284
X. Wu and J. A. El-Awady
and Stevens [60] argued that their molecular models were fully flexible (there is no
stiffness of the strands), which allows for a higher packing density of the strands
than in a realistic material, which explained the large strain of failure.
On the other hand, Wu et al. attributed the discrepancies between MD and CGMD simulations with experiments to the frequency at which bonds are checked if
they satisfy the bond breaking criterion or not and the percentage of bonds that are
allowed to break during a given time step in the simulations [101]. They have shown
that with increasing bond breaking percentage and bond checking frequency in the
simulations, a more realistic response is achieved. However, performing the bond
breaking checking every time step adds a significant computational cost in large
simulations [101]. Additionally, at any given time step, if a large number of bonds
that satisfy the bond breaking criteria are all allowed to break, then a large amount
of energy would be instantaneously released into the system leading to an instability
in the simulations [101]. Thus, overcoming these issues is important for predicting
realistic responses of epoxies at high strain levels.
4 Multiscale Simulations of Epoxy Interfacial Properties
The advantages of using a multiscale simulations approach are demonstrated in
predicting epoxy’s interphase dominated properties and performances [52, 70].
Understandably the interphase strength depends on various factors, ranging from
material chemistry in the interphase region to the operating conditions [102–104].
Finite element simulations (FEM) are usually the common method to simulate the
overall material properties of epoxies with interfaces. The elastic-plastic constitutive
formula used in FEM models requires input data not only of the bulk epoxy
but also of the interphase region, and the latter are not commonly available in
experimental measurements. In the following, multiscale simulation studies that
account for the epoxy interphase region are reviewed in two general applications,
nanocomposites/composites and coatings/adhesives.
4.1 Epoxy-Based Composites and the Interphase Region
Advanced polymer matrix composites (PMCs) are usually used for structural applications in aerospace, automotive, and marine industries. An in-depth understanding
of the interphase region is especially crucial for PMC applications because the
polymer matrix transfers load to the reinforcement fibers through these interphase
regions. Most mechanical damage initiates in the interphase region and eventually
leads to failure of the whole material. Thus, the interphase region is typically
considered the weakest link in a PMC structure, and its properties largely determine
the performance and failure of advanced PMCs.
X. Wu and J. A. El-Awady
and Stevens [60] argued that their molecular models were fully flexible (there is no
stiffness of the strands), which allows for a higher packing density of the strands
than in a realistic material, which explained the large strain of failure.
On the other hand, Wu et al. attributed the discrepancies between MD and CGMD simulations with experiments to the frequency at which bonds are checked if
they satisfy the bond breaking criterion or not and the percentage of bonds that are
allowed to break during a given time step in the simulations [101]. They have shown
that with increasing bond breaking percentage and bond checking frequency in the
simulations, a more realistic response is achieved. However, performing the bond
breaking checking every time step adds a significant computational cost in large
simulations [101]. Additionally, at any given time step, if a large number of bonds
that satisfy the bond breaking criteria are all allowed to break, then a large amount
of energy would be instantaneously released into the system leading to an instability
in the simulations [101]. Thus, overcoming these issues is important for predicting
realistic responses of epoxies at high strain levels.
4 Multiscale Simulations of Epoxy Interfacial Properties
The advantages of using a multiscale simulations approach are demonstrated in
predicting epoxy’s interphase dominated properties and performances [52, 70].
Understandably the interphase strength depends on various factors, ranging from
material chemistry in the interphase region to the operating conditions [102–104].
Finite element simulations (FEM) are usually the common method to simulate the
overall material properties of epoxies with interfaces. The elastic-plastic constitutive
formula used in FEM models requires input data not only of the bulk epoxy
but also of the interphase region, and the latter are not commonly available in
experimental measurements. In the following, multiscale simulation studies that
account for the epoxy interphase region are reviewed in two general applications,
nanocomposites/composites and coatings/adhesives.
4.1 Epoxy-Based Composites and the Interphase Region
Advanced polymer matrix composites (PMCs) are usually used for structural applications in aerospace, automotive, and marine industries. An in-depth understanding
of the interphase region is especially crucial for PMC applications because the
polymer matrix transfers load to the reinforcement fibers through these interphase
regions. Most mechanical damage initiates in the interphase region and eventually
leads to failure of the whole material. Thus, the interphase region is typically
considered the weakest link in a PMC structure, and its properties largely determine
the performance and failure of advanced PMCs.