Size effects in defect-free Douglas fir

1990 ◽  
Vol 17 (2) ◽  
pp. 238-242 ◽  
Author(s):  
Borg Madsen
Keyword(s):  
Size Effects ◽  
Volume Effect ◽  
Douglas Fir ◽  
Material Behavior ◽  
Empirical Methods ◽  
Clear Wood ◽  
Weakest Link ◽  
Link Theory ◽  
Structural Engineers ◽  
Free Material

This paper describes experimental work on size effects occurring in defect-free Douglas fir and suggests empirical methods for modelling these. It was found, contrary to present belief, that the size effects could best be described as a volume effect. It was also found that wet and dry materials behaved very differently with respect to size effects. Defect-free material represents the stronger and more expensive range of materials available to the structural engineers. It is, therefore, important that the material behavior be better understood in order to create structures that are both safe and economical. Key words: size effects, clear wood, defect-free wood, volume effect, length effects, load configuration effect, moisture content, weakest link theory.

Size effects in timber explained by a modified weakest link theory

1986 ◽  
Vol 13 (2) ◽  
pp. 218-232 ◽  
Author(s):  
Borg Madsen ◽  
Andrew H. Buchanan
Keyword(s):  
Size Effects ◽  
Design Method ◽  
Bending Test ◽  
Test Results ◽  
New Approach ◽  
Weakest Link ◽  
Link Theory ◽  
Tension Members ◽  
Depth Effects ◽  
Good Agreement

This paper represents a new approach to size effects in timber. The design process in Canadian Standards Association code CAN3-086-M80 allows for size effects in shear and in tension but not in bending. A large number of bending test results arc analyzed in this paper to show that size effects in bending are very important. A modification is made to the traditional weakest link theory for size effects to reflect the anisotropic nature of timber. Good agreement is obtained between tests and theory. The theory enables us to compare tests with different spans and (or) load configurations with an understanding not previously possible. Results from several large testing programs are used to quantify the theory. For bending members, length effects and load configuration effects are found to be much more important than depth effects, and a simple design method is proposed. Information for tension members is less comprehensive; nevertheless, a tentative suggestion for the design of those members is included.

Statistical Size Effects on Compressive Strength and Mechanical Behavior of Concrete

2017 ◽  
Vol 754 ◽  
pp. 317-320 ◽  
Author(s):  
Chi Cong Vu ◽  
Jérôme Weiss ◽  
Olivier Plé ◽  
David Amitrano
Keyword(s):  
Compressive Strength ◽  
Size Effects ◽  
Aggregate Size ◽  
Dissipated Energy ◽  
Compression Tests ◽  
Weakest Link ◽  
Link Theory ◽  
Long Time ◽  
Compressive Strength Of Concrete ◽  
Main Shortcoming

The size effect on strength of concrete has been studied for a long time from various approaches. In particular, the weakest-link theory remains nowadays the basic tool to interpret statistical size effects, i.e. how the probability of failure under a given stress depends on external size. The main shortcoming of Weibull’s theory is that the activation of fracture from the weakest flaw is assumed to set the final strength, i.e. possible interactions between microcracks and defects during progressive damage are implicitly neglected. The objective of this study is to determine experimentally the influence of “external” (sample) size and “internal” (microstructural) size on compressive strength of concrete. For this purpose, more than 250 uniaxial compression tests were conducted on concrete specimens with two different cylindrical sizes (110×220 mm and 160×320 mm) and prepared from three different compositions (mean aggregate size and proportion). The relationships between compressive strength, dissipated energy up to failure in one hand, and microstructural as well as specimen sizes on the other hand, were analyzed statistically. This demonstrated the failure of the weakest-link approach to describe size effects on compressive strength of concrete.

THE ECONOMICS OF PRUNING

1954 ◽  
Vol 30 (2) ◽  
pp. 197-214 ◽  
Author(s):  
J. H. G. Smith
Keyword(s):  
Shell Thickness ◽  
Tree Mortality ◽  
Douglas Fir ◽  
Early Age ◽  
Clear Wood ◽  
Tools And Techniques ◽  
International Rule

