Composite materials are widely used refer to their exceptional mechanical character-istics, including; impressive tensile strength, high strength-to-weight ratio, superior re-sistance to damage, and better stiffness [1]. Epoxy resin is a class of polymer hermos-set that exhibits remarkable adhesive abilities and mechanical toughness for a wide range of applications in industry. Their ability to be compatible with numerous reinforcement ma-terials allows for substantial design flexibility. This makes it beneficial in advanced epoxy-based composite materials used in industries such as aerospace, automotive, structural engineering, and electronics. Therefore, these composites provide superior performance and exceptional durability. Thus, becoming an essential component in modern production [2,3].

Fiber-reinforced polymer composites are superior to traditional composites in terms of efficiency since fiber reinforcement gives the final product dimensional stability. These composites provide plenty of benefits, including flexibility, ease of installation, and an ex-tended life of service. There are numerous forms and types of fibers reachable, aramid fiber (Kevlar) is particularly remarkable due to its effect on strength, stiffness, and other essential characteristics [4,5,6].

Kevlar fiber is getting recognition for its excellent mechanical properties, compared with glass and carbon fiber it enhances impact resistance, and Kevlar exhibits a superior ability to withstand fracture and reduce impact load [7]. Several researchers have exam-ined fiber characteristics under creep behavior scenarios. Vasudevan et al. [8] investigate the influence of stacking sequences on the mechanical characteristics of Kevlar/glass fiber and carbon/glass fiber composite. Through their observation, they found that enforcement of this synthetic fiber into the fiber composites resulted in a 7.5% enhancement in absorp-tion energy. Sahu et al. [9] illustrated the effects of hybridization on the mechanical characteristics of Kevlar, glass, and carbon fibers hybrid composites via both experimental and numerical simulation. The finding shows a good correlation between the experiment and numerical results. Asit Behera et. Al. [10] fabricated the effect of moisture on the mechanical characteristic of Kevlar fiber-reinforced epoxy composite. Using hand lay-up technique, by immersion in three different types of solutions. They revealed that compo-site-absorbed moisture decreases tensile and breaking strength significantly. Almeida Jr. et. Al. [11] studied the creep characteristics of carbon fibers reinforced epoxy composite with different fiber orientations. By employing both [Findley’s and Burger’s models] to predict the creep behavior of carbon fibers reinforced epoxy composite, experimental data is then utilized to validate analytical results. Ali A. Battawi and Balsam H. Abed [12] examined the creep behavior of natural fibers (fish scales and chicken feathers) as a suitable reinforcement in polyester composite, with different weight fractions of natural fiber employing the hand lay-up method. In comparison with pure polyester, results reveal encouraging characteristics, as it increases creep strain to 74.2% and reduces creep stress to 40.71%. experimental, numerical, and theoretical results were compared with an average deviation of no more than 3.2%. Ali A. Battawi and Balsam H. Abed [13] explored the effects of adding two types of natural fiber sheep wool and horse hair as a reinforcement agent of polyester composite to improve mechanical properties in terms of creep behavior. ANSYS Mechanical APDL was implemented to verify experimental and theoretical results. Balsam H. Abed and Ali A. Battawi [14] studied the creep characteristics of polyester/polystyrene composites reinforced with a weight ratio of fish scales at constant load and temperature. The Maxwell technique was used to determine stress and modulus of elasticity from the (strain/time) curve, by employing curve fitting techniques. Creep characteristics, stress, and modulus of elasticity are studied experimentally. Balsam H. Abed et. Al. [15] evaluated how immersion media affect the creep behavior of polyester compo-site material reinforced with fillers derived from chicken feathers. Creep samples were made by varying weight ratios and immersed in three separate mediums. The results show that composite samples show enhancing creep characteristics due to the immersions. Balsam H. Abed et. Al. [16] investigated the creep behavior of epoxy composite with several weight ratios of Yttrium powder. The composite creep samples were subjected to five distinct loads at constant temperatures. Both numerical and experimental evaluations were conducted to assess creep behavior, Young’s modulus, and stress of the composites. Yang et. al. [17] researched the creep behavior Of epoxy composite tubes in flexural loading using an experimental analysis, creep test was conducted at various stress values from (45 – 75 %) of the flexural ultimate strength at constant temperature and time. The mechanical efficiency, deformation, and reliability of the tubes were evaluated using superposition techniques. Kaveh Rahmani et. Al. [18] Examined the corrosion and creep characteristics of an epoxy-based composite material reinforced with Kevlar, carbon, and glass fibers. Results revealed that carbon fiber had the highest creep resistance in comparison with Kevlar and glass fibers, in contrast, Kevlar fiber exhibits the lowest corrosion risk among the three types of fibers. Madhu Bharadwaj et. Al. [19] proposed a mathematical model to convert the Burger model into the Prony series by using the ANSYS program. Therefore, the model can depict the entire time-dependent creep behavior. A significant similarity between the data gathered experimentally and the data obtained via ANSYS software. The creep phenomenon in Visco-elastic material can be divided into three categories: (primary, secondary, and tertiary). Creep refers to the material elongation with time, usually occur-ring at high temperatures, while some materials exhibit creep at low temperatures or room temperature. In the primary stage, the material exposed high deformation which slowed down eventually. The creep curve is affected by the material, time, and load. While in the second stage, the material deformation is relatively constant. Finally, in the tertiary stage, a high rate of deformation will occur rapidly leading to material failure.

Most engineering practices focus on the primary and secondary stages, hence in practical applications high deformation seen in the tertiary stage was rarely experienced [20] Figure 1 shows the three stages of creep behavior.

