1. Introduction
All fiber-reinforced polymer (FRP) composite materials, which have significant potential for a wide range of infrastructure applications, contain thermosetting or thermoplastic resins as well as glass and/or carbon fibers. The load-bearing component of the composite is provided by the fiber network, while the resin aids in load transfer and fiber orientation. The resin regulates the manufacturing process and processing variables. Resins also protect the fabrics from environmental factors such as relative humidity-elevated temperatures and chemical attacks.
Significant research has been conducted on the development of FRP composite materials and their novel applications. Many efforts have yielded materials with improved structural properties. Because of their superior corrosion resistance, excellent thermomechanical properties, and high strength-to-weight ratio, FRP composite materials are being promoted as twenty-first-century materials. In terms of their embodied energy, FRP composite materials are also “greener” than traditional materials such as concrete and steel. The use of FRP composite materials in civil and military infrastructure can improve innovation, productivity, and performance while also providing longer service lives, resulting in lower life-cycle costs. These efforts demonstrate that the use of innovative composite materials and designs have significant potential to reduce infrastructure vulnerability.
The BEM with internal collocation nodes has been used to solve thermo-elastoplastic problems [
1,
2]. However, the BEM’s advantage of ease of data preparation is lost in this scenario. Therefore, several BEM strategies have been proposed. Nowak and Neves [
3] developed the multiple-reciprocity boundary element method, which cannot be used to analyze thermo-elastoplastic materials. The dual-reciprocity BEM was developed to solve thermo-elastoplastic problems with an arbitrary heat source [
4]. Eigenvalue analysis can be carried out using the real-part boundary element approach [
5,
6]. The local boundary element method was used by Sladek and Sladek [
7] to solve elastoplastic problems without internal cells. For elastoplastic difficulties, Ochiai and Kobayashi [
8] presented the triple-reciprocity BEM, which does not require internal cells. This method allows for a very accurate solution to be produced using only fundamental low-order solutions and reduces the requirements for data preparation. Ochiai [
9] applied the triple-reciprocity BEM to solve 2D thermo-elastoplastic problems with an arbitrary distributed heat source [
10] and three-dimensional elastoplastic problems with initial strain formulas [
10]. Recently, Fahmy et al. [
11,
12,
13,
14] developed fractional BEM schemes to solve certain thermoelastic problems.
In this paper, a new BEM strategy is developed to solve three-dimensional thermo-elastoplastic wave propagation problems with an arbitrary distributed heat source. Boundary elements and arbitrary internal points are used in this strategy. For elastoplastic analysis, the initial strain or stress distribution is interpolated using boundary integral equations. Strong singularities in the calculation of stresses at internal sites become weak using this method. The impacts of anisotropy and the fractional-order parameter are examined. The validity and performance of the suggested method for a two-dimensional problem are demonstrated, showing excellent agreement with existing experimental and numerical results.
3. BEM Implementation for the Elastoplastic Field
Now, our purpose is to solve the following boundary integral equation [
1,
2]:
where
,
,
, and
are the free coefficient, initial strain rate, displacement rate, and surface traction rate, respectively. However,
,
, and
are the distance between the observation point and loading point, the boundary, and domain, respectively.
According to [
22], Kelvin’s solution
and
can be written as
The functions
, and
in Equation (21) can be expressed as [
1,
16]
where
denotes the thermal expansion coefficient.
Based on the initial stress formulation, the domain integral in Equation (21) can be written as [
1]
where
The following equations are used for initial stress interpolation [
8,
9]:
The initial stress rate
curvature can be expressed as
in which
M is the number of points
.
On the boundary, the initial stress rate
can be written as
For internal points, the following equation is obtained in the same manner as Equation (34)
For performing the interpolation process, the following equations were employed [
15]:
where
.
From Equations (36) and (37), the following equation is established:
In this method, each initial strain component is interpolated.
Using the Green’s second identity and Equation (37), the following result is obtained [
8,
9]:
Now, using the Green’s theorem and Equations (36) and (37), the initial strain rate
can be expressed as [
7,
8]
where
It is assumed that
is zero. For internal points, the following equation is obtained:
when the boundary is divided into
constant elements and
internal points, then
unknowns must be solved simultaneously.
