# Mov Lecture - 4 Physical Principle of Strain Gauges, Photoelasticity and MoirÃ©

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Lecture - 4 Physical Principle of Strain Gauges, Photoelasticity and Moiré

This video is Module of the Overview of Experimental Stress Analysis and part of the Lecture series on Experimental Stress Analysis by Prof.K.Ramesh,Department of Applied Mechanics,IIT Madras.

Brainbuxa.com appreciates and recognises the work done by professors of IIT for delivering great lectures and enhancing Free Education worldwide through the initiative NPTEL. For more videos , do visit http://nptel.iitm.ac.in

NPTEL provides E-learning through online Web and Video courses in Engineering, Science and humanities streams. The mission of NPTEL is to enhance the quality of Engineering education in the country by providing free online courseware.

COURSE OUTLINE

The course covers the basic aspects of experimental stress analysis that includes exhaustive treatment of the most versatile techniques like photoelasticity and strain gauges and also a brief introduction to the emerging techniques like digital image correlation. In addition it also provides the fundamental aspects of six different experimental techniques such as Moiré, Brittle Coatings, Holography, Speckle Methods, Thermoelastic Stress Analysis and Caustics.

COURSE ORGANISATION

Modules 1 :: Overview of Experimental Stress Analysis

Modules 2 :: Transmission Photoelasticity

Modules 3 :: Introduction to Three Dimensional Photoelasticity and Digital Photoelasticity

Modules 4 :: Photoelastic Coatings and Brittle Coatings

Modules 5 :: Strain Gauges

Modules 6 :: Discussion Section

COURSE DETAIL

Lecture 1 :: Overview of Experimental Stress Analysis

Concepts Covered :: Overview of experimental stress analysis, Stress analysis – Analytical, Numerical and Experimental approaches, Specific domain of these approaches, Advantages and disadvantages.

Lecture 2 :: Optical Methods Work as Optical Computers

Concepts Covered :: Optical methods work as optical computers, Direct information provided by various experimental methods – brief description, Visual appreciation of field information – Listing of various problems of different complexity.

Lecture 3 :: Stress, Strain and Displacement Fields

Concepts Covered :: Stress, Strain and Displacement fields for various problems, Beam under pure bending, Analytical solution, Fringe contours from various experimental methods, Disc under diametral compression – Analytical solution, Fringe contours from various experimental techniques, Clamped circular plate under a central load – Analytical solution, Fringe contours from various experimental techniques.

Lecture 4 :: Physical Principle of Strain Gauges, Photoelasticity and Moiré

Concepts Covered :: Spanner tightening a nut – completeness of a numerical solution, comparison with photoelastic fringes. Physical principle behind various experimental techniques, Strain Gauges, Photoelasticity, Grids for determining plastic strains, Geometric moiré, grating details – u and v displacements, Demonstration of fringes due to translation and rotation of gratings of various types

Lecture 5 :: Introduction to Moiré, Brittle Coatings and Holography

Concepts Covered :: Brief introduction to Moiré, Brittle coatings and Holography. Difference between normal photography and holography, Visualising the depth information, Formation of speckles due to illumination by a laser, Rainbow hologram.

Lecture 6 :: Hologram Interferometry, Speckle Methods

Concepts Covered :: Hologram interferometry, Steps in a double exposure hologram interferometry, Speckle methods, Objective speckles, Subjective speckles

Lecture 7 :: Introduction to Shearography, TSA, DIC and Caustics

Concepts Covered :: Brief introduction to Speckle interferometry, Shearography, Thermoelastic Stress Analysis (TSA), Digital Image Correlation (DIC) and Caustics. Caustics in a tea cup, dimple formation, Class demonstration of Caustic experiment.

