## 1 Introduction
They have also presented a polycarbonate constitutive model embracing a stress-strain/force-deformation relationship. [PERSON] and [PERSON] and [PERSON] (2018) developed a constitutive model and fracture criteria that can be implemented in finite element software. They used this model to accurately simulate the fracture of blunted and sharp PC specimen subjected to four-point bending loading. The demand for reliable and economical solar energy solutions is thriving. Solar power is harvested in three forms: (i) electrical power using photovoltaic (PV) modules, which convert solar irradiation directly into electricity, (ii) thermal power flat absorption, and (iii) concentrated thermal power using reflection by using mirrors that concentrate solar power locally (linear absorber in parabolic trough, or a point absorber in parabolic dish) or remotely at a central tower. The solar-thermal system is typically used for electricity generation using pressurized steam. In all of these methods, steering PV cells, and solar reflecting elements increases the solar power generation. Steering is necessary for solar towers and parabolic dishes. For heliostats in solar towers, dual axis orientation control is employed for steering. Thus, a certain amount of energy is consumed on this controlled movement. Employment of lightweight materials such as polycarbonate in the manufacturing and packaging of the steered elements shall require small driving forces, which reduce the power needed for steering. Concentrated solar thermal or photovoltaics require curved surfaces: parabolic troughs or parabolic dishes. Typical silvered glass mirrors have excellent reflectivity and longevity. However, curving glass surfaces is much more difficult compared to curving metallic or plastic surfaces. Thermoforming of plastic materials like polycarbonate is a mature technology [PERSON] et al. (2018). Moreover, plastics are lightweight materials, which is advantageous for transportation and installation. Unlike glass, plastics are generally more resistant to damage [PERSON] et al. (2018). However, polycarbonate is not a reflective material. Therefore, reflection can be achieved by adding a reflective thin layer. Plastic surfaces must be treated for proper adhesion of the reflective film. [PERSON] et al., have developed and tested sputtering method to apply reflective aluminum film to a polycarbonate film followed with a protective resin layer [PERSON] et al. (2018). Still, the presence of notches in structural components is inevitable. For example, cuts and/or holes might be required for the solar surfaces to be fixed to the steering support. Therefore, having an effective engineering design tool capable of estimating the fracture load of notched polycarbonate members is necessary for ensuring the structural integrity of these members. As mentioned earlier, continuum-mechanics based constitutive models describing the mechanical behaviors of PC were developed [8; 11; 12; 13; 16; 18; 19]. However, such models require extensive computational effort. Engineering design models such as the strain energy density (SED) [23] and the theory of critical distance (TCD) [24] have been successfully used to analyze the failure of notched members with different notch geometries and materials, and under both static and cyclic loading [25; 26; 27; 28; 29]. A key advantage of these models is that they do not require elastic-plastic or complex computational analyses and yet provide accurate predictions. In 2012, [PERSON] [30] proposed the so-called equivalent material concept (EMC) to equate an actual ductile material with a virtual brittle-type material. In principle, the total strain energy density represented by the area under the true stress-strain curve is equated to that of the virtual brittle material. Based on the EMC, the modulus of elasticity, the Poisson's ratio and the fracture toughness of the virtual material are assumed to be the same as for ductile material. Essentially, the EMC is used to determine the fracture stress of the virtual material.