Experimental study of the destruction in CFRP laminates at the macro-level by acoustic emission method

Abstract

The author conducted experiments using the method of acoustic emission under uniaxial tension of specimens of CFRP laminates with different stacking, geometry and stress concentration. The influence of a mutual arrangement of the material destruction zone and the extensometer installation site on the nonlinear deformation is revealed. It is shown that the damage accumulation process is highly informative when determining the energy of AE pulses. The possibility of visualizing the formation and development of destruction zones in orthogonal directions, as well as the possibility of determining the moment of crack start from the apex of the notch during splitting, is established. The mechanism of alternating stress relaxation in two developed zones of destruction is revealed. The paper shows a high degree of correlation between mechanic and acoustic-emission events. Finally, the author suggests assessing the mechanical state of material with the account of obtained damages by the degree of its integrity (one to zero) depending on the load history, its individual geometric features and stress concentration.

Mechanical Behavior of Active and Passive Strain Sections in CFRP Laminate under Uniaxial Tension

“…Nonlinear "strain-stress" relationship during mechanical tension of CFRP laminates with unidirectional, quasi-isotropic and other structures is a particular property of this type of composite materials [1][2][3][4][5][6][7]. Nonlinearity is often poorly expressed and is almost invisible on the strain diagrams [8]. Therefore, it is believed that the material obeys Hooke's law, which establishes a direct ratio between stresses and strains, and a proportionality coefficient E (material's modulus of elasticity).…”