Mode I fracture and acoustic emission of softwood and hardwood

The Mode I fracture behaviour of two softwoods (spruce and pine) and three hardwoods (alder, oak and ash) was studied in the RL crack propagation syst em using the splitting test in combination with monitoring acoustic emissio n (AE) activity. Test parameters measured included notch tensile strength, specific fracture energy, characteristic length and AE cumulative counts, A E amplitudes as well as parameters characterizing the frequency spectra of the emitted acoustic emission events. The notch tensile strength was found to correlate with density. The specific fracture energy and characteristic length showed the different crack propagation process between the softwoods and hardwoods. The softwoods fractured in a more ductile way and the hardw oods showed a more linear elastic behaviour. This finding was supported by the AE measurements showing much less cumulative counts for the hardwoods i ndicating that less microcracks were formed and that processes like fiber b ridging were not so effective. Differences in the frequency domain of the A E signals between softwoods and hardwoods could not be detected.