Lecture 8 :: Fringe Patterns – Richness of Qualitative Information

Concepts Covered :: Coherent gradient sensor, Naming of experimental methods, Fringe patterns – Richness of qualitative information, Information provided by fringe thickness, density. Optical methods for quality inspection, Comparison of various designs – Streamline fillet, Key technologies that have influenced Experimental Mechanics

Lecture 9 :: Multi-Scale Analysis in Experimental Mechanics

Concepts Covered :: Multi-scale analysis in experimental mechanics, Trends in experimental mechanics, Discussion on selection of an experimental technique,

Lecture 10 :: Selection of an Experimental Technique

Concepts Covered :: Discussion on selection of an experimental technique contd., References. Review of solid mechanics, definition of free surface, ambiguity in associating the correct value of principal stress direction to the magnitude of the principal stress, Eigen value approach or use of Mohr’s circle, Shear distribution in a three point bend specimen

Lecture 11 :: Introduction to Transmission Photoelasticity

Concepts Covered :: Physical principle, Historical development, Various branches of photoelasticity, Birefringence, Nature of light, Polarisation, Methods to get polarized light, Understanding polarization, Class experiment on showing crossed polarizers, Passage of light through isotropic media.

Lecture 12 :: Ordinary and Extraordinary Rays

Concepts Covered :: Snell’s laws, Passage of light through crystalline media, Demonstration of birefringence effect of Calcite prism, Influence on the role of optical axis of the crystal, Light ellipse.

Lecture 13 :: Light Ellipse, Passage of Light Through a Crystal Plate

Concepts Covered :: Light ellipse (contd.) Retardation plates and wave plates, Historical development on polarization optics, Dichroism, Sheet polarisers

Lecture 14 :: Retardation Plates, Stress-optic Law

Concepts Covered :: Sheet polarisers contd., Retardation plates and wave plates, Quarter wave, Half wave and Full wave plates, Stress-optic law, Maximum stress information obtainable by photoelasticity.

Lecture 15 :: Plane Polariscope

Concepts Covered :: Plane polariscope, Logical explanation of formation of fringes, Understanding isochromatics, isoclinics. Intensity of light transmitted in a plane polariscope by trigonometric resolution.

Lecture 16 :: Jones Calculus

Concepts Covered :: Jones calculus, Rotation matrix, Retardation matrix, Representation of a retarder, Elements of the polariscope, Analysis of plane polariscope by Jones calculus, Circular polariscope, Dark and bright fields.

Lecture 17 :: Circular Polariscope

Concepts Covered :: Circular polariscope (contd.), Intensity of light transmitted by Jones calculus, Various optical arrangements possible, Demonstration of a commercial polariscope, Use of white light, Colour code, Tint of passage, Storage of photoelastic materials, Time-edge effect, Summary of photoelastic fringes.

Lecture 18 :: Determination of Photoelastic Parameters at an Arbitrary Point

Concepts Covered :: Review of colour code, Determination of photoelastic parameters at an arbitrary point, Compensation techniques, Babinet–Soleil compensator in

detail, Steps in Tardy’s Method of compensation.

Lecture 19. Tardy’s Method of Compensation

Concepts Covered :: Tardy’s method of compensation, Brief exposure to digital photoelasticity, Need for calibration of photoelastic materials, advantage of circular disk, Calibration of photoelastic model materials, Stress field in a circular disc under diametral compression.

Lecture 20. Calibration of Photo elastic Materials

Concepts Covered :: Conventional approach to calibration, Linear least squares analysis, Sampled least squares, Introduction to the use of Image processing techniques, Image sampling and quantization

Lecture 21. Fringe Thinning Methodologies

Concepts Covered :: Fringe thinning methodologies, Thresholding to find fringe areas, Binary based and intensity based algorithms, Chen & Taylor algorithm for one scanning direction, Fringe skeletonisation, Global fringe thinning algorithm, Experimental evaluation, Theoretical reconstruction of fringe pattern, Opening remarks on comments on fringe ordering.

Lecture 22. Fringe Ordering in Photoelasticity

Concepts Covered :: Importance of accurate evaluation of material stress fringe value, Global fringe thinning – summary, Comments on fringe ordering (contd.), Features of isochromatic and isoclinic fringe field, Positive and negative isotropic points, Role of principles of solid mechanics in fringe ordering, Identification of zeroth fringe order.

