Peridynamics (PD) is a new nonlocal form of classical continuum mechanics, which is very suitable for investigating material failure. However, the application of classical bond-based PD (BPD) to brittle fracture is restricted because the failure models proposed in BPD mainly describe brittle fracture rather than quasi-brittle fracture. Moreover, the models have a limitation of fixed Poisson's ratio, and the effect of internal length on nonlocal long-range forces cannot be reflected. The present study proposes an improved unibond dual-parameter PD (UDPD) model to overcome the three drawbacks in the damage and fracture analyses of quasi-brittle materials. The conversion formulations of the normal stiffness and tangential stiffness between the elasticity modulus and Poisson's ratio were derived first. Then, a continuous function was introduced in the UDPD model by considering the internal length effect of long-range forces, and the corresponding expressions of the micromodulus functions were deduced. Furthermore, the basic form of the constitutive force function of the UDPD was constructed based on the linear and nonlinear mechanical behaviors of the failure process of quasi-brittle materials, and a corresponding failure criterion was used to evaluate the damage. The validity and accuracy of the proposed model were demonstrated by conducting numerical tests on four specimens, namely, a rectangular plate, double-edge notched concrete specimen, unilaterally notched gray cast iron, and concrete L-specimen panel under quasi-static loading. The model results were compared with those of experiments and numerical studies in the literature. It was found that the proposed model has the same simplicity and stability of the BPD model and can fully capture the nonlinear deformation and progressive failure of quasi-brittle materials with different Poisson's ratios.

近场动力学 (PD) 是经典连续介质力学的一种新的非局部形式，非常适合研究材料失效。然而，经典的基于键的 PD（BPD）在脆性断裂中的应用受到限制，因为 BPD 中提出的失效模型主要描述脆性断裂而不是准脆性断裂。此外，该模型具有固定泊松比的限制，无法反映内部长度对非局部远程力的影响。本研究提出了一种改进的单键双参数 PD (UDPD) 模型，以克服准脆性材料损伤和断裂分析中的三个缺点。首先推导了弹性模量和泊松比之间的法向刚度和切向刚度的转换公式。然后，考虑远程力的内长效应，在UDPD模型中引入连续函数，推导出相应的微模量函数表达式。此外，基于准脆性材料破坏过程的线性和非线性力学行为，构建了UDPD本构力函数的基本形式，并使用相应的破坏准则来评估损伤。通过对矩形板、双边缺口混凝土试样、单边缺口灰口铸铁和混凝土四个试样进行数值试验，证明了该模型的有效性和准确性。此外，基于准脆性材料破坏过程的线性和非线性力学行为，构建了UDPD本构力函数的基本形式，并使用相应的破坏准则来评估损伤。通过对矩形板、双边缺口混凝土试样、单边缺口灰口铸铁和混凝土四个试样进行数值试验，证明了该模型的有效性和准确性。此外，基于准脆性材料破坏过程的线性和非线性力学行为，构建了UDPD本构力函数的基本形式，并使用相应的破坏准则来评估损伤。通过对矩形板、双边缺口混凝土试样、单边缺口灰口铸铁和混凝土四个试样进行数值试验，证明了该模型的有效性和准确性。L -准静态载荷下的试样板。模型结果与文献中的实验和数值研究结果进行了比较。发现所提模型具有与BPD模型相同的简单性和稳定性，可以充分捕捉不同泊松比准脆性材料的非线性变形和渐进破坏。