|
PF Adhesive Coverage
1
/D
t(
m
m
/M
P
a
)
1% 25% 100%
1% 25% 100%
VTC Strand
Normal Strand
Mechanical Properties of
OSB, OSL
2900
3400
3900
4400
4900
5400
5900
0.00
0.01
0.02
0.03
0.04
0.05
1/D
t
(mm/MPa)
M
O
E
(
M
P
a
)
1% Glue
25% Glue
PF
20%
10%
0%
30%
Adequate
Correspondence to
Experiment
Figure 1.3. Flow chart of tasks in this research.
1.5 Technical Objectives of the Research
The overall goal of this research was to develop the Material Point Method
(MPM) as a potential tool for numerical modeling of wood and wood-based composites
that is capable for modeling many details of wood anatomy and wood-based composites
8
processing including mechanical properties, strand undulation, and glue-line stiffness
effects. In order to achieve this goal the following specific objectives were pursued:
I.
Determine the role of glue-lines for OSB in the panel mechanical properties
II.
Evaluate the effect on mechanical properties of wood-based composites of
using enhanced wood strands (such viscoelastic thermal compression [VTC]
strands) in wood-based composites.
In order to complete these objectives, the following specific tasks were pursued:
1.
Develop a new experimental technique to measure the interfacial stiffness
properties for strand-to-strand bonds with varying amounts of adhesive
coverage.
2.
Construct a Material Point Method (MPM) model to study mechanical
properties of OSB with bond-line interfaces.
3.
Expand MPM to include elastic and plastic behavior with a work hardening
law to simulate OSB compaction.
4.
Study the effect of adhesive coverage on the mechanical stiffness of glued
strands in wood-based composites (from discrete droplets to a continuous
bondline).
5.
Develop homogenized rule-of-mixtures model to help interpret OSB panel
mechanical properties and MPM results.
6.
Investigate the effect of interfacial properties of adhesives on mechanical
behavior of OSB panels loaded in bending or in tension.
7.
Study the density profile of OSB panels as a function of selected variables.
1.6 Rationale and Significance
Due to non-renewable and non-sustainable nature of synthetic composites such as
carbon fiber and glass fiber composites, there is increasing demand for renewable
composites panels for structured applications, such as engineered wood panels like OSB.
Currently, wood resources in the United States are limited more and more to smaller
diameter trees. The manufacturer that produces engineered OSB products can use small
9
log sizes (less than 20 year old trees). Furthermore, wood-strand composites such as OSB
and oriented strand lumber (OSL) are able to enhance their properties by tailoring to
specific applications (e.g., I-beam and Glulam for high load applications). With the
advantages of engineering design of wood products, new wood composites can be
established. Therefore, knowing the factors that control the mechanical properties of
wood-strand composites is key for successful design of new products.
Specifically, this research can predict the mechanical properties of wood-strand
composites in terms of its morphology and adhesive coverage (interfacial properties).
This prediction has not been possible before. The experimental and modeling work in this
research has opened a window of opportunity for engineering design of structural wood-
based composites based on constituents properties of the raw materials.
1.7 Structure of the Dissertation
This dissertation is divided into seven chapters, including this introductory
chapter. Each chapter discusses the results of individual tasks or part of the overall model
from the tasks shown in Figure 1.3. Each chapter contains an abstract, introduction,
background, material and methods, results, and conclusion section. Each chapter ends
with a list of references.
The new experiments on strand-to-strand glue lines that extracted the interfacial
properties from double lap shear (DLS) tests using a shear-lag model is addressed in
chapter 2.
Chapter 3 discusses the development of the numerical model by the material point
method (MPM), the development of a simple rule-of-mixtures analysis, and the results of
numerical modeling of tensile modulus. The validation and sensitivity of MPM is
compared to a rule of mixture. Chapter 4 discusses the results of mechanical properties of
wood-strand composites in bending and their comparison to rule of mixtures and beam
theory analysis. The effect of strand length over thickness (slenderness ratio or aspect
ratio) and gaps between strands on mechanical properties is addressed in chapter 5. The
vertical density profile formation during the pressing process is discussed in chapter 6.
Parameters that affect the density profile were also addressed. Chapter 6 also presents 3D
results on density profiles.
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Finally, chapter 7 summarizes the entire research, discusses the conclusions from
the numerical, analytical and experimental work, and considers future research needs.
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References
Bascom, W. D., Yon, K. J., Jensen, R. M., and Cordner L. (1991) “The adhesion of
Carbon
Fibers to Thermoset and Thermoplastic Polymers,”
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