from fatigue. The fatigue life is generally determined from low cyclic fatigue tests at large strain. This thesis developed a novel flat-cladding Fiber Bragg Grating sensor array applied in the characterization of LCF properties of three different specimens. With a new bonding process, large strain amplitude measurement of up to [plus or minus] 8000 μ [epsilon] was achieved in the Aluminum base metal and asymmetric hysteresis loops at high strain amplitudes due to twinning in compression and subsequent detwinning in tension was observed in Magnesium alloy. Moreover, an abnormal softening and hardening variation in different zone of friction stir welded Aluminum alloy was discovered throught the FBG sensor distribution. The validity shows that the FBG sensor a vital tool in the LCF tests at large strain amplitudes. Furthermore, due to its small size, the multiplexed FBG sensor array could also be applied to the measurements of strain distribution.

Flat-Cladding Fiber Bragg Grating Sensors for Large Strain Amplitude Fatigue Tests

We have successfully developed a flat-cladding fiber Bragg grating sensor for large cyclic strain amplitude tests of up to ±8,000 με. The increased contact area between the flat-cladding fiber and substrate, together with the application of a new bonding process, has significantly increased the bonding strength. In the push-pull fatigue tests of an aluminum alloy, the plastic strain amplitudes measured by three optical fiber sensors differ only by 0.43% at a cyclic strain amplitude of ±7,000 με and 1.9% at a cyclic strain amplitude of ±8,000 με. We also applied the sensor on an extruded magnesium alloy for evaluating the peculiar asymmetric hysteresis loops. The results obtained were in good agreement with those measured from the extensometer, a further validation of the sensor.

Flat-Cladding Fiber Bragg Grating Sensors for Large Strain Amplitude Fatigue Tests

We have successfully developed a flat-cladding fiber Bragg grating sensor for large cyclic strain amplitude tests of up to ±8,000 με. The increased contact area between the flat-cladding fiber and substrate, together with the application of a new bonding process, has significantly increased the bonding strength. In the push-pull fatigue tests of an aluminum alloy, the plastic strain amplitudes measured by three optical fiber sensors differ only by 0.43% at a cyclic strain amplitude of ±7,000 με and 1.9% at a cyclic strain amplitude of ±8,000 με. We also applied the sensor on an extruded magnesium alloy for evaluating the peculiar asymmetric hysteresis loops. The results obtained were in good agreement with those measured from the extensometer, a further validation of the sensor.