This document discusses the fracture toughness (kic) of polymer-ceramic composite materials, measured through 3-point bending tests, revealing that toughness peaked at 20 wt.% fillers. Analysis showed that micro-cracks coalesced into larger cracks along the interfaces of epoxy and alumina particles. Future research will explore different filler fractions and sizes to further understand their impact on fracture mechanics.

1. Results
(a) (b)
(c) (d)
• In the 3-point bend test, as the displacement
increased, the load on the specimens also increased.
• When the cracks were initiated, the slope of the
curves decreased.
• The highest load at which the specimens fully
fractured was the critical force.
• Mode I fracture toughness KIc was calculated
according to the ASTM E399 standard:
𝐾𝐼𝑐 =
𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝑓𝑜𝑟𝑐𝑒 ∗ 𝑠𝑝𝑎𝑛 ∗𝑓(
𝑎
𝑊
)
𝑏𝑊1.5
f(
𝑎
𝑊
) =
3
𝑎
𝑊
(1.99−
𝑎
𝑊
(2.15−3.93
𝑎
𝑊
+2.7 (
𝑎
𝑊
)2)
2(1+2
𝑎
𝑊
)(1−
𝑎
𝑊
)2
where a is the notch length, b is the breadth, and W
stands for the height of the specimen.
• The fracture toughness of all specimens was in the
range of about 1.5 to 2.5 MPa m.
• Fracture toughness increased as the weight
percentage increased from 10% to 20%, and then
reduced as the weight percent kept increasing.
• Fracture paths were revealed by micro X-ray
computed tomography (micro-CT) images.
• The specimens were numerically rendered as
transparent to reveal the crack.
• The cracks (gold) occurred in front of the notch
(purple) and went into the specimens.
• Several smaller micro-cracks coalesced into
bigger cracks and propagated away from the
notch (Figure 7(a)).
• They went through the alumina particles and
the epoxy matrix and sometimes along the
matrix-particle interfaces (Figure 7(b-d)).
• The deflection of the crack path is also observed
in some slices (Figure 7(c)).
Figure 5. Typical Load-Displacement Curves of 3-point Bend Test for
Specimens with Different Weight Fractions
Figure 6. 𝐊 𝐈𝐜 v.s. Weight Percentage/Volume Percentage of the Particles
Figure 7. (a) 3-D Reconstruction of Fracture Paths and (b) to (d)
Representative slices of Micro-CT Images
Fracture Toughness of Particulate Polymer-ceramic Composites
• Composite materials are widely used in various fields for
their high strength- and stiffness-to-weight ratios.
• Understanding the mechanical behaviors of composites is
important to advance the design of these materials.
• This study focuses on the fracture toughness (KIc) of
polymer-ceramic composite materials.
Introduction
Authors: Ruyi Man1
, Jiacheng Gao1
, Abhinit Kothari1
, Kangning Su1
Supervisors: Jing Du1
, Michael Hillman2
1 Department of Mechanical and Nuclear Engineering, Pennsylvania State University
2 Department of Civil and Environmental Engineering, Pennsylvania State University
Acknowledgments
• David and Shirley Wormley Excellence Fund for the Support
of World Class Engineers;
• Student Research and Engagement Office, Penn State College
of Engineering;
• National Science Foundation Award #1826221.
Future Works
• Specimens with other filler fractions will be made and
tested to further explore the relationship between the
fracture toughness and filler fractions.
• Specimens with different filler sizes will also be made and
tested to explore the effects of filler size on the fracture
toughness.
• In situ 3-point bend coupled with micro-CT will be
performed to reveal the 3D fracture mechanisms in the
fracture processes.
• The data will be incorporated to numerical models to better
understand the mechanical behaviors of the composites and
to better design the composite.
Materials and Method
• Fracture toughness (KIc) values were measured using 3-point
bending test in an Instron Electro E3000 Static/Fatigue Tester.
• All tests were conducted following ASTM E399.
Figure 1. Silicone Mold
Figure 3. Instron Tester Figure 4. A Closer Look At the 3-
point Bend Test
Figure 2. Composite Specimens
Summary
• Composite specimens were made by mixing epoxy and
alumina particle fillers of various weight fractions from 10%
to 60%.
• Three-point bending tests were conducted in order to find
out the fracture toughness of the specimens.
• Highest fracture toughness was measured for specimens
with 20 wt.% fillers.
• Several different fracture paths were revealed using micro-CT
scans.
References
• ASTM E399 standard
• Fu et al. Composites Part B: Engineering 39.6 (2008): 933-961.
• Du et al. Journal of the Mechanical Behavior of Biomedical
Materials 46 (2015): 41-48.
• Du et al. Acta Biomaterialia, 9.2 (2013): 5273-9.
• Epoxy resin was mixed with alumina particles grit size 180
(~76 microns).
• Composite of different volume fractions were cured in
rectangular silicone molds.
• Single edge notched bending (SENB) specimens (5 mm × 5
mm × 25 mm) were made by cutting using a diamond saw
and polishing.
Weight Fraction
Notch
Cracks
Specimen
Notch
100 µm
(MPam)