Cracking the code of crack propagation in rubberlike materials

Date:
August 2, 2021
Source:
Institute of Industrial Science, The University of Tokyo
Summary:
Researchers have developed a simplified mathematical model
(step-loading model, SLM) that unifies two earlier mechanisms
to describe the velocity jump in crack propagation. Through SLM,
they showed that the near-tip mechanical behavior observed from
one analysis is derived from the dynamic glass transition at the
crack tip described in another proposal, thus merging the two
distinct analyses, and demonstrating that the velocity jump occurs
in many materials.



FULL STORY ========================================================================== Understanding the fracture behavior of rubber materials is critical to
various industrial applications, including the improved design of reliable products. A team from Japan has identified the origin of a phenomenon
that occurs when rubber materials under stress rapidly break, and has
shown that this abrupt fracturing occurs in many viscoelastic materials.


==========================================================================
The mechanism of the velocity jump -- a phenomenon in which the initial
slow crack in a strained rubberlike material abruptly and rapidly grows
-- has been a mystery for years despite its importance in the design of
durable materials.

Now, there is evidence to support a new theory to explain this unique
event.

In a study published this month in Physical Review Materials, researchers
from The University of Tokyo Institute of Industrial Science have built a simplified mathematical model that merges two previous analyses to reveal
the stress- strain behavior of rubber materials during breakage, further supporting their theoretical analysis with a series of experimental
studies.

"The velocity jump phenomenon in crack propagation remained unsolved for
more than 30 years," says lead author of the study Atsushi Kubo. "Our step-loading model is designed to replicate the non-monotonic mechanical behavior when the rubber material undergoes this sharp transition in
fracturing near the crack tip. Because it does not have to directly
reproduce the complex crack propagation process, which involves
several phenomena, this allows us to construct a simplified model that successfully exhibits the velocity jump." Through their simplified step-loading model, the researchers showed that the mechanical behavior observed from one analysis approximated the phase transition mechanism described in the other proposal, merging the two distinct analyses.

"For the step-loading model, we used a linear viscoelasticity to mimic
the near-tip mechanical behavior in the material. We also implemented a stepwise function without consideration of the crack geometry to model
the rapidly applied external force at the crack tip," explains Yoshitaka
Umeno, senior author. "This simplification allowed us to achieve a
mechanical model for the crack tip as a 'point mass connected to a
viscoelastic element under step loading'." The research team's combined theoretical and experimental study also showed that the velocity jump phenomenon can be found in other materials.

"Our findings suggest that the velocity jump may occur in general
viscoelastic and polymeric materials, in addition to rubberlike solids. It
is crucial to have this integrated understanding of the mechanism to
stimulate the development of more robust polymer materials that are
critical to many different industries," says Kubo.

========================================================================== Story Source: Materials provided by Institute_of_Industrial_Science,_The_University_of_Tokyo.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Atsushi Kubo, Naoyuki Sakumichi, Yoshihiro Morishita, Ko Okumura,
Katsuhiko Tsunoda, Kenji Urayama, Yoshitaka Umeno. Dynamic
glass transition dramatically accelerates crack propagation in
rubberlike solids. Physical Review Materials, 2021; 5 (7) DOI:
10.1103/ PhysRevMaterials.5.073608 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210802140009.htm

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