Niaz Abdolrahim

• PhD
• Professor (Assistant) at University of Rochester

Patterning is a familiar approach for imparting novel functionalities to free surfaces. We extend the patterning paradigm to interfaces between crystalline solids. Many interfaces have non-uniform internal structures comprised of misfit dislocations, which in turn govern interface properties. We develop and validate a computational strategy for des...

Nanoporous gold (NP-Au) exhibits microscale plasticity, but macroscopically fails in a relatively brittle manner. This current study suggests that a core-shell structure can increase both ductility and strength of NP-Au. A core Au foam structure was created using conventional dealloying methods with average ligament size of 60 nm. Nickel was then e...

Using molecular dynamics simulations, the deformation behavior of two types of nanocomposite metallic materials (nano-layered thin films and composite nanowires) is investigated and compared with that of the bulk materials. The first structure is a hybrid nano-layered metallic composite formed by alternating layers of Cu, Ni, Cu, and Nb layers. The...

Nanostructured metallic material (NMM) composites are a new class of materials that exhibit high structural stability, mechanical strength, high ductility, toughness and resistance to fracture and fatigue; these properties suggest that these materials can play a leading role in the future micromechanical devices. However, before those materials are...

In current in situ X-ray diffraction (XRD) techniques, data generation surpasses human analytical capabilities, potentially leading to the loss of insights. Automated techniques require human intervention, and lack the performance and adaptability required for material exploration. Given the critical need for high-throughput automated XRD pattern a...

The high permeability and strong selectivity of nanoporous silicon nitride (NPN) membranes make them attractive in a broad range of applications. Despite their growing use, the strength of NPN membranes needs to be improved for further extending their biomedical applications. In this work, we implement a deep learning framework to design NPN membra...

Current in-situ X-ray diffraction (XRD) techniques generate data over human analytical capabilities – leading to the loss of novel insights. Automated techniques require human intervention, and lack the performance and adaptability needed for material exploration. With the critical need for high-throughput automated XRD pattern analysis of novel ma...

It is well-established that mechanical behavior of the materials is significantly affected under irradiation. This is often due to the growth of nanobubbles that changes the microstructure of the irradiated materials. In this work, growth of helium nanobubbles with different sizes and helium to vacancy (He/V) ratios in copper is investigated using...

We present a framework based on non-equilibrium molecular dynamics (NEMD) to reproduce the phase transformation event of Aluminum under ramp compression loading. The simulated stress-density response, virtual x-ray diffraction patterns, and structure analysis are compared against the previously observed experimental laser-driven ramp compression in...

Formation of vitreous ice during rapid compression of water at room temperature is important for biology and the study of biological systems. Here, we show that Raman spectra of rapidly compressed water at greater than 1 GPa at room temperature exhibits the signature of high-density amorphous ice, whereas the X-ray diffraction (XRD) pattern is domi...

The nanoscale thickness and high porosity of amorphous nanoporous silicon nitride (aNPN) membranes make them useful components in diverse biomedical applications. However, mechanical properties including low plastic deformability and strength of aNPN place significant limits on those applications. Thus, understanding how the microstructure of aNPNs...

In this study, a 3-D convolutional neural network (CNN) is designed and trained with simulated NP materials to investigate their structure-property relationship. It is demonstrated that our approach is able to predict the effective stiffness of NP structure with a wide range of microstructures while exhibiting high accuracy and low computational co...

Identifying structure phase transformation path is essential but challenging in plastic deformation under high-pressure high-strain rate experiments. In this paper, we adopt a framework based on non-equilibrium molecular dynamics and virtual diffraction to reproduce the phase transformation event observed in laser-driven ramp compression. Our simul...

Inspired by the development of strong and ductile composite and gradient materials over the past decade, here we report the investigation of a graded nanoporous (NP) structure utilizing molecular dynamics simulations. The structure is generated by inducing a gradient scaling parameter in a Gaussian random field model. It has a large ligament/pore s...

The mechanical properties, particularly, yield strength and ductility of metals, exposed under irradiation usually degrade due to generation of primary and secondary defects such as dislocations, vacancies, gas-bubbles, etc. Using atomistic simulations, we have shown that irradiation-induced Helium gas-bubbles are not always detrimental and can con...

We use Molecular Dynamics simulations to study mechanical behaviors of crystalline silicon nitride nanoporous membranes with different pore distribution upon tensile loading along the armchair direction. Our results suggest that the proper introduction of the pores in nanoporous membranes leads to the transition from brittle failure into ductile fa...

Mechanism of coarsening and deformation behavior of nanoporous Cu with varying relative density - Lijie He, Muhammad Hadi, Haomin Liu, Niaz Abdolrahim

We use atomistic simulations to investigate the mechanical behavior as well as the structural changes of single crystalline β-Si3N4 nanomembrane upon tensile loading. Our results suggest that upon loading along [ 1¯21¯0 ], the nanomembrane exhibits two distinct elastic behavior with varying Young’s modulus and almost zero plasticity until fracture....

We have performed systematic molecular dynamics simulations to study the deformation behavior of a single crystal structure and a core-shell [email protected] nanoporous (NP) structure under shock loading for a wide range of shock intensities. Our results suggest that the core-shell structure exhibits less volume compression than the single crystal...

We use molecular dynamics simulations to demonstrate a homogenous two-step structural phase trans-formation in the Molybdenum (Mo) phase of a Mo/Cu bicontinuous intertwined composite during tensile loading. The Mo atoms first transform from a <001>-oriented body-centered cubic structure to a <001>-oriented face-centered cubic structure via the Bain...

We investigate the effect of nodal relaxation on the structure and energy of interfacial dislocation networks predicted by a dislocation-based simulation method. To assess the accuracy of these predictions, we compare them to corresponding atomistic simulations. Two types of interfaces are investigated: pure twist grain boundaries along {110}-type...

Structurally, nanoporous (NP) materials can be regarded as a network of interconnected nanowires. In this study, molecular dynamics simulations are employed to investigate the deformation behavior of individual ligaments and isolated three-fold nodes, which are the two main structural components in NP materials. The shear strain tensor analysis is...

In recent years, studies have shown that Nanoporous (NP) metals deform in a relatively brittle manner under tensile loading. We investigated the mechanical performance of NP structures under tensile loading using atomistic simulations. We compared the stress strain curves for two types of NP structures: a single crystal Cu NP structure and a core–s...

We performed atomistic simulations to study the strengthening effect of He bubbles with different He atom concentrations within single crystal copper matrix. Uniaxial tensile deformation test demonstrated mechanical strengthening and enhanced ductility of single crystal copper hosting such He bubbles containing high-density He atoms. The yield stre...

The mechanism of self-diffusion in the absence of any pre-existing point defects (intrinsic diffusion) along an a/2 〈1 1 0〉 screw dislocation in FCC metals is studied using molecular dynamics simulations. High diffusivity along the dislocation core at elevated temperatures is found to be due to the constriction of partial dislocations, where a vaca...

Self-diffusion along the screw dislocation core in aluminum, nickel, copper and silver in the absence of any pre-existing point defects in the structure is studied using molecular dynamics. Simulation results show that the effect of screw dislocation on enhancing self-diffusion is more remarkable in Al and Ni than in Cu, and no significant enhancem...

Silicon