MCE Ph.D. Thesis Seminar

New manufacturing techniques, such as 3D printing, allow for greater control over ma-
terial properties and can be used to create custom heterogeneous materials. Heterogeneities
can be leveraged to increase fracture toughness by redistributing the stresses, such as due
to an elastic heterogeneity, or by impeding crack propagation, such as the renucleation at a
material interface or edge of a void. The goal of this research is to study the mechanisms
by which heterogeneities work to make composite materials more resistant to fracture than
either of the individual base materials.
The e ects of interfaces on crack propagation in periodic media are experimentally stud-
ied. By performing comparative experiments on two proposed heterogeneity architectures,
the experiments aim to separate the e ects of elastic deformation caused by heterogeneous
inclusions in a composite from the e ects of passing through an interface during crack prop-
agation. Specimens are manufactured from two polymers using polyjet 3D printing. Energy
release rate for fracture is calculated from load and displacement measurements. The results
of the experiments show good agreement with the theory and variational phase- eld simu-
lations of the material architectures. The e ect of renucleation was measured and observed
to be more substantial than that of the elastic contrast alone. Additionally, the amount of
enhancement was observed to depend on the width of the heterogeneous layers.
The interaction between the cohesive zone and elastic sti ness heterogeneity in the peeling
of an adhesive tape from a rigid substrate is examined experimentally and with nite element
simulations. Observations from an experimental peel test indicate that the cohesive zone
suppresses the e ect of the sti ness heterogeneity. The results of numerical simulations show
that the peel force enhancement depends on the strength of the adhesive and the size of the
cohesive zone.