The need for pruning of Douglas fir is urgent. Research has shown that acceptable tools and techniques are available and has evaluated the effects of pruning. This report considers the costs and possible profit in pruning and concludes that for site III Douglas fir, pruning is profitable in all d.b.h. classes from 4" to 22".Volume and growth relationships between clear-shell thickness and diameter at the time of pruning are determined using both the International rule with ¼-inch kerf for board feet and the Smalian formula for cubic feet. A correction is made for slab allowance to give the net clear-wood scale of sawn material.Factors affecting lumber value of pruned trees are illustrated by examples of Douglas fir with and without natural pruning. Pruning profit per tree and per M.f.b.m. are calculated from value comparisons of clear and knotty lumber in pruned and unpruned trees. A formula is presented to aid in the choice of trees and stands to prune in the Douglas fir and other regions. Largest returns may be expected when rapidly growing trees are pruned at an early age. Additional profits may be secured by growing clear shells larger than four inches in diameter. Pruning is shown to be a safe and profitable investment at 2½ per cent without considering increased returns which may come from salvage of pruned-tree mortality and acceleration of growth by thinnings.

A Modified Gradient Plasticity Theory for Micro-Bending and Micro-Torsion Size Effects

2004 ◽  
Author(s):  
George Z. Voyiadjis ◽  
Rashid K. Abu Al-Rub
Keyword(s):  
Size Effects ◽  
Scale Parameter ◽  
Plasticity Theory ◽  
Material Behavior ◽  
Length Scale Parameter ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Non Local ◽  
Material Length Scale ◽  
Material Length

The definition and magnitude of the intrinsic length scale are keys to the development of the theory of plasticity that incorporates size effects. Gradient plasticity theory with a material length scale parameter is successfully in capturing the size dependence of material behavior at the micron scale. However, a fixed value of the material length-scale is not always realistic and that different problems could require different values. Moreover, a linear coupling between the local and non-local terms in the gradient plasticity theory is not always realistic and that different problems could require different couplings. A generalized gradient plasticity model with a non-fixed length scale parameter is proposed. This model assesses the sensitivity of predictions in the way in which the local and non-local parts are coupled. The proposed model gives good predictions of the size effect in micro-bending tests of thin films and micro-torsion tests of thin wires.

Size effects on material behavior in microforming

2009 ◽  
Vol 2 (S1) ◽  
pp. 625-628 ◽  
Author(s):  
C. Barbier ◽  
S. Thibaud ◽  
F. Richard ◽  
P. Picart
Keyword(s):  
Size Effects ◽  
Material Behavior

scholarly journals Modeling of the Size Effects on the Behavior of Metals in Microscale Deformation Processes

2006 ◽  
Vol 129 (3) ◽  
pp. 470-476 ◽  
Author(s):  
Gap-Yong Kim ◽  
Jun Ni ◽  
Muammer Koç
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
Material Behavior ◽  
Accurate Analysis ◽  
Analysis And Design ◽  
Scaling Model ◽  
Simple Tension ◽  
Two Parameters

For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/mesoscale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the feature/specimen size effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with three separate experiments obtained from previous research: a simple compression with a round specimen, a simple tension with a round specimen, and a simple tension in sheet metal. The predicted results had a very good agreement with the experiments. Quantification of the miniaturization effect has been achieved by introducing two parameters, α and β, which can be determined by the scaling parameter n, to the Hall–Petch equation. The scaling model offers a simple way to model the size effect down to length scales of a couple of grains and to extend the use of continuum plasticity theories to micro/mesolength scales.

Time-Dependent Forming Characteristics in Pt/NiO/Pt Stack Structures for Resistive Random Access Memory

2012 ◽  
Vol 1430 ◽  
Author(s):  
Yusuke Nishi ◽  
Tatsuya Iwata ◽  
Daisuke Horie ◽  
Tsunenobu Kimoto
Keyword(s):  
Thin Films ◽  
Random Access ◽  
Resistive Random Access Memory ◽  
Time Dependent ◽  
Access Memory ◽  
Forming Process ◽  
Weakest Link ◽  
Link Theory ◽  
Nio Thin Film ◽  
Forming Characteristics

ABSTRACTConstant voltage Time-Dependent Forming (TDF) measurements in as-deposited Pt/NiO/Pt stack structures have been conducted. From TDF characteristics, formation of conductive filaments at forming process by applying voltage follows weakest link theory. Furthermore, weakest spots are almost randomly distributed in NiO thin films according to Poisson statistics, each of which can contribute conductive paths locally generated. A “percolating layer” in which the conductive filaments percolate by applying voltage may exist in the NiO thin film. The thickness of the layer is much smaller than that of NiO thin films.

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