The cellular level mode I fracture behaviour of spruce and birch in the RT crack propagation system

Holzforschung ◽  
2016 ◽  
Vol 70 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Crack Propagation ◽  
Fracture Behaviour ◽  
Crack Tip ◽  
Cellular Level ◽  
Image Correlation ◽  
Environmental Scanning ◽  
Mode I ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Displacement Fields

Abstract The effect of the microscopic structure and the moisture content (MC) of wood on its fracture behaviour has been investigated. Green and air-dried spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood were subjected to pure mode I loading in the radial- tangential (RT) crack propagation system. Tests were carried out in situ in an environmental scanning electron microscope to observe crack propagation at the cellular level. Crack-tip displacement fields were computed by digital image correlation, and crack propagation was observed from the images captured during testing. Both the MC and the microscopic structure were found to affect the fracture process. In the air-dried birch and spruce, only microcracking caused large displacements ahead of the crack-tip. In spruce, the microcracking zone was larger than in birch. In green birch and spruce, microcracking was less evident than in the air-dried specimens, and in some cases, there were notable deformations in a few cells ahead of the crack-tip before crack extension. Microcracking is considered to be the main toughening mechanism in spruce and birch in the RT crack propagation system.

Mode I Fracture Behaviour on the Growth Ring Scale and Cellular Level of Spruce (Picea abies [L.] Karst.) and Beech (Fagus sylvatica L.) Loaded in the TR Crack Propagation System

Holzforschung ◽  
2003 ◽  
Vol 57 (6) ◽  
pp. 653-660 ◽  
Author(s):  
K. Frühmann ◽  
I. Burgert ◽  
S. E. Stanzl-Tschegg ◽  
E. K. Tschegg
Keyword(s):  
Crack Propagation ◽  
Fracture Behaviour ◽  
Growth Ring ◽  
Level Density ◽  
Cellular Level ◽  
Environmental Scanning ◽  
Mode I ◽  
Atmospheric Conditions ◽  
Damage And Fracture ◽  
And Function

Summary Crack propagation in wood is strongly influenced by the microscopic structure of the material. The relationship between structure and function with regard to damage and fracture behaviour can only be understood with a sufficiently fine level of examination. An experimental approach to perform micro-wedge splitting tests on spruce and beech inside the chamber of an Environmental Scanning Electron Microscope and under atmospheric conditions is presented. The specimens are loaded in mode I in the TR crack propagation system. Based on the load-displacement diagram, the characteristic parameters of fracture energy, critical load and initial elasticity are determined. The load and displacement data for the in situ experiments are related to the obtained ESEM images and allow a discussion of the fracture process on the cellular level. Density was found to be an important factor for fracture mode and several crack arresting phenomena depending on the variation of elasticity could be identified.

The fracture behavior of birch and spruce in the radial-tangential crack propagation direction at the scale of the growth ring

Holzforschung ◽  
2013 ◽  
Vol 67 (6) ◽  
pp. 673-681 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Mouth Opening ◽  
Crack Tip ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Crack Model ◽  
Pure Mode ◽  
Displacement Fields ◽  
Tip Displacement

Abstract Crack-tip displacement fields have been computed based on digital image correlation for spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood, which were submitted to pure mode I loading in the RT-direction under both green and air-dried conditions. Moreover, crack propagation was modeled based on both linear elastic fracture mechanics (LEFM) and nonlinear fracture mechanics, relying on the fictitious crack model (FCM). The measured and modeled load versus the crack-mouth opening displacement (CMOD) curves and displacement fields were compared. In the case of spruce, the load-CMOD curves simulated by the FCM coincide well with the measured ones. On the contrary, measured near crack-tip displacement fields in both green and air-dried spruce are better comparable with the LEFM predictions than with the FCM predictions. In the case of green birch, the simulated FCM curve follows the measured curve quite well, but in air-dried birch the simulated FCM curve has a better fit than the LEFM-curve only before maximum load. In birch, the FCM predicts the displacement fields better than the LEFM. In both species, moisture content has a big effect on the softening behavior. In both spruce and birch, the FCM overestimates the displacements ahead of crack tip, whereas the LEFM model underestimates the displacements.

The effect of temperature and moisture content on the fracture behaviour of spruce and birch

Holzforschung ◽  
2016 ◽  
Vol 70 (4) ◽  
pp. 369-376 ◽  
Author(s):  
Pekka Tukiainen ◽  
Mark Hughes
Keyword(s):  
Moisture Content ◽  
Crack Propagation ◽  
Fracture Behaviour ◽  
Mouth Opening ◽  
Climatic Conditions ◽  
Effect Of Temperature ◽  
Crack Mouth Opening Displacement ◽  
Microscopic Structure ◽  
Pure Mode ◽  
Opening Displacement

Abstract The fracture behaviour of wood is affected by, amongst other factors, its microscopic structure, moisture content and temperature, as well as the direction of crack propagation. Spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) compact tension specimens were subjected to pure mode I loading in both the radial-tangential (RT) and tangential-radial (TR) orientations under four climatic conditions. The effect of microscopic structure on crack propagation was observed, and the “crack mouth opening displacement vs. load” histories were recorded, from which characteristic fracture parameters were calculated. The fracture surfaces were subsequently examined by optical microscopy. In both species, distinct changes in the fracture behaviour were observed as moisture content (MC) and temperature (T) were varied. The results were specific for the wood species, but MC and T influenced fracture behaviour in a similar way. The effects were more pronounced in birch than in spruce. Elevated T and MC did not affect the failure mode, except in the case of spruce in the RT orientation.

Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

2018 ◽  
Author(s):  
João Ferreira ◽  
José A. F. O. Correia ◽  
Grzegorz Lesiuk ◽  
Sergio Blasón González ◽  
Maria Cristina R. Gonzalez ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Mixed Mode ◽  
Pressure Vessels ◽  
Mode I ◽  
Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

scholarly journals Investigation by Digital Image Correlation of Mixed Mode I and II Fracture Behavior of Metallic IASCB Specimens with Additive Manufactured Crack-Like Notch

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 400 ◽  
Author(s):  
Ivo Campione ◽  
Tommaso Maria Brugo ◽  
Giangiacomo Minak ◽  
Jelena Janković Tomić ◽  
Nebojša Bogojević ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Mixed Mode ◽  
Fracture Behavior ◽  
Selective Laser Sintering ◽  
Local Stress ◽  
Fatigue Loading ◽  
Image Correlation ◽  
Mode I ◽  
Displacement Fields

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined asymmetrical semi-circular specimen subjected to three points loading (IASCB) was used, allowing to cover a wide variety of Mode I and II combinations. The effectiveness of manufacturing crack-like notches via the SLS technique in metals was evaluated by comparing the obtained experimental results with the ones obtained with pre-cracks induced by fatigue loading. The investigation was carried out by using the digital image correlation (DIC) technique, that allowed the evaluation of the full displacement fields around the crack tip. The displacement field was then used to compute the stress intensity factors (SIFs) for various combinations of Mode I and II, via a fitting technique which relies on the Williams’ model for the displacement. The SIFs obtained in this way were compared to the results obtained with the conventional critical load method. The results showed that the discrepancy between the two methods reduces by ranging from Mode I to Mode II loading condition. Finally, the experimental SIFs obtained by the two methods were described by the mixed mode local stress criterium.

Effect of Graphene Addition on Crack Propagation Resistance in Glass Fibre Reinforced Polymer Matrix Composite

2018 ◽  
Author(s):  
G. V. Vigneshwaran ◽  
S. Balasivanandha Prabu ◽  
R. Paskaramoorthy
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Fiber Surface ◽  
Dip Coating ◽  
Image Correlation ◽  
Mode I ◽  
Molding Process ◽  
Mode I Fracture ◽  
Crack Propagation Resistance ◽  
Mode I Fracture Toughness

The effect of graphene nanoplatelets (GNPs) on enhancing the interlaminar fracture toughness of glass fiber/epoxy composites was investigated. The GnPs were physically deposited on the fiber surface by the dip coating technique. The composites were fabricated by hand layup technique followed by the compression molding process. Mode-I fracture test was conducted on the composite specimens. Crack propagation was studied by the digital image correlation (DIC) technique. Mode-I fracture toughness for composites loaded with 0.5 wt.% GnPs showed improvement by an average of 60% when compared to the pristine composites. It is concluded that the addition of GnPs produces a strong fiber/matrix interface bonding which effectively limits the crack propagation.

Crack propagation in a PVA dual-crosslink hydrogel: Crack tip fields measured using digital image correlation

2019 ◽  
Vol 138 ◽  
pp. 103158 ◽  
Author(s):  
Mincong Liu ◽  
Jingyi Guo ◽  
Zhilong Li ◽  
Chung-Yuen Hui ◽  
Alan T. Zehnder
Keyword(s):  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Crack Tip ◽  
Image Correlation ◽  
Crack Tip Fields

scholarly journals Identification and Prediction of Mixed-Mode Fatigue Crack Path in High Strength Low Alloy Steel

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 504
Author(s):  
Jie Zhang ◽  
Cedric Kiekens ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Digital Image Correlation ◽  
Crack Propagation ◽  
Digital Image ◽  
Mixed Mode ◽  
Standardized Test ◽  
Crack Tip ◽  
Shear Loading ◽  
Image Correlation ◽  
Crack Trajectory

The trajectory of fatigue crack growth is influenced by many parameters and can be irregular due to changes in stress distribution or in material properties as the crack progresses. Images of the surface of a standardized test specimen can be used to visualize the crack trajectory in a non-destructive way. Accurately identifying the location of the crack tip, however, is challenging and requires devoted image postprocessing. In this respect, digital image correlation allows to obtain full field displacement and strain fields by analysing changes of digital images of the same sample at different stages of loading. This information can be used for the purpose of crack tip tracking. This paper presents a combined experimental-numerical study of detection and prediction of fatigue crack propagation path by means of digital image correlation (DIC) and the extended finite element method (X-FEM). Experimental validation and analyses are carried out on a modified C(T) specimen in which a curved crack trajectory is triggered by introducing mixed-mode (tension + shear) loading. The developed tools are used for validating an automated framework for crack propagation prediction.

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