The Strength of Inconel 625, Manufactured by the Method of Direct Laser Deposition under Sub-Microsecond Load Duration

This paper presents the results of measurements of the spall strength and elastic-plastic proper-ties, under dynamic and static loads, of the high-strength heat-resistant nickel-chromium alloy Inconel 625, obtained by the direct laser deposition method. The structural parameters of the obtained samples and the mechanical properties during static tests were studied. According to our information, anisotropy in the structural parameters operates primarily at the level of plastic deformation of alloys. Shock compression of the additive alloy Inconel 625 samples in the range of 6–18 GPa was carried out using a light-gas gun, both along and perpendicular to the direction of the deposition. The strength characteristics were determined from the analysis of the shock wave profiles, which were recorded using the VISAR laser velocimeter during the loading of samples. It was found that the value of the spall strength of additive samples does not depend on the direction of deposition, and the Hugoniot elastic limit of samples loaded perpendicular to the deposition direction is about ~10% higher. With an increase in the maximum compression stress, the material’s spall strength increases slightly, but for both types of samples, a slight decrease in the Hugoniot elastic limit was observed as the compression stresses increase. On the basis of the measured wave profiles, shock Hugoniots of the samples of the alloy Inconel 625, loaded both along and perpendicular to the direction of deposition, are constructed in this pressure range.

Spallation Characteristics of Single Crystal Aluminum with Copper Nanoparticles Based on Atomistic Simulations

In this study, the effects of Cu nanoparticle inclusion on the dynamic responses of single crystal Al during shockwave loading and subsequent spallation processes have been explored by molecular dynamics simulations. At specific impact velocities, the ideal single crystal Al will not produce dislocation and stacking fault structure during shock compression, while Cu inclusion in an Al–Cu nanocomposite will lead to the formation of a regular stacking fault structure. The significant difference of a shock-induced microstructure makes the spall strength of the Al–Cu nanocomposite lower than that of ideal single crystal Al at these specific impact velocities. The analysis of the damage evolution process shows that when piston velocity up ≤ 2.0 km/s, due to the dense defects and high potential energy at the interface between inclusions and matrix, voids will nucleate preferentially at the inclusion interface, and then grow along the interface at a rate of five times faster than other voids in the Al matrix. When up ≥ 2.5 km/s, the Al matrix will shock melt or unloading melt, and micro-spallation occurs; Cu inclusions have no effect on spallation strength, but when Cu inclusions and the Al matrix are not fully diffused, the voids tend to grow and coalescence along the inclusion interface to form a large void.

High-Strain Deformation and Spallation Strength of 09CrNi2MoCu Steel Obtained by Direct Laser Deposition

In this work, the critical fracture stresses during spalling of high-strength steel 09CrNi2MoCu samples obtained by direct laser deposition (DLD) were measured under shock compression of up to ~5.5 GPa. The microstructure and mechanical properties of DLD steel samples in the initial state and after heat treatment were studied and compared to traditional hot rolled one. The microstructural features of steel before and after heat treatment were revealed. The heat treatment modes of the deposit specimens on their strength properties under both static and dynamic loads have been investigated. The spall strength of the deposited specimens is somewhat lower than the strength of steel specimens after hot rolling regardless of their heat treatment. The minimum elastic limit of elasticity is exhibited by the deposit specimens. After heat treatment of the deposit samples, the elastic limit increases and approximately doubles. Subsequent heat treatment in the form of hardening and tempering allows obtaining strength properties under Hugoniot loads in traditional hot-rolled products.

Shock-Wave Properties and Deformation-Induced Structure of Commercial-Purity Titanium

The shock compressive wave profiles of commercial-purity titanium samples under different loading conditions have been measured. The spall strength of titanium as a function of the strain rate and temperature of deformation has been found. High-rate plastic deformation mechanisms have been studied. High-rate plastic deformation under the investigated loading conditions has been shown to occur by slip and twinning. The α → ω transformation has been established to begin at 12.2 GPa.

Microstructural evidence of the toughening mechanisms of polyurethane reinforced with halloysite nanotubes under high strain-rate tensile loading

In this study, we have investigated the relationship between the spherulitic morphology and the dynamic tensile response of polyurethane reinforced with Halloysite nanotubes (HNTs). The polyurethane prepolymer is partially silane end-capped and filled with only 0.8 wt.% of acid-treated Halloysite nanotubes. The resultant nanocomposite material presents a 35% higher spall strength compared to the neat polyurethane and 21% higher fracture toughness. We show evidence that the HNTs are not the toughening phase in the nanocomposite, but rather it is their influence on the resultant spherulitic structures which alters the polymer microstructure and leads to a tougher dynamic response. Microstructural characterization is performed via Scanning Electron Microscopy, Atomic Force Microscopy and Field Emission Scanning Electron Microscopy, and crystallinity examination via X-ray diffraction. The spherulitic structures present a brittle fracture character, while the interspherulitic regions are more ductile and show large deformation. The nanocomposite presents a finer and more rigid spherulitic structure, and a more energy dissipative fracture mechanism characterized by a rougher fracture surface with highly deformed interspherulitic regions.

Molecular Dynamics Simulations of Shock Propagation and Spallation in Amorphous Polymers

We conducted large-scale molecular dynamics (MD) simulations of shock wave propagation and spallation in amorphous polyurethane and polyurea. First, we computed the shock Hugoniot of the polymers using the multiscale shock technique and compared them with available experimental data to establish the upper limit of the shock pressure that can be accurately modeled using a non-reactive interatomic force field. Subsequently, we simulated shock wave propagation in the polymers, varying the shock particle velocity from 0.125 km/s to 2 km/s. A remarkable similarity in the shock behavior of polyurethane and polyurea was observed. The spall strength of each sample was computed by two methods: (a) the indirect method (based on the free surface velocity history)—accessible in experiments, and (b) a direct method (based on the atomic stresses in the region of spallation)—accessible only through MD. The results reveal that the tensile strength computed from the indirect method is consistently smaller than the value obtained from the direct method. Moreover, the strength computed from the indirect method shows a noticeable agreement with the fracture nucleation stress. Our results provide novel molecular-level insights into the spallation mechanisms of amorphous polymers, which could facilitate the design of polymers for structural barrier applications.