In essence, Visco-elastic models can used to describe the elastic and viscos of polymeric material. Hence the term (visco-elastic) demonstrates both elastic and viscos models. In the present study employed These models as a useful estimation for understanding the time-dependent behavior of polymers. To generate these models, simple linear component spring and dash-pot are combined in parallel or series layout Maxwell, Kelvin-Viogt and Burger models are mathematical models that combine the characteristics of spring and dash-pot to accurately reflect system behavior. Dash-pot viscosities and spring stiffnesses are model parameters, that can be determined through fitting procedures or experimental data. Maxwell model has an elastic spring (E₁) in parallel with vis-cos dash-pot (η₁), and the Kelvin-Viogt model, which features an elastic model (E₂), in parallel with vis-cos dash-pot (η₂) as shown in Figure 7. The fundamental equations for linear elastic and Viscos are presented in equations 1 and 2:

Hence: σ: applied stress, Ԑ: strain, Ԑ ́: strain rate, E: modulus of elasticity and η: Viscosity.

These constants represent the required Burgers model. It intends to model the behavior of creep with constant initial stress (σ₀), by combining these two models, by considering initial, primary, and secondary creep strain with acceptable accuracy as illustrated in Figure 8 shows the schematic representation of Burger’s model. Generally, the fundamental equation of Visco-elastic material is presented in the differential equation form below:

To determine material constants (E₁, E₂, η₁, η₂) experimental data may use in the linear viscoelasticity: where:

r₁ = (P₁-A)/2P₂, r₂ = (P₁+A)/2P₂, A = √(P₁+4P₂), P₁=(η₁/E₁+η₁/E₂+η₂/E₂), P₂=η₁η₂/E₁E₂, q₁=η₁, q₂=η₁η₂/E₂

stress relaxation equation can be presented as: where r₁, r₂, P₁, P₂, A, q₁, q₂ are material constants, this fundamental equation of linear stress (4), strain (5), derivate with time $\dot{\sigma }$, $\ddot{\sigma }$, $\dot{\mathrm{Ԑ}}$, $\ddot{\mathrm{Ԑ}}$

Maxwell and Kelvin-Viogt models are appropriate for theoretical and qualitative assessment, but they frequently struggled to depict accurately the physical behavior of actual material, to improve the realism of these materials, additional springs and dash-pots need to be combined to raise the number of elements involved.

The Burger model shown in Figure 8 is the simplest linear model that accurately describes the behavior of time-dependent Visco-elastic materials. This model combined Maxwell and Kelvin-Viogt models in series. The fundamental equation could be derived by investigating the strain responses under applied load, which represented in equation (6).

(σ_o) initial stress, Ԑ(t) creep strain with time (t), Experimental data from creep test in linear Visco-elasticity can apply to calculate materials constants (E₁, E₂, η₁, η₂).

Because of the intricacy of a mathematical model, few Visco-elasticity problems have a proven analytical solution. Nevertheless, the implementation of numerical simulation and digital technology has had an important effect on this field of study. Finite element analysis is one of the numerical techniques created to face the difficulties of structure analysis consisting of both linear and non-linear Visco-elastic material. Such methods are carried out through specialist application programs made for this purpose such as ANSYS software [22].

Many commercial finite element approaches like ANSYS and ABAQUS do not incorporate the Burger model into their software. However, a more general Visco-elastic model named the Prony series that can be used to represent a wide range of materials. The burgers model may be implemented into this finite element software by modifying the constants of the Prony series appropriately. This process is described in this section, in which the Burgers model is imitated by modifying the Prony series. Literature [19] indicates that a specific approach can be used to transform Burger parameters into Prony coefficients (Ԏ₁, Ԏ₂, g₁, g₂). As a result, the material constant must be presented in ANSYS as follows: where: α, β = (P₁±√(〖P₁〗^2-2P₂))/2P₂

Burger model parameters and Prony series coefficients used in the ANSYS program for different weight ratios of Kevlar and carbon fiber are presented in Table 2.

In this study, the commercial finite element software ANSYS 15.0 was used to confirm the numerical solution. Plane 182 2D solid structure element with four nodes and two degrees of freedom commonly used in the ANSYS program, was performed to model a finite element analysis of the creep test sample utilized in this simulation. AutoCAD software was used to create a Two-dimensional creep sample, then exported to ANSYS to simulate the behavior of creep for an epoxy composite sample reinforced with two types of filler in different weight ratios. Figure 9 depicts a two-dimension finite elements design of a creep test sample.

Sika epoxy composite conducted to mechanical test prior to and after adding fiber reinforcement to assess the effects addition of fibers on the mechanical characteristics of the materials.

In this study, the creep behavior of sika epoxy composite reinforced with carbon fiber and Kevlar fiber was investigated. The result of the creep test revealed that improved creep compliance correlated with high weight fraction, this suggests that weight percentage is essential for determining the mechanical characteristics of the materials. Fiber type is cruel, Kevlar fiber possesses the lowest creep strain and low-stress level than carbon fibers. Hence Kevlar fibers are stronger and have greater resistance to creep. Consequently, it’s strongly recommended. The results proved that the theoretical results obtained using the Burger method fit closely with the Prony series utilized in numerical simulation ANSYS 15.0 program results both had potential for accurate prediction of experimental findings.

The significant improvement of mechanical characteristics, especially creep strength, by the inclusion of carbon and Kevlar fibers with weight fractions up to 5%, offers an important chance for incorporating these material composites in the arrangement of mechanical applications. Especially for lightweight components. This could permit it to be utilized as an alternative to iron or metal parts.