Monitoring Pre-Stressed Composites Using Optical Fibre Sensors
Residual stresses in fibre reinforced composites can give rise to a number of undesired effects such as loss of dimensional stability and premature fracture. Hence, there is significant merit in developing processing techniques to mitigate the development of residual stresses. However, tracking and...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2016-05-01
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| Series: | Sensors |
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| Online Access: | http://www.mdpi.com/1424-8220/16/6/777 |
| _version_ | 1798042106819772416 |
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| author | Sriram Krishnamurthy Rodney A. Badcock Venkata R. Machavaram Gerard F. Fernando |
| author_facet | Sriram Krishnamurthy Rodney A. Badcock Venkata R. Machavaram Gerard F. Fernando |
| author_sort | Sriram Krishnamurthy |
| collection | DOAJ |
| description | Residual stresses in fibre reinforced composites can give rise to a number of undesired effects such as loss of dimensional stability and premature fracture. Hence, there is significant merit in developing processing techniques to mitigate the development of residual stresses. However, tracking and quantifying the development of these fabrication-induced stresses in real-time using conventional non-destructive techniques is not straightforward. This article reports on the design and evaluation of a technique for manufacturing pre-stressed composite panels from unidirectional E-glass/epoxy prepregs. Here, the magnitude of the applied pre-stress was monitored using an integrated load-cell. The pre-stressing rig was based on a flat-bed design which enabled autoclave-based processing. A method was developed to end-tab the laminated prepregs prior to pre-stressing. The development of process-induced residual strain was monitored in-situ using embedded optical fibre sensors. Surface-mounted electrical resistance strain gauges were used to measure the strain when the composite was unloaded from the pre-stressing rig at room temperature. Four pre-stress levels were applied prior to processing the laminated preforms in an autoclave. The results showed that the application of a pre-stress of 108 MPa to a unidirectional [0]16 E-glass/913 epoxy preform, reduced the residual strain in the composite from −600 µε (conventional processing without pre-stress) to approximately zero. A good correlation was observed between the data obtained from the surface-mounted electrical resistance strain gauge and the embedded optical fibre sensors. In addition to “neutralising” the residual stresses, superior axial orientation of the reinforcement can be obtained from pre-stressed composites. A subsequent publication will highlight the consequences of pres-stressing on fibre alignment, the tensile, flexural, compressive and fatigue performance of unidirectional E-glass composites. |
| first_indexed | 2024-04-11T22:30:54Z |
| format | Article |
| id | doaj.art-2606869cbd9d41099aa1b35812360d89 |
| institution | Directory Open Access Journal |
| issn | 1424-8220 |
| language | English |
| last_indexed | 2024-04-11T22:30:54Z |
| publishDate | 2016-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Sensors |
| spelling | doaj.art-2606869cbd9d41099aa1b35812360d892022-12-22T03:59:24ZengMDPI AGSensors1424-82202016-05-0116677710.3390/s16060777s16060777Monitoring Pre-Stressed Composites Using Optical Fibre SensorsSriram Krishnamurthy0Rodney A. Badcock1Venkata R. Machavaram2Gerard F. Fernando3Engineering System Department, Royal Military College of Science, Shrivenham SN6 8LA, UKSchool of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UKSchool of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UKSchool of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UKResidual stresses in fibre reinforced composites can give rise to a number of undesired effects such as loss of dimensional stability and premature fracture. Hence, there is significant merit in developing processing techniques to mitigate the development of residual stresses. However, tracking and quantifying the development of these fabrication-induced stresses in real-time using conventional non-destructive techniques is not straightforward. This article reports on the design and evaluation of a technique for manufacturing pre-stressed composite panels from unidirectional E-glass/epoxy prepregs. Here, the magnitude of the applied pre-stress was monitored using an integrated load-cell. The pre-stressing rig was based on a flat-bed design which enabled autoclave-based processing. A method was developed to end-tab the laminated prepregs prior to pre-stressing. The development of process-induced residual strain was monitored in-situ using embedded optical fibre sensors. Surface-mounted electrical resistance strain gauges were used to measure the strain when the composite was unloaded from the pre-stressing rig at room temperature. Four pre-stress levels were applied prior to processing the laminated preforms in an autoclave. The results showed that the application of a pre-stress of 108 MPa to a unidirectional [0]16 E-glass/913 epoxy preform, reduced the residual strain in the composite from −600 µε (conventional processing without pre-stress) to approximately zero. A good correlation was observed between the data obtained from the surface-mounted electrical resistance strain gauge and the embedded optical fibre sensors. In addition to “neutralising” the residual stresses, superior axial orientation of the reinforcement can be obtained from pre-stressed composites. A subsequent publication will highlight the consequences of pres-stressing on fibre alignment, the tensile, flexural, compressive and fatigue performance of unidirectional E-glass composites.http://www.mdpi.com/1424-8220/16/6/777pre-stresscompositesautoclaveextrinsic fibre Fabry-Perotfibre Bragg gratingsStraintemperatureresidual stresses |
| spellingShingle | Sriram Krishnamurthy Rodney A. Badcock Venkata R. Machavaram Gerard F. Fernando Monitoring Pre-Stressed Composites Using Optical Fibre Sensors Sensors pre-stress composites autoclave extrinsic fibre Fabry-Perot fibre Bragg gratings Strain temperature residual stresses |
| title | Monitoring Pre-Stressed Composites Using Optical Fibre Sensors |
| title_full | Monitoring Pre-Stressed Composites Using Optical Fibre Sensors |
| title_fullStr | Monitoring Pre-Stressed Composites Using Optical Fibre Sensors |
| title_full_unstemmed | Monitoring Pre-Stressed Composites Using Optical Fibre Sensors |
| title_short | Monitoring Pre-Stressed Composites Using Optical Fibre Sensors |
| title_sort | monitoring pre stressed composites using optical fibre sensors |
| topic | pre-stress composites autoclave extrinsic fibre Fabry-Perot fibre Bragg gratings Strain temperature residual stresses |
| url | http://www.mdpi.com/1424-8220/16/6/777 |
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