The function
is defined as
Using Equations (36), (37), and (42) and Green’s second identity, Equation (21) becomes
The Kelvin solutions
and
can be expressed as [
8,
9]
Equation (44) can be expressed using Equations (39), (40), and (45) as follows [
9]:
The function
is described as follows:
The domain integral in (28) can be expressed as
Using Equation (46),
is obtained as
Furthermore, using Equations (47) and (48), the normal derivatives
and
are obtained as
Using the stress–strain relationship,
is obtained as
Moreover, the normal derivatives
and
are given by [
11]
The internal stress is given by [
22]
where
represents the initial stress derived from the initial strain. Additionally,
and
in Equation (36) can be expressed as [
1,
11]
The function
is defined as
Using Green’s theory and Equation (66), Equation (59) can be written as
Using Equation (55) and the relationship between displacement and stress,
is obtained as
Similarly,
and
are obtained as
According to [
17], Equation (67) can be written in the following form:
is calculated using Equation (51) and the displacement–stress relationship as
and
are also obtained as
The first thermal load is , the final thermal load is , and the number of iterations is . Then, the incremental load is .
The following iterative relationship is used to solve the current thermo-elastoplastic problem:
where
, and
are yield stress at
, yield stress at
, strain hardening, and equivalent plastic strain increment, respectively. Based on the von Mises yield criterion, the stresses rate in Equation (72) yields the deviatoric stress tensor
, and the equivalent stress
can be computed as
where
The following Prandtl–Reuss equation is employed to calculate the plastic strain increment
as
where
is a proportionality factor.
The plastic strain increment is calculated using Equation (80).
Equations (36) and (37) are used to interpolate the initial strain rate.
The displacement and traction rates are calculated by Equation (43).
Equation (80) is used to calculate the strain rate.
Equation (77) is used to calculate the initial strain rate until convergence.
4. Numerical Results and Discussion
The proposed BEM method is general because it can be used to deal with a wide range of fractional thermo-elastoplastic problems affecting anisotropic fiber-reinforced polymer composite materials. Additionally, it is simple because only the surface of the domain needs to be discretized.
In our study computations, we employed a fiber-reinforced polymer composite with the following properties:
Young’s modulus , Poisson’s ratio , thermal expansion , yield stress , and strain hardening .
We considered the reinforcing parameters , , and .
The pure anisotropic fiber-reinforced behavior satisfies
where
Additionally, the isotropic behavior satisfies .
As illustrated in
Figure 1, the domain of the considered 3D problem includes 40 boundary nodes and 81 internal nodes. Additionally, we assumed that the wave direction is parallel to the
-axis.
Figure 2 shows the distribution of the stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. It is shown from this figure that the stress
sensitivity decreases and then increases along the
axis. Additionally, it increases as the fractional-order parameter increases. This figure demonstrates that the fractional-order parameter has a significant effect on stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 3 shows the distribution of the stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. It is shown from this figure that the stress
sensitivity decreases and then increases and then decreases again the along
axis. Additionally, it increases as the fractional-order parameter increases. This figure demonstrates that the fractional-order parameter has a significant effect on the stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 4 illustrates the distribution of the stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. It is shown from this figure that the stress
sensitivity decreases and then increases along the
axis. Additionally, it increases as the fractional-order parameter increases. This figure demonstrates that the fractional-order parameter has a significant effect on the stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 5 illustrates the distribution of the stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. It is shown from this figure that the stress
sensitivity decreases and then increases along the
axis. Additionally, it increases as the fractional-order parameter increases. This figure demonstrates that the fractional-order parameter has a significant effect on stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 6 illustrates the distribution of the stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. It can be seen from this figure that the stress
sensitivity increases and then decreases as
increases for different fractional-order parameters. This figure demonstrates that the fractional-order parameter has a significant effect on the stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 7 displays the distribution of stress
sensitivity along the
axis in anisotropic fiber-reinforced polymer composites for various fractional-order values. The stress component
increases and then decreases as
increases. This figure demonstrates that the fractional-order parameter has a significant effect on the stress
sensitivity in anisotropic FRP composites. The stress
sensitivity curves at the upper (
) and lower
) values of the fractional parameter diverge from each other, and they are close to each other at the interface values (
).
Figure 8 explains the distribution of the strain
sensitivity along the
axis, which, in isotropic and anisotropic cases, begins with a negative value. It can be seen from this figure that the distribution of the strain
sensitivity initially increases and then decreases along the
axis. Additionally, it has
in anisotropic cases but
for isotropic cases. This figure demonstrates that the fractional-order parameter has a significant effect on the strain
sensitivity in both isotropic and anisotropic cases. The strain
sensitivity curves at the upper (
) and lower
) values of the fractional parameter are also close to each other, and we notice that they are closer in the isotropic case than in the anisotropic case. It is demonstrated that the strain
sensitivity curves at the interface values diverge from each other, as they are further away in the isotropic case than in the anisotropic case.
