This study presents the peridynamic integrals. They enable the derivation of the peridynamic (nonlocal) form of the strain invariants. Therefore, the peridynamic form of the existing classical strain energy density functions can readily be constructed for linearly elastic and hyperelastic isotropic materials without any calibration. A general form of the force density vector is derived based on the strain energy density function that is expressed in terms of the first invariant of the right Cauchy-Green strain tensor and the Jacobian. In the case of linear elastic response for isotropic materials, the peridynamic force density vector is derived based on the classical form of the strain energy density function for three-and two-dimensional analysis. Also, a new form of the strain energy density function leads to a force density vector similar to that of bond-based peridynamics. Numerical results concern the verification of the peridynamic predictions with these force density vectors by considering a rectangular plate under uniform stretch.The peridynamic (PD) theory was introduced by Silling [1], and later generalized by Silling et al. [2]. The PD equation of motion is an integro-differential equation, and the integrand is free of the spatial derivatives of the displacement field. It permits damage nucleation at multiple damage sites in unspecified locations and its propagation along unguided paths with complex interactions.Conceptually rather simple, the bond-based PD introduced by Silling [1] is free of the assumption of small displacement gradients. However, it does not distinguish between dilatation and distortion. Therefore, it presents only one independent elastic constant; the second elastic constant has a fixed value depending on the analysis dimension. The corresponding strain energy density (SED) function is expressed in terms of the stretch between two material points, and one PD material parameter, referred to as the micro-modulus. This micro-modulus is determined through calibration against the classical SED by considering a simple loading condition, such as isotropic expansion. The determination of the micro-modulus for three-and two-dimensional analysis under plane strain and stress assumptions is described by Gerstle et al. [3]. Later, Bobaru et al. [4] proposed different forms of the micro-modulus function and discussed their effect on convergence of the computations. Recently, Chen et al. [5] presented a constructive approach for selecting the most appropriate kernel function in the bond-based PD equation of motion with respect to its convergence characteristics. The state-based PD introduced by Silling et al. [2] retains the two independent elastic constants such as the Young's modulus and Poisson's ratio. However, the determination of the force density-stretch relation requires an explicit form of the SED function. Silling et al.[2] suggested a SED function for three-dimensional analysis based on the deformation state and force state for a material referred to as a "linear peridynamic solid". T...