Influence of grain size distribution on the mechanical behavior of materials in a wide range of strain rates

This work compares the mechanical behavior of alloys with influence of grain siz

Predicting the mechanical properties of ultra-high temperature ceramics

A model for predicting mechanical properties of ultra-high temperature ceramics (UHTC) and composites within a wide temperature range is presented. A model can be useful for predicting the mechanical properties of UHTC composites under dynamic loading and thermal shock. Results of calculations taking into account the dependences nonlinearity of the normalized elastic moduli on homologous temperature T/Tm in the range of 0.2 - 0.62. are presented.. Residual stresses in ZrB2 composites reinforced with particles of refractory borides, carbides and nitrides after selective laser sintering (SLS) or spark plasma sintering (SPS) were predicted. It is shown that the fracture toughness KIC of UHTC increases at the sintering temperature in the range 0.45 – 0.62 T/Tm. The residual stress in the matrix of ceramic composites can differ on a sign due to difference between the thermal expansion coefficients of the matrix and inclusion phases. It is shown that the fracture toughness and the flexural strength of ZrB2 matrix composites can be increased by 25% by the introduction of inclusions of specially selected refractory strengthening phases. Dependence of the normalized strength of composites ZrB2–B4C on the logarithm of normalized strain rate can be described by a power law in the range of strain rates from 10^-3 to 10^6 1/s and temperatures from 295 K to ~1673 K. Results of simulation confirm that the technologies of SLS and SPS can be used for the production of UHTC composites with high values of the specific strength and the fracture toughness

Deformation and damage of Fe-Cr steels in a wide temperature range

The deformation and damage of a high chromium steels in a wide temperature range wa

MECHANICAL RESPONSE OF LAYERED STRUCTURES WITH INTERNAL LAYERS FROM METAMATERIALS EXPOSED TO DYNAMIC LOADINGS

The article presents the results of the analysis of mechanical behavior of mechanical layered structures with metamaterial interlayers under dynamic loading. These structures can be used in lightweight structures for damping dynamic loads in transport and aerospace engineering. Structural elements with layers of the mechanical metamaterials have a low specific mass density and high specific strength characteristics. These multilayer structures have a high specific ability to absorb and dissipate the energy of external dynamic loads too. The results of numerical simulation of the response of multilayer structures to dynamic impacts obtained in this work indicate high specific energy absorption and dissipative properties, which make it possible to weaken the pulse amplitude after passing through the layered system and attenuate of cyclic impacts amplitudes. The results obtained indicate the possibility of creating effective mechanical damping structures of the type under discussion

MODELING OF TITANIUM ALLOYS PLASTIC FLOW IN LINEAR FRICTION WELDING

The article presents the results of the analysis of the plastic flow of titanium alloys in the process of the Linear Friction Welding (LFW). LFW is a high-tech process for joining critical structural elements of aerospace engineering from light and high-temperature alloys. Experimental studies of LFW modes of such alloys are expensive and technically difficult. Numerical simulation was carried out for understanding the physics of the LFW process and the formation laws of a strong welded joint of titanium alloys. Simulation by the SPH method was performed using the LS DYNA software package (ANSYS WB 15.2) and the developed module for the constitutive equation. The new coupled thermomechanical 3D model of LFW process for joining structural elements from alpha and alpha + beta titanium alloys was proposed. It was shown that the formation of a welded joint occurs in a complex and unsteady stress-strain state. In the near-surface layers of the bodies being welded, titanium alloys can be deformed in the mode of severe plastic deformation. A deviation of the symmetry plane of the plastic deformation zone from the initial position of the contact plane of the bodies being welded occurs during a process of LFW. Extrusion of material from the welded joint zone in the transverse direction with respect to the movement of bodies is caused by a pressure gradient and a decrease in the alloy flow stress due to heating. The hcp-bcc phase transition of titanium alloys upon heating in the LFW process necessitates an increase in the cyclic loading time to obtain a welded joint

Pentamode metamaterials under dynamic loading

The field of metamaterials has grown considerably in the last few decades due to the advances in new manufacturing technologies. Metamaterials currently are of interest for a wide variety of applications including damping systems. This work is aimed to evaluate dissipative effect of pentamode metamaterials subjected to dynamic loading. The results of numerical modelling of the mechanical behavior of pentamode metamaterials from alpha titanium alloys are received and compared with available experimental data. The model of inelastic deformation and ductile damage criterion are used to describe the ductility of the unit cell of metamaterials in a wide range of strain rates, temperature and stress triaxiality. A methodology for analyzing the energy dissipation due to inelastic deformation of metamaterials at high strain rates is presented. It is shown that the values of the energy dissipation coefficient during uniaxial dynamic compression of the pentamode metamaterial are 1.5 times higher than for the bulk alloy counterpart

Mechanical Behavior of Nanostructured and Ultrafine-Grained Metal Alloy under Intensive Dynamic Loading

Researches of the last years have allowed to establish that the laws of deformation and fracture of bulk ultrafine-grained (UFG) and coarse-grained (CG) materials are various both in static and in dynamic loading conditions. The influence of average grain size on the yield stress, the tensile strength, and the compression strength was established for metal alloys with a face-centered cubic (FCC), a body-centered cubic (BCC), and a hexagonal close-packed (HCP) structures. The study of the microstructure of the alloys after severe plastic deformation (SPD) by the electron backscatter diffraction (EBSD) technique showed the presence of a bimodal grain size distribution in the UFG alloys. Metal alloys with a bimodal grain size distribution possess a negative strain rate sensitivity of the yield stress and higher ductility at quasi-static strain rates. In this chapter, we will discuss the regularities of deformation at high strain rates, damage, and fracture of ultrafine-grained alloys