GB/T 42870-2023 Non-destructive testing—Specific methodology and general evaluation criteria for acoustic emission testing of fibre-reinforced polymers (English Version)
GB/T 42870-2023 Non-destructive testing - Specific methodology and general evaluation criteria for acoustic emission testing of fibre-reinforced polymers
1 Scope
This document describes the general principles of acoustic emission testing (AT) of materials, components, and structures made of fibre-reinforced polymers (FRP) with the aim of materials characterization, proof testing and manufacturing quality control, retesting and in-service testing, and health monitoring.
This document has been designed to describe specific methodology to assess the integrity of fibre-reinforced polymers (FRP), components, or structures or to identify critical zones of high damage accumulation or damage growth under load (e.g. suitable instrumentation, typical sensor arrangements, and location procedures).
It also describes available, generally applicable evaluation criteria for AT of FRP and outlines procedures for establishing such evaluation criteria in case they are lacking.
This document also presents formats for the presentation of acoustic emission test data that allows the application of qualitative evaluation criteria, both online during testing and by post-test analysis, and that simplify comparison of acoustic emission test results obtained from different test sites and organizations.
Note: The structural significance of the acoustic emission cannot in all cases definitely be assessed based on AT evaluation criteria only but can require further testing and assessment (e.g. with other non-destructive test methods or fracture mechanics calculations).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 9712 Non-destructive testing - Qualification and certification of NDT personnel
Note: GB/T 9445-2015, Non-destructive testing - Qualification and certification of NDT personnel (ISO 9712:2012, IDT)
ISO 12716:2001 Non-destructive testing - Acoustic emission inspection - Vocabulary
Note: GB/T 12604.4-2005, Non-destructive testing - Terminology - Terms used in acoustic emisson testing (ISO 12716:2001, IDT)
EN 13477-1 Non-destructive testing - Acoustic emission - Equipment characterisation - Part 1: Equipment description
EN 13477-2 Non-destructive testing - Acoustic emission - Equipment characterisation - Part 2: Verification of operating characteristic
EN 14584 Non-destructive testing - Acoustic emission - Examination of metallic pressure equipment during proof testing - Planar location of AE sources
EN 15495 Non-destructive testing - Acoustic emission - Examination of metallic pressure equipment during proof testing - Zone location of AE sources
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12716:2001 and the following apply.
3.1
fibre
slender and greatly elongated solid material
Note: Typically with an aspect ratio greater than 5 and tensile modulus greater than 20 GPa. The fibres used for continuous (filamentary) or discontinuous reinforcement are usually glass, carbon, or aramide.
3.2
polymer matrix
surrounding macromolecular substance within which fibres are embedded
Note: Polymer matrices are usually thermosets (e.g. epoxy, vinylester polyimide, or polyester) or high-performance thermoplastics [e.g. poly(amide imide), poly(ether ether ketone), or polyimide]. The mechanical properties of polymer matrices are significantly affected by temperature, time, aging, and environment.
3.3
fibre laminate
two-dimensionally element made up of two or more layers (plies of the same material with identical orientation) from fibre-reinforced polymers
Note: They are compacted by sealing under heat and/or pressure. Laminates are stacked together by plane (or curved) layers of unidirectional fibres or woven fabric in a polymer matrix. Layers can be of various thicknesses and consist of identical or different fibre and polymer matrix materials. Fibre orientation can vary from layer to layer.
3.4
fibre-reinforced polymer material; FRP
polymer matrix composite with one or more fibre orientations with respect to some reference direction
Note: Those are usually continuous fibre laminates. Typical as-fabricated geometries of continuous fibres include uniaxial, cross-ply, and angle-ply laminates or woven fabrics. FRPs are also made from discontinuous fibres such as short fibre, long-fibre, or random mat reinforcement.
3.5
delamination
intra- or inter-laminar fracture (crack) in composite materials under different modes of loading
Note: Delamination mostly occurs between the fibre layers by separation of laminate layers with the weakest bonding or the highest stresses under static or repeated cyclic stresses (fatigue), impact, etc. Delamination involves a large number of micro-fractures and secondary effects such as rubbing between fracture surfaces. It develops inside of the composite, without being noticeable on the surface and it is often connected with significant loss of mechanical stiffness and strength.
3.6
micro-fracture (of composites)
occurrence of local failure mechanisms on a microscopic level, such as matrix failure (crazing, cracking), fibre/matrix interface failure (debonding), or fibre pull-out, as well as fibre failure (breakage, buckling)
Note: It is caused by local overstress of the composite. Accumulation of micro-failures leads to macro-failure and determines ultimate strength and life-time.
