Damage evolution and acoustic emission of wood at tension perpendicular to fiber

Abstract

This paper presents the tracing of damage evolution in spruce loaded in tension perpendicular to ®ber direction by means of acoustic emission (AE) analysis. The 2 dimensional burst source location in cross-sectional slabs of boards utilized full wave form recording of AE signals monitored by six simultaneously triggered multiple resonant longitudinal (p±)wave sensors and fast transient recorder PC cards. The location algorithm was based on the minimization of the run time differences between experimental and theoretical signal travel times. The latter accounted for the global polar material anisotropy leading to considerably variable off-axis wave velocities along the wave propagation paths, assumed to be straight; the employed orthotropic on-and off-axis p-wave velocities were obtained experimentally from ultrasound pulse measurements. Below 50% of the ultimate load generally very few burst events were recorded. At further increased load, burst agglomerations were predominantly associated to local areas of elevated stresses here resulting from the speci®c con®guration of anisotropy and loading. For all specimens a distinct burst localisation was obtained in the range of 80 to 90% of the ultimate load, coinciding well with the theoretically highest stressed areas of the fracture plane at brittle failure. The correlation of AE event rates with global strain allowed a tracing of the damage evolution especially when events in con®ned areas are regarded. Distinct damage localisation was then denoted by a clear AE rate increase, however, not accompanied by a global stiffness change. The investigations revealed that failure of spruce ± and most probably of similar softwoods ± in tension perpendicular to grain, although being very brittle from a macroscopic perspective, is preceded by progressive and localizing damage evolution on the micro-level which can be traced accurately in space and time by acoustic emission burst source analysis.

Damage evolution in wood – pattern recognition based on acoustic emission (AE) frequency spectra

“…A multitude of approaches focuses on this issue. The conventional AE analysis investigates the parameters of the AE signals in the time domain (Figure 1a) by means of AE signal amplitudes (Debaise et al 1966;Ansell 1982;Ando et al 1992a;Cunderlik et al 1996;Lee et al 1996;Aicher et al 2001;Kim et al 2005;Rosner 2012). Other studies focused on the AE frequency features (frequency domain, see Figure 1b) (Ogino et al 1986;Tyree and Sperry 1989;Reiterer et al 2000;Jakiela et al 2008).…”

Acoustic emission to detect xylophagous insects in wooden musical instrument

“…Many studies deal with the relationship between the stress level in wood under flexural loading and AE energy due to the fracture process [4] using ultrasonic sensors with a nominative frequency of 200 kHz. Aicher et al [5] have shown that using several ultrasonic sensors it was possible to locate the damage before the rupture. The influence of external parameters has been also reported, especially the variation in ambient relative humidity [6][7][8][9].…”

Acoustic emission measurements and lattice simulations of microfracture events in spruce

“…This difference was attributed to differences in the fracture process zone formation in the two types of material. Aicher et al (2001) tracked damage localization phenomena by AE source locations, whereas Landis and Whittaker (2000) used an analysis of elastic waveform energy to measure the fraction of specimen fracture energy that is measured as AE energy.…”