Mixed mode I/II fracture criterion to anticipate cracked composite materials based on a reinforced kinked crack along maximum shear stress path

Sadra Shahsavar,Mahdi Fakoor,Filippo Berto 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.6

In this paper, a fracture criterion for predicting the failure of the cracked composite specimens under mixed mode I/II loading is provided. Various tests performed on composite components reveal that cracks always grow along the fibers in the isotropic media. Using a new material model called reinforcement isotropic solid (RIS) concept, it is possible to extend the isotropic mixed mode fracture criteria into composite materials. In the proposed criterion, maximum shear stress (MSS) theory which is widely used for failure investigation of un-cracked isotropic materials will be extended to composite materials in combination with RIS concept. In the present study, cracks are oriented along the fibers in the isotropic material. It is assumed that at the onset of fracture, crack growth will be in a path where the shear stress has the highest value according to the MSS criterion. Investigating the results of this criterion and comparing with the available experimental data, it is shown that, both the crack propagation path and the moment of crack growth are well predicted. Available mixed mode I/II fracture data of various wood species are used to evaluate and verify the theoretical results.

Application the mechanism-based strain gradient plasticity theory to model the hot deformation behavior of functionally graded steels

Salavati, Hadi,Alizadeh, Yoness,Berto, Filippo Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.4

Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (${\alpha}$), austenite (${\gamma}$), bainite (${\beta}$) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range $1000-1200^{\circ}C$ and strain rate 0.01-1 s-1 and a sound agreement is found.

Application the mechanism-based strain gradient plasticity theory to model the hot deformation behavior of functionally graded steels

Hadi Salavati,Yoness Alizadeh,Filippo Berto 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.4

Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (α), austenite (γ), bainite (β) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range 1000-1200°C and strain rate 0.01-1 s-1 and a sound agreement is found.

Printing orientation influence on tensile strength of PA12 specimens obtained by SLS

Ivana Jevtić,Zorana Golubović,Goran Mladenović,Filippo Berto,Aleksandar Sedmak,Aleksa Milovanović,Miloš Milošević 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

Selective laser sintering (SLS) is one of the additive manufacturing technologies dedicated to the production of high-quality parts with complex geometries. Here, polyamide 12 (PA12) is a commonly used material, for manufacturing parts with sufficient mechanical and thermal properties. In SLS, many manufacturing parameters have an effect on the mechanical properties of final parts. Even the decision regarding the orientation of a part in a powder bed may have a significant effect on the mechanical properties. In this research, the influence of horizontal (H) and vertical (V) printing orientations on the ultimate tensile strength (UTS) of fabricated PA12 specimens are examined. Our research findings show that H specimens exhibit larger deformations and smaller UTS value scatter in comparison with V specimens. Also, worth pointing out is the fact that V-oriented specimens have a higher elastic modulus. One can assume that the sintering process is more effective in V specimens, due to a more uniform laser beam trajectory than in the H specimens’ case.

A Review Study for Creep in Different Nanocomposites

Vahid Monfared,Hamid Reza Bakhsheshi‑Rad,Mahmood Razzaghi,D. Toghraie,Maboud Hekmatifar,Filippo Berto 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.9

This article presents a brief review regarding the creep behavior (CB) of the nanocomposites (NCs)-based materials in recentyears. The creep (C) in solids under high stress (HS) and temperature (T) is one of the processes of interest to researchersin the industry. Investigating the time-dependent plastic deformation (PD) of NCs is vital in modern sciences. The C studywould be crucial for elevated T and high stresses applications. (e.g., turbine blades, spaceships, shuttles, and nozzle guidevanes). In addition, a comparatively detailed review of the C of metal-based NCs, particularly magnesium (Mg) based ones,has been presented. Mg and its alloys have recently fascinated much interest in replacing existing structural materials invarious applications because of their outstanding properties like good damping capability, high specific strength, and goodmachinability. However, their use is limited because of their low Creep resistance at high Ts. Encapsulation of nanoparticles(NPs) is one efficient way to better the creep resistance of Mg-based NCs. Movement of dislocation can be hindered by NPs,which act as barriers to dislocations.

Static and fatigue behavior of 3D printed PLA and PLA reinforced with short carbon fibers

Estera Vălean,Pietro Foti,Seyed Mohammad Javad Razavi,Filippo Berto,Liviu Marșavina 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

Fabrication based on additive manufacturing (AM) process from a threedimensional (3D) model has received significant attention in the last few years. The present paper presents the mechanical characterization of 3D printed specimens based on fused deposition modelling (FDM), which is one of the most commonly used AM methods. Tensile and fatigue tests were performed to characterize the quasi-static mechanical response and to evaluate the fatigue performance of FDM thermoplastic materials, respectively. The materials used to manufacture the specimens were polylactic acid (PLA) and PLA reinforced with short carbon fibers (CF). Good correlations were obtained between fatigue resistance and tensile strength for each type of material. It was also observed that the samples reinforced with CF present both lower tensile and fatigue properties. The poorer properties of PLA-CF specimens could be attributed to several reasons such as higher porosity and poorer adhesion between filament layers compared to the PLA counterparts.