Lecture 23. Miscellaneous Topics in Transmission Photoelasticity

Concepts Covered :: Resolving the ambiguity on the principal stress direction, Determination of the sign of the boundary stress, Compatibility conditions, Role of elastic constants on stress field, Model to prototype relations, Properties of photoelastic model materials.

Lecture 24. Three Dimensional Photoelasticity

Concepts Covered :: Three dimensional photoelasticity, Stress freezing, Slicing, Application to a complex problem, Integrated photoelasticity, Principle of optical equivalence.

Lecture 25. Overview of Digital Photoelasticity

Concepts Covered :: Introduction to digital photoelasticity, Use of colour information for quantitative analysis, Three Fringe Photoelasticity (TFP), Refined TFP (RTFP) to solve slow time variant problems. Paradigm shift in data processing, Processing of intensity data for photoelastic data extraction, Overview of digital photoelasticity, Ten-step method, Understanding phasemaps.

Lecture 26. Introduction to Photoelastic Coatings

Concepts Covered :: Photoelastic coatings, Historical development, Optical arrangements, Photoelastic strain gauges, Strain-optic relation for coating, Evaluation of coating and specimen stresses.

Lecture 27. Correction Factors for Photoelastic Coatings

Concepts Covered :: Correction factors for photoelastic coatings, Correction factor for bending, Combined in-plane and bending loads, Correction factor for torsion, Correction factor for pressure vessel.

Lecture 28. Coating Materials, Selection of Coating Thickness, Industrial Application of Photoelastic Coatings

Concepts Covered :: Correction factors – Summary, Handling mismatch of Poisson’s ratio, Coating materials, Properties of photoelastic coating materials, Selection of the coating thickness, Maximum fringe order obtainable, Use of photoelastic coatings to solve a range of problems of practical interest

Lecture 29. Calibration of Photoelastic Coatings, Introduction to Brittle Coatings

Concepts Covered :: Demonstration of photoelastic coating test, Calibration of photoelastic coatings, Compact displacement controlled loading jig. Historical development of brittle coatings, Methodology of brittle coatings, Crack patterns produced by direct loading, Uniaxial, Biaxial and Isotropic stress fields, Steps in brittle coating tests, Coating selection, Surface preparation.

Lecture 30. Analysis of Brittle Coatings

Concepts Covered :: Undercoating, Application of the coating, Drying. Coating stresses, Uniaxial specimen stress, Nature of coating stress, Calibration of brittle coatings, Influence of Poisson’s ratio mismatch, Crack patterns by refrigeration, Crack patterns by relaxation, Stresscoat.

Lecture 31. Introduction to Strain Gauges

Concepts Covered :: Analysis of Isoentatic data, Strain Gauges: Physical principle, Historical development, Development of SR-4 gauges, Strain sensitivity of a conductor, Gauge construction, Gauge length, Gauge length error in measurement, Thumb rule in selection of gauge length, Commonly used strain gauge materials.

Lecture 32. Strain Sensitivity of a Strain Gauge, Bridge Sensitivity, Rosettes

Concepts Covered :: Strain sensitivity of a strain gauge, Transverse sensitivity factor, Gauge factor, Experimental determination of gauge factor, Wheatstone bridge, Strain measurement options, Bridge sensitivity, Bridge factor, Accuracy achievable in Foil strain gauges, Linearity, Hysteresis and Zero shift, Determination of strain at a point, Three element rectangular rosette.

Lecture 33. Strain Gauge Alloys, Carriers and Adhesives

Concepts Covered :: Delta rosette, Metallic alloys commonly employed, Advance, Isoelastic alloy, Karma alloy, Thermally induced apparent strain, Nichrome-D, Strain gauge carriers, Types, Cements for bonding a strain gauge: Cynoacrylate, Epoxy cements and Polyester cements

Lecture 34. Performance of Strain Gauge System

Concepts Covered :: Ceramic cements, High temperature strain gauge, Flame spraying Rokide process, Strain gauge linearity, Hysteresis, Drift, Stability, Heat dissipation, Allowable power density, Selection of bridge voltage, Sensitivity of gauge to temperature, Strain sensitivity of a conductor as a function of temperature.

