BS ISO 18249 pdf download – Non-destructive testing —Acoustic emission testing —Specific methodology andgeneral evaluation criteriafor testing of fibre-reinforce dpolymers.
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 ito entry: Typically with an aspect ratio greater than Sand tensile modulus greater than 20 GPa. The fibres used for continuous (filamentary) or discontinuous reinforcement arc usually glass, carbon, or aramide.
polymer matrix
surrounding macromolecular substance within which libres are embedded
Note Ito entry: Polymer matrices are usually thermosets (e.g. epoxy. vinylester polylmide, or polyester) or high- performance thermopbstics (e.g. pvly(amide imkle), poly(ether ether ketonc), or polyimidej. 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 Ito entry: 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 vahous 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 Ito entry: Those are usually continuous fibre laminates. Typical as-fabncated geometries of continuous fibres indudeuniaxial. cross-ply, and angle-ply laminates orwoven fabrics. FRPs are also made fron discontinuous fibres such as short fibre, long-fibre, or r.indom Inst reinforcement.
3.5
delamInation
intra- or inter-laminar fracture (crack) in composite materials under different modes of loading
Note I to entry: Delamination mostly occurs between the fibre layers by separation of laminate layers with the weakest bonding orthe 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)
owience of local failure mechanisms oti microscopic level, such as matrix failure (crazing, cracking).
fibre/matrix interface failure (debondmg), or fibre pull.out. as well as fibre failure (breakage, buckling)
Note ito entry: It is caused by local overatress of the composite, Accumulation of micro-failures leads to macro- failure and determines ultimate strength and life-time.
The attenuation shall he 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 The peak amplitude from a Hsu•Niciscn source can vary with specific viscodastic properties of the FRP material in different regions ola structure.
5.3 Test temperature
The mechanical (stlfTness, 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 (.relaxation of semi-crystalline matrices) or the glass-rubber transition (a-relaxation of amorphous matrices).
Therefore, the test temperature has to be considered for data evaluation and interpretation of AE test results, as well as in the loading procedure.
5.4 Source location
Accurate source location in FRP structures is difficult. Due to the high attenuation in composite materials, the AF hits only the nearest sensor in most practical monitoring situations on structures. For this reason, zone location Is usually the main source of location information. The use of zone location, however, does not prevent linear or planar location ofAE sources that have sufficient energy to hit several sensors to allow location by time arrival differences. Linear or planar location Is a useful supplement, predominantly for the location of higher energy emissions. Great care shall be taken with both methods where timing information is used for location since the velocity of sound and attenuation will usually change with the direction of propagation in FRP.
BS ISO 18249 pdf download – Non-destructive testing —Acoustic emission testing —Specific methodology andgeneral evaluation criteriafor testing of fibre-reinforce dpolymers
