| Based on the two unique superiorities of multi-crack cracking and strain hardening,engineering cementitious composites(ECC)have attracted the attention of researchers from various aspects.Compared with concrete materials,both the removal of coarse aggregates and the addition of fibers make ECC have superior ductility.This material is also more used in tensile members or structures.When the ECC material is made as a beam structure,due to the adhesion between the fiber and the matrix under tension and the very weak fiber force under compressive stress,the fibers in the compression zone can't fully play their due role,but also waste fibers and result in increased costs.Therefore,in order to save fiber consumption and reduce cost,we proposed a functionally graded ECC structure and then discuss its dynamic fracture performance.Peridynamics is a non-local theory.Compared with traditional numerical analysis methods such as finite elements,it has a greater advantage in solving discontinuity questions.For problems such as initial cracks and void defects,the theory can also give accurate answers.ECC is a fiber-reinforced composite material.In this paper,the corresponding PD theoretical model is constructed for this composite material,and two familiar modeling methods are introduced: fully discrete and semi-discrete.Based on the consideration of computing efficiency and accuracy,finally,semi-discrete theory,which consider fiber/matrix interactions,as a theoretical support to study the fracture properties of composites.Also,taking into account the softening characteristics of the cement matrix material,the damage coefficient of bond is introduced to accurately simulate the behaviors.In addition,in order to verify the rationality of the PD model of the composite structure,corresponding simulations were carried out according to the experimental conditions,and the simulation results were approximately consistent with the forms of crack propagation in experiment.In this paper,the semi-discrete PD model of composite materials is applied to simulate the fracture behavior of the ECC structure with initial defects,and the research content and conclusions are summarized as follows:(1)Before applying this theory,we take a cement substrate with dimensions of 100 mm × 40 mm as an example,the results under two convergence factors(m and ?)were simulated and compared.According to the stability trend of the simulation results and the calculated time cost,a reasonable near-field value is obtained,that is,m = 4,and ? = 1.6 mm;(2)Taking the two-dimensional FGECC cantilever plate as the structural model,the influence of the existence of the notch on the cracking and crack propagation of the specimen under the transverse tensile effect was studied,and two types of single notch and symmetrical notch on the edge were considered.Conclusion shows that when the notch exists in the layer with the largest fiber content,the notch has a greater influence on the cracking of the specimen and has a higher sensitivity,whereas the contrary has a weaker effect and a lower sensitivity.In addition,for specimens with symmetrical notches on the edges,the greater the gradient of the fiber content,the more the precracks are concentrated in the fiber-free layer.In addition,a sufficient amount of fibers are also a prerequisite for ensuring multiple cracks;(3)When the cantilever structure is used as the beam body,a proper amount of fiber content can prevent the overall failure of the structure in a short time,that is,the local fracture phenomenon.In addition,the gradient of the fiber content can not only make full use of the fibers,but also delay the cracking speed of cracks.When the cantilever structure is under tensile load,the existence of micro-notches is not the main factor affecting the cracking of the specimen.The area is often the area where the specimen is severely damaged,which is mainly manifested as localized fine cracks. |
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