Lecture 35. Temperature Compensation, Two-wire and Three-wire Circuits

Concepts Covered :: Temperature compensation, Temperature compensated gauges, Measurement techniques: Two-wire circuit, Gauge factor desensitization, Role of change in temperature, Three-wire circuit, Benefits of three-wire circuits.

Lecture 36. Strain Gauge Selection

Concepts Covered :: Selection compromises, Strain gauge designation systems, Various gauge patterns for different applications, Guidelines for strain gauge selection.

Lecture 37. Bonding of a Strain Gauge

Concepts Covered :: Temperature effects guiding the selection of certain parameters, Importance of following a bonding procedure, Surface preparation: Strain gauge installation kit, Solvent degreasing, Surface abrading, Layout lines, Surface conditioning, Neutralizing. Strain gauge bonding: Strain gauge handling, Strain gauge alignment, Catalyst application, Bonding with adhesive.

Lecture 38. Soldering, Accounting for Transverse Sensitivity Effects

Concepts Covered :: Masking, Tinning, Soldering, Application of protective coating, Testing the installation, Transverse sensitivity, Actual and apparent strains, Corrections for transverse strain effects for the case of known ratio of the transverse strain to the axial strain.

Lecture 39. Correction Factors for Special Applications

Concepts Covered :: Corrections for transverse strain effects for a general case, T–rosette, Rectangular rosette. Effect of hydrostatic pressure, Effect of nuclear radiation, Effect of high temperature, Effect of cryogenic temperature, Effect of strain cycling, Environmental effects.

Lecture 40. Special Gauges

Concepts Covered :: Environmental effects contd., Torque gauge, Stress gauge, Single element strain gauge as stress gauge, Evaluation of SIF by strain gauges, Strip gauge, Single element strain gauge to evaluate SIF. Summary of the course.

Lecture 41. Questions & Answers

Concepts Covered :: A few questions from the whole course were discussed.

Lecture - 1 Overview of Experimental Stress Analysis

This video is Module of the Overview of Experimental Stress Analysis and part of the Lecture series on Experimental Stress Analysis by Prof.K.Ramesh,Department of Applied Mechanics,IIT Madras.

Brainbuxa.com appreciates and recognises the work done by professors of IIT for delivering great lectures and enhancing Free Education worldwide through the initiative NPTEL. For more videos , do visit http://nptel.iitm.ac.in

NPTEL provides E-learning through online Web and Video courses in Engineering, Science and humanities streams. The mission of NPTEL is to enhance the quality of Engineering education in the country by providing free online courseware.

COURSE OUTLINE

The course covers the basic aspects of experimental stress analysis that includes exhaustive treatment of the most versatile techniques like photoelasticity and strain gauges and also a brief introduction to the emerging techniques like digital image correlation. In addition it also provides the fundamental aspects of six different experimental techniques such as Moiré, Brittle Coatings, Holography, Speckle Methods, Thermoelastic Stress Analysis and Caustics.

COURSE ORGANISATION

Modules 1 :: Overview of Experimental Stress Analysis

Modules 2 :: Transmission Photoelasticity

Modules 3 :: Introduction to Three Dimensional Photoelasticity and Digital Photoelasticity

Modules 4 :: Photoelastic Coatings and Brittle Coatings

Modules 5 :: Strain Gauges

Modules 6 :: Discussion Section

COURSE DETAIL

Lecture 1 :: Overview of Experimental Stress Analysis

Concepts Covered :: Overview of experimental stress analysis, Stress analysis – Analytical, Numerical and Experimental approaches, Specific domain of these approaches, Advantages and disadvantages.

Lecture 2 :: Optical Methods Work as Optical Computers

Concepts Covered :: Optical methods work as optical computers, Direct information provided by various experimental methods – brief description, Visual appreciation of field information – Listing of various problems of different complexity.