Figure 9 illustrates the distribution of the strain
sensitivity along the
axis in the context of isotropic and anisotropic fiber-reinforced polymer composites for various fractional-order values. It can be noticed from this figure that the strain
sensitivity increases as
increases at small
values. Additionally, it has
in anisotropic cases, but it has
in isotropic cases, which are close to the approximate values as
tends to infinity. This figure demonstrates that the fractional-order parameter has an important effect on the strain
sensitivity in both isotropic and anisotropic cases. The strain
sensitivity curves at the upper (
) and lower
) values of the fractional parameter are congruent in both cases. It is demonstrated that the strain
sensitivity curves at the interface values diverge from each other, as they are further away in the anisotropic case than in the isotropic case.
Figure 10 explains the distribution of the strain
sensitivity along the
axis, which starts near zero at
in the context of both isotropic and anisotropic cases. It is noticed that distribution of the strain
sensitivity first decreases then increases as
increases at small
values. Additionally, it has
in isotropic and anisotropic cases.
This figure demonstrates that the fractional-order parameter has a significant effect on the strain sensitivity in both isotropic and anisotropic cases. The strain sensitivity curves at the upper () and lower ) values of the fractional parameter are also close to each other, and we notice that they are closer in the anisotropic case than in the isotropic case. It is demonstrated that the strain sensitivity curves at the interface values diverge from each other, as they are further away in the anisotropic case than in the isotropic case.
Figure 11 depicts the distribution of the strain
sensitivity along the
axis, which starts from zero at
in the context of isotropic and anisotropic cases. It noticed that the strain
sensitivity is increases first and decreases and then increases again was
increases. Additionally, it has
for isotropic cases and
for anisotropic cases. This figure demonstrates that the fractional-order parameter has a significant effect on the strain
sensitivity in both isotropic and anisotropic cases. The strain
sensitivity curves at the upper (
) and lower
) values of the fractional parameter are also close to each other, and we notice that they are closer in the anisotropic case than in the isotropic case. It is demonstrated that the strain
sensitivity curves at the interface values diverge from each other, as they are further away in the anisotropic case than in the isotropic case.
Figure 12 explains the distribution of the strain
sensitivity along the
axis, which starts near zero at
in the context of isotropic and anisotropic fiber-reinforced polymer composites for various fractional-order values. It can be seen from this figure that the distribution of strain
sensitivity initially increases and then decreasing along the
axis. Additionally, it has
in isotropic cases but
in anisotropic cases. This figure demonstrates that the fractional-order parameter has a significant effect on the strain
sensitivity in both isotropic and anisotropic cases. The strain
sensitivity curves at the upper (
) and lower
) values of the fractional parameter are also close to each other, and we notice that they are closer in the anisotropic case than in the isotropic case. It is demonstrated that the strain
sensitivity curves at the interface values diverge from each other, as they are further away in the anisotropic case than in the isotropic case.
Figure 13 depicts the distribution of strain
, which starts from zero at
in the context of isotropic and anisotropic cases. It noticed that the distribution decreases and then increases as
increases at small
values. Additionally, it has
in both isotropic and anisotropic cases. This figure demonstrates that the fractional-order parameter has a significant effect on the strain
sensitivity in both isotropic and anisotropic cases. The strain
sensitivity curves at the upper (
) and lower
) values of the fractional parameter are also close to each other, and we notice that they are closer in the anisotropic case than in the isotropic case. It is demonstrated that the strain
sensitivity curves at the interface values diverge from each other, as they are further away in the anisotropic case than in the isotropic case.
There are no published results that demonstrate the validity and accuracy of the current BEM method strategy. On the other hand, some studies can be thought of as special cases in the context of this current general study. The special case distributions
,
, and
for the considered BEM combined the finite element method/normal mode method (FEM–NMM) of An et al. [
23] and the experimental technique (Exp.) of Solodov et al. [
24] and are shown in
Figure 14,
Figure 15 and
Figure 16 for fractional-order (
) anisotropic fiber-reinforced polymer composites. These results show that the BEM findings are in excellent agreement with those of FEM–NMM [
23] and Exp. [
24]. As a result, the validity of the proposed technique was confirmed.