Untersuchungen zur Ermittlung der Bruchzähigkeit and MDF-Platten

Abstract

Determination of the fracture toughness of MDF hoardFracture toughness is a measure for the crack resistance of a material. This paper presents the results of an analysis on the infuence of density and moisture content on fracture toughness of MDF. Fracture toughness was measured using ASTM E 399 with CT-specimens (parallel to the board direction). Acoustic emission analysis and scanning electron microscopy (SEM) were used to assess the kind of fracture and the fracture surface. Higher fracture toughness values were found with increasing density. An increase in moisture content caused a decrease in fracture toughness. Acoustic emission analysis showed no clear results regarding the kind of fracture of MDF. According to SEM fibres were nearly torn out of the MDF board. Fractures of fibres, as they occur in particleboard, were not observed.

Fracture energy vs. internal bond strength – mechanical characterization of wood-based panels

“…Which of the two concepts is applied depends on the relationship of process zone and the specimen geometry. In terms of wood, LEFM is known and widely used (Porter 1964, Patton-Mallory and Cramer 1987, Valentin and Adjanohoun 1992, Niemz et al 1997, Niemz and Diener 1999. The usage of wood as a testing material and the knowledge about its non-isotropic material characteristics makes small sized specimens questionable.…”

Mechanical and fracture properties of particleboard

“…However, only a few studies investigates the fracture toughness of PB [8][9][10]. The same like in the case of MDF, different values of fracture toughness were obtained: Matsumoto and Nairn [11] 2.57 MPa•m 1/2 for density of 609 kg/m 3 , respectively 3.77 MPa•m 1/2 for density of 769 kg/m 3 using Compact Tension (CT) specimens, while for wedge splitting specimens and a density of 710 kg/m 3 Niemz et al [12] obtained 1.81 MPa•m 1/2 . Fewer investigations were carried out on mixed mode fracture toughness of PB and MDF, [13].…”

Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method

“…Only a few experiments analyzing the fracture toughness of MDF were found in the literature. Niemz et al , [ 23 , 24 ] used CT specimens according to ASTM 399 to analyze the stress intensity factor. The specimens were oriented parallel to the board plane and yielded K IC values of 1.81 ± 0.33 MPam 0.5 (CV 18.2%) for a density of 710 kg/m 3 (20 °C/65% RH) and numbers in a range of 0.36 ± 0.03 MPam 0.5 (8.3% CV) to 1.29 ± 0.06 MPam 0.5 (CV 4.7%) with a density of 500 kg/m 3 , depending on the equilibrium moisture content, which varied from 21.4% to 3.5%.…”

“…Although it is reported that wood [ 5 ] and wood based panels [ 6 , 7 ] show non-linear characteristics, which is due to the large process zone and fiber bridging, nevertheless the concept of linear fracture mechanics for measuring toughness is widely accepted [ 5 , 15 , 23 , 24 ].…”