Lecture 3 :: Stress, Strain and Displacement Fields

Concepts Covered :: Stress, Strain and Displacement fields for various problems, Beam under pure bending, Analytical solution, Fringe contours from various experimental methods, Disc under diametral compression – Analytical solution, Fringe contours from various experimental techniques, Clamped circular plate under a central load – Analytical solution, Fringe contours from various experimental techniques.

Lecture 4 :: Physical Principle of Strain Gauges, Photoelasticity and Moiré

Concepts Covered :: Spanner tightening a nut – completeness of a numerical solution, comparison with photoelastic fringes. Physical principle behind various experimental techniques, Strain Gauges, Photoelasticity, Grids for determining plastic strains, Geometric moiré, grating details – u and v displacements, Demonstration of fringes due to translation and rotation of gratings of various types

Lecture 5 :: Introduction to Moiré, Brittle Coatings and Holography

Concepts Covered :: Brief introduction to Moiré, Brittle coatings and Holography. Difference between normal photography and holography, Visualising the depth information, Formation of speckles due to illumination by a laser, Rainbow hologram.

Lecture 6 :: Hologram Interferometry, Speckle Methods

Concepts Covered :: Hologram interferometry, Steps in a double exposure hologram interferometry, Speckle methods, Objective speckles, Subjective speckles

Lecture 7 :: Introduction to Shearography, TSA, DIC and Caustics

Concepts Covered :: Brief introduction to Speckle interferometry, Shearography, Thermoelastic Stress Analysis (TSA), Digital Image Correlation (DIC) and Caustics. Caustics in a tea cup, dimple formation, Class demonstration of Caustic experiment.

Lecture 8 :: Fringe Patterns – Richness of Qualitative Information

Concepts Covered :: Coherent gradient sensor, Naming of experimental methods, Fringe patterns – Richness of qualitative information, Information provided by fringe thickness, density. Optical methods for quality inspection, Comparison of various designs – Streamline fillet, Key technologies that have influenced Experimental Mechanics

Lecture 9 :: Multi-Scale Analysis in Experimental Mechanics

Concepts Covered :: Multi-scale analysis in experimental mechanics, Trends in experimental mechanics, Discussion on selection of an experimental technique,

Lecture 10 :: Selection of an Experimental Technique

Concepts Covered :: Discussion on selection of an experimental technique contd., References. Review of solid mechanics, definition of free surface, ambiguity in associating the correct value of principal stress direction to the magnitude of the principal stress, Eigen value approach or use of Mohr’s circle, Shear distribution in a three point bend specimen

Lecture 11 :: Introduction to Transmission Photoelasticity

Concepts Covered :: Physical principle, Historical development, Various branches of photoelasticity, Birefringence, Nature of light, Polarisation, Methods to get polarized light, Understanding polarization, Class experiment on showing crossed polarizers, Passage of light through isotropic media.

Lecture 12 :: Ordinary and Extraordinary Rays

Concepts Covered :: Snell’s laws, Passage of light through crystalline media, Demonstration of birefringence effect of Calcite prism, Influence on the role of optical axis of the crystal, Light ellipse.

Lecture 13 :: Light Ellipse, Passage of Light Through a Crystal Plate

Concepts Covered :: Light ellipse (contd.) Retardation plates and wave plates, Historical development on polarization optics, Dichroism, Sheet polarisers

Lecture 14 :: Retardation Plates, Stress-optic Law

Concepts Covered :: Sheet polarisers contd., Retardation plates and wave plates, Quarter wave, Half wave and Full wave plates, Stress-optic law, Maximum stress information obtainable by photoelasticity.

Lecture 15 :: Plane Polariscope

Concepts Covered :: Plane polariscope, Logical explanation of formation of fringes, Understanding isochromatics, isoclinics. Intensity of light transmitted in a plane polariscope by trigonometric resolution.

Lecture 16 :: Jones Calculus

Concepts Covered :: Jones calculus, Rotation matrix, Retardation matrix, Representation of a retarder, Elements of the polariscope, Analysis of plane polariscope by Jones calculus, Circular polariscope, Dark and bright fields.