4 Personnel qualification
It is assumed that acoustic emission testing is performed by qualified and capable personnel. In order to prove this qualification, it is recommended to qualify the personnel in accordance with ISO 9712.
5 Acoustic emission sources and acoustic behaviour
5.1 Acoustic emission source mechanisms
Damage of FRP as a result of micro- and macro-fracture mechanisms produces high acoustic emission activity and intensity making it particularly suitable for acoustic emission testing (AT).
The following are the common failure mechanisms in FRP detected by AT:
——matrix cracking;
——fibre/matrix interface debonding;
——fibre pull-out;
——fibre breakage;
——intra- or inter-laminar crack (delamination/splitting) propagation.
The resulting acoustic emission from FRP depends on many factors, such as material components, laminate lay-up, manufacturing process, discontinuities, applied load, geometry, and environmental test conditions (temperature, humidity, exposure to fluid or gaseous media, or ultraviolet radiation). Therefore, interpretation of acoustic emission under given conditions requires understanding of these factors and experience with acoustic emission from the particular material and construction under known stress conditions.
Fracture of FRP produces burst type acoustic emission, high activity; however, might give the appearance of continuous emission.
For certain types of construction, widely distributed AE sources from matrix or interfacial micro-failure mechanisms under given conditions commonly represent a normal behaviour. This particularly appears during the first loading of a newly manufactured FRP structure, where the composite strain for detection of first significant acoustic emission is in the range of 0.1 % to 0.3 %.
High stiffness optimized composites might shift the onset of first significant acoustic emission towards comparatively high stresses due to the low matrix strain in the composite.
In the case of high-strength composites, acoustic emission from first fibre breakage, apart from other sources, is normally observed at stress levels of about 40 % to 60 % of the ultimate composite strength.
A normal behaviour of FRP structures is also characterized by the occurrence of different regions with alternating higher and lower AE activity, particularly at higher stress levels due to redistribution of local stress.
In the case of a serious discontinuity or other severe stress concentration that influence the failure behaviour of FRP structures, AE activity will concentrate at the affected area, thereby providing a method of detection.
Conversely, discontinuities in areas of the component that remain unstressed as a result of the test and discontinuities that are structurally insignificant will not generate abnormal acoustic emission.
5.2 Wave propagation and attenuation characterization
Acoustic emission signals from waves travelling in large objects are influenced by dispersion and attenuation effects.
Polymer matrix composites are inhomogeneous and often anisotropic materials and, in many applications, designed as thin plates or shells. Wave propagation in thin plates or shells is dominated by plate wave modes (e.g. Lamb waves). The anisotropy is mainly the result of volume and orientation of fibres. This affects wave propagation by introducing directionality into the velocity, attenuation, and large dispersion of plate waves.
Propagation of acoustic waves in FRP results in a significant change of amplitude and frequency content with distance. The extent of these effects will depend upon direction of propagation, material properties, thickness, and geometry of the test object.
Attenuation characterization measurement on representative regions of the test objects in accordance with EN 14584 shall be performed.
The shadowing effect of nozzles and ancillary attachments shall be quantified and transmission through the test fluid shall be taken into consideration.
The attenuation shall be measured in various directions and, if known, in particular parallel and perpendicular to the principal directions of fibre orientation. In the case of a partly filled test object, the attenuation shall be measured above and below the liquid level.
For FRP laminate structures, losses of burst signal peak amplitudes might be in the range of 20 dB to 50 dB after wave propagation of about 500 mm. Attenuation perpendicular to the fibre direction is usually much higher than in the parallel direction.
Note 1: The peak amplitude from a Hsu-Nielsen source can vary with specific viscoelastic properties of the FRP material in different regions of a structure.
Note 2: Hsu-Nielsen source refers to the acoustic emission source produced by the breakage of pencil leads.
5.3 Test temperature
The mechanical (stiffness, strength) and acoustical (wave velocity, attenuation) behaviour of FRP structures and, hence, their AE activity and AE wave characteristic (waveforms, spectra) strongly changes if the test temperature approaches transition temperature ranges of the matrix, such as the ductile-brittle transition (ß-relaxation of semi-crystalline matrices) or the glass-rubber transition (α-relaxation of amorphous matrices).
Standard
GB/T 42870-2023 Non-destructive testing—Specific methodology and general evaluation criteria for acoustic emission testing of fibre-reinforced polymers (English Version)
Standard No.
GB/T 42870-2023
Status
valid
Language
English
File Format
PDF
Word Count
11500 words
Price(USD)
345.0
Implemented on
2023-8-6
Delivery
via email in 1~3 business day
Detail of GB/T 42870-2023
Standard No.
GB/T 42870-2023
English Name
Non-destructive testing—Specific methodology and general evaluation criteria for acoustic emission testing of fibre-reinforced polymers
GB/T 42870-2023 Non-destructive testing - Specific methodology and general evaluation criteria for acoustic emission testing of fibre-reinforced polymers
1 Scope
This document describes the general principles of acoustic emission testing (AT) of materials, components, and structures made of fibre-reinforced polymers (FRP) with the aim of materials characterization, proof testing and manufacturing quality control, retesting and in-service testing, and health monitoring.
This document has been designed to describe specific methodology to assess the integrity of fibre-reinforced polymers (FRP), components, or structures or to identify critical zones of high damage accumulation or damage growth under load (e.g. suitable instrumentation, typical sensor arrangements, and location procedures).
It also describes available, generally applicable evaluation criteria for AT of FRP and outlines procedures for establishing such evaluation criteria in case they are lacking.
This document also presents formats for the presentation of acoustic emission test data that allows the application of qualitative evaluation criteria, both online during testing and by post-test analysis, and that simplify comparison of acoustic emission test results obtained from different test sites and organizations.
Note: The structural significance of the acoustic emission cannot in all cases definitely be assessed based on AT evaluation criteria only but can require further testing and assessment (e.g. with other non-destructive test methods or fracture mechanics calculations).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 9712 Non-destructive testing - Qualification and certification of NDT personnel
Note: GB/T 9445-2015, Non-destructive testing - Qualification and certification of NDT personnel (ISO 9712:2012, IDT)
ISO 12716:2001 Non-destructive testing - Acoustic emission inspection - Vocabulary
Note: GB/T 12604.4-2005, Non-destructive testing - Terminology - Terms used in acoustic emisson testing (ISO 12716:2001, IDT)
EN 13477-1 Non-destructive testing - Acoustic emission - Equipment characterisation - Part 1: Equipment description
EN 13477-2 Non-destructive testing - Acoustic emission - Equipment characterisation - Part 2: Verification of operating characteristic
EN 14584 Non-destructive testing - Acoustic emission - Examination of metallic pressure equipment during proof testing - Planar location of AE sources
EN 15495 Non-destructive testing - Acoustic emission - Examination of metallic pressure equipment during proof testing - Zone location of AE sources
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12716:2001 and the following apply.
3.1
fibre
slender and greatly elongated solid material
Note: Typically with an aspect ratio greater than 5 and tensile modulus greater than 20 GPa. The fibres used for continuous (filamentary) or discontinuous reinforcement are usually glass, carbon, or aramide.
3.2
polymer matrix
surrounding macromolecular substance within which fibres are embedded
Note: Polymer matrices are usually thermosets (e.g. epoxy, vinylester polyimide, or polyester) or high-performance thermoplastics [e.g. poly(amide imide), poly(ether ether ketone), or polyimide]. The mechanical properties of polymer matrices are significantly affected by temperature, time, aging, and environment.
3.3
fibre laminate
two-dimensionally element made up of two or more layers (plies of the same material with identical orientation) from fibre-reinforced polymers
Note: They are compacted by sealing under heat and/or pressure. Laminates are stacked together by plane (or curved) layers of unidirectional fibres or woven fabric in a polymer matrix. Layers can be of various thicknesses and consist of identical or different fibre and polymer matrix materials. Fibre orientation can vary from layer to layer.
3.4
fibre-reinforced polymer material; FRP
polymer matrix composite with one or more fibre orientations with respect to some reference direction
Note: Those are usually continuous fibre laminates. Typical as-fabricated geometries of continuous fibres include uniaxial, cross-ply, and angle-ply laminates or woven fabrics. FRPs are also made from discontinuous fibres such as short fibre, long-fibre, or random mat reinforcement.
3.5
delamination
intra- or inter-laminar fracture (crack) in composite materials under different modes of loading
Note: Delamination mostly occurs between the fibre layers by separation of laminate layers with the weakest bonding or the highest stresses under static or repeated cyclic stresses (fatigue), impact, etc. Delamination involves a large number of micro-fractures and secondary effects such as rubbing between fracture surfaces. It develops inside of the composite, without being noticeable on the surface and it is often connected with significant loss of mechanical stiffness and strength.
3.6
micro-fracture (of composites)
occurrence of local failure mechanisms on a microscopic level, such as matrix failure (crazing, cracking), fibre/matrix interface failure (debonding), or fibre pull-out, as well as fibre failure (breakage, buckling)
Note: It is caused by local overstress of the composite. Accumulation of micro-failures leads to macro-failure and determines ultimate strength and life-time.
4 Personnel qualification
It is assumed that acoustic emission testing is performed by qualified and capable personnel. In order to prove this qualification, it is recommended to qualify the personnel in accordance with ISO 9712.
5 Acoustic emission sources and acoustic behaviour
5.1 Acoustic emission source mechanisms
Damage of FRP as a result of micro- and macro-fracture mechanisms produces high acoustic emission activity and intensity making it particularly suitable for acoustic emission testing (AT).
The following are the common failure mechanisms in FRP detected by AT:
——matrix cracking;
——fibre/matrix interface debonding;
——fibre pull-out;
——fibre breakage;
——intra- or inter-laminar crack (delamination/splitting) propagation.
The resulting acoustic emission from FRP depends on many factors, such as material components, laminate lay-up, manufacturing process, discontinuities, applied load, geometry, and environmental test conditions (temperature, humidity, exposure to fluid or gaseous media, or ultraviolet radiation). Therefore, interpretation of acoustic emission under given conditions requires understanding of these factors and experience with acoustic emission from the particular material and construction under known stress conditions.
Fracture of FRP produces burst type acoustic emission, high activity; however, might give the appearance of continuous emission.
For certain types of construction, widely distributed AE sources from matrix or interfacial micro-failure mechanisms under given conditions commonly represent a normal behaviour. This particularly appears during the first loading of a newly manufactured FRP structure, where the composite strain for detection of first significant acoustic emission is in the range of 0.1 % to 0.3 %.
High stiffness optimized composites might shift the onset of first significant acoustic emission towards comparatively high stresses due to the low matrix strain in the composite.
In the case of high-strength composites, acoustic emission from first fibre breakage, apart from other sources, is normally observed at stress levels of about 40 % to 60 % of the ultimate composite strength.
A normal behaviour of FRP structures is also characterized by the occurrence of different regions with alternating higher and lower AE activity, particularly at higher stress levels due to redistribution of local stress.
In the case of a serious discontinuity or other severe stress concentration that influence the failure behaviour of FRP structures, AE activity will concentrate at the affected area, thereby providing a method of detection.
Conversely, discontinuities in areas of the component that remain unstressed as a result of the test and discontinuities that are structurally insignificant will not generate abnormal acoustic emission.
5.2 Wave propagation and attenuation characterization
Acoustic emission signals from waves travelling in large objects are influenced by dispersion and attenuation effects.
Polymer matrix composites are inhomogeneous and often anisotropic materials and, in many applications, designed as thin plates or shells. Wave propagation in thin plates or shells is dominated by plate wave modes (e.g. Lamb waves). The anisotropy is mainly the result of volume and orientation of fibres. This affects wave propagation by introducing directionality into the velocity, attenuation, and large dispersion of plate waves.
Propagation of acoustic waves in FRP results in a significant change of amplitude and frequency content with distance. The extent of these effects will depend upon direction of propagation, material properties, thickness, and geometry of the test object.
Attenuation characterization measurement on representative regions of the test objects in accordance with EN 14584 shall be performed.
The shadowing effect of nozzles and ancillary attachments shall be quantified and transmission through the test fluid shall be taken into consideration.
The attenuation shall be measured in various directions and, if known, in particular parallel and perpendicular to the principal directions of fibre orientation. In the case of a partly filled test object, the attenuation shall be measured above and below the liquid level.
For FRP laminate structures, losses of burst signal peak amplitudes might be in the range of 20 dB to 50 dB after wave propagation of about 500 mm. Attenuation perpendicular to the fibre direction is usually much higher than in the parallel direction.
Note 1: The peak amplitude from a Hsu-Nielsen source can vary with specific viscoelastic properties of the FRP material in different regions of a structure.
Note 2: Hsu-Nielsen source refers to the acoustic emission source produced by the breakage of pencil leads.
5.3 Test temperature
The mechanical (stiffness, strength) and acoustical (wave velocity, attenuation) behaviour of FRP structures and, hence, their AE activity and AE wave characteristic (waveforms, spectra) strongly changes if the test temperature approaches transition temperature ranges of the matrix, such as the ductile-brittle transition (ß-relaxation of semi-crystalline matrices) or the glass-rubber transition (α-relaxation of amorphous matrices).