Lecture 17 :: Circular Polariscope

Concepts Covered :: Circular polariscope (contd.), Intensity of light transmitted by Jones calculus, Various optical arrangements possible, Demonstration of a commercial polariscope, Use of white light, Colour code, Tint of passage, Storage of photoelastic materials, Time-edge effect, Summary of photoelastic fringes.

Lecture 18 :: Determination of Photoelastic Parameters at an Arbitrary Point

Concepts Covered :: Review of colour code, Determination of photoelastic parameters at an arbitrary point, Compensation techniques, Babinet–Soleil compensator in

detail, Steps in Tardy’s Method of compensation.

Lecture 19. Tardy’s Method of Compensation

Concepts Covered :: Tardy’s method of compensation, Brief exposure to digital photoelasticity, Need for calibration of photoelastic materials, advantage of circular disk, Calibration of photoelastic model materials, Stress field in a circular disc under diametral compression.

Lecture 20. Calibration of Photo elastic Materials

Concepts Covered :: Conventional approach to calibration, Linear least squares analysis, Sampled least squares, Introduction to the use of Image processing techniques, Image sampling and quantization

Lecture 21. Fringe Thinning Methodologies

Concepts Covered :: Fringe thinning methodologies, Thresholding to find fringe areas, Binary based and intensity based algorithms, Chen & Taylor algorithm for one scanning direction, Fringe skeletonisation, Global fringe thinning algorithm, Experimental evaluation, Theoretical reconstruction of fringe pattern, Opening remarks on comments on fringe ordering.

Lecture 22. Fringe Ordering in Photoelasticity

Concepts Covered :: Importance of accurate evaluation of material stress fringe value, Global fringe thinning – summary, Comments on fringe ordering (contd.), Features of isochromatic and isoclinic fringe field, Positive and negative isotropic points, Role of principles of solid mechanics in fringe ordering, Identification of zeroth fringe order.

Lecture 23. Miscellaneous Topics in Transmission Photoelasticity

Concepts Covered :: Resolving the ambiguity on the principal stress direction, Determination of the sign of the boundary stress, Compatibility conditions, Role of elastic constants on stress field, Model to prototype relations, Properties of photoelastic model materials.

Lecture 24. Three Dimensional Photoelasticity

Concepts Covered :: Three dimensional photoelasticity, Stress freezing, Slicing, Application to a complex problem, Integrated photoelasticity, Principle of optical equivalence.

Lecture 25. Overview of Digital Photoelasticity

Concepts Covered :: Introduction to digital photoelasticity, Use of colour information for quantitative analysis, Three Fringe Photoelasticity (TFP), Refined TFP (RTFP) to solve slow time variant problems. Paradigm shift in data processing, Processing of intensity data for photoelastic data extraction, Overview of digital photoelasticity, Ten-step method, Understanding phasemaps.

Lecture 26. Introduction to Photoelastic Coatings

Concepts Covered :: Photoelastic coatings, Historical development, Optical arrangements, Photoelastic strain gauges, Strain-optic relation for coating, Evaluation of coating and specimen stresses.

Lecture 27. Correction Factors for Photoelastic Coatings

Concepts Covered :: Correction factors for photoelastic coatings, Correction factor for bending, Combined in-plane and bending loads, Correction factor for torsion, Correction factor for pressure vessel.

Lecture 28. Coating Materials, Selection of Coating Thickness, Industrial Application of Photoelastic Coatings

Concepts Covered :: Correction factors – Summary, Handling mismatch of Poisson’s ratio, Coating materials, Properties of photoelastic coating materials, Selection of the coating thickness, Maximum fringe order obtainable, Use of photoelastic coatings to solve a range of problems of practical interest

Lecture 29. Calibration of Photoelastic Coatings, Introduction to Brittle Coatings

Concepts Covered :: Demonstration of photoelastic coating test, Calibration of photoelastic coatings, Compact displacement controlled loading jig. Historical development of brittle coatings, Methodology of brittle coatings, Crack patterns produced by direct loading, Uniaxial, Biaxial and Isotropic stress fields, Steps in brittle coating tests, Coating selection, Surface preparation.

Lecture 30. Analysis of Brittle Coatings

Concepts Covered :: Undercoating, Application of the coating, Drying. Coating stresses, Uniaxial specimen stress, Nature of coating stress, Calibration of brittle coatings, Influence of Poisson’s ratio mismatch, Crack patterns by refrigeration, Crack patterns by relaxation, Stresscoat.

Lecture 31. Introduction to Strain Gauges

Concepts Covered :: Analysis of Isoentatic data, Strain Gauges: Physical principle, Historical development, Development of SR-4 gauges, Strain sensitivity of a conductor, Gauge construction, Gauge length, Gauge length error in measurement, Thumb rule in selection of gauge length, Commonly used strain gauge materials.

Lecture 32. Strain Sensitivity of a Strain Gauge, Bridge Sensitivity, Rosettes

Concepts Covered :: Strain sensitivity of a strain gauge, Transverse sensitivity factor, Gauge factor, Experimental determination of gauge factor, Wheatstone bridge, Strain measurement options, Bridge sensitivity, Bridge factor, Accuracy achievable in Foil strain gauges, Linearity, Hysteresis and Zero shift, Determination of strain at a point, Three element rectangular rosette.

Lecture 33. Strain Gauge Alloys, Carriers and Adhesives

Concepts Covered :: Delta rosette, Metallic alloys commonly employed, Advance, Isoelastic alloy, Karma alloy, Thermally induced apparent strain, Nichrome-D, Strain gauge carriers, Types, Cements for bonding a strain gauge: Cynoacrylate, Epoxy cements and Polyester cements

Lecture 34. Performance of Strain Gauge System

Concepts Covered :: Ceramic cements, High temperature strain gauge, Flame spraying Rokide process, Strain gauge linearity, Hysteresis, Drift, Stability, Heat dissipation, Allowable power density, Selection of bridge voltage, Sensitivity of gauge to temperature, Strain sensitivity of a conductor as a function of temperature.

Lecture 35. Temperature Compensation, Two-wire and Three-wire Circuits

Concepts Covered :: Temperature compensation, Temperature compensated gauges, Measurement techniques: Two-wire circuit, Gauge factor desensitization, Role of change in temperature, Three-wire circuit, Benefits of three-wire circuits.

Lecture 36. Strain Gauge Selection

Concepts Covered :: Selection compromises, Strain gauge designation systems, Various gauge patterns for different applications, Guidelines for strain gauge selection.

Lecture 37. Bonding of a Strain Gauge

Concepts Covered :: Temperature effects guiding the selection of certain parameters, Importance of following a bonding procedure, Surface preparation: Strain gauge installation kit, Solvent degreasing, Surface abrading, Layout lines, Surface conditioning, Neutralizing. Strain gauge bonding: Strain gauge handling, Strain gauge alignment, Catalyst application, Bonding with adhesive.

Lecture 38. Soldering, Accounting for Transverse Sensitivity Effects

Concepts Covered :: Masking, Tinning, Soldering, Application of protective coating, Testing the installation, Transverse sensitivity, Actual and apparent strains, Corrections for transverse strain effects for the case of known ratio of the transverse strain to the axial strain.

Lecture 39. Correction Factors for Special Applications

Concepts Covered :: Corrections for transverse strain effects for a general case, T–rosette, Rectangular rosette. Effect of hydrostatic pressure, Effect of nuclear radiation, Effect of high temperature, Effect of cryogenic temperature, Effect of strain cycling, Environmental effects.

Lecture 40. Special Gauges

Concepts Covered :: Environmental effects contd., Torque gauge, Stress gauge, Single element strain gauge as stress gauge, Evaluation of SIF by strain gauges, Strip gauge, Single element strain gauge to evaluate SIF. Summary of the course.

Lecture 41. Questions & Answers

Concepts Covered :: A few questions from the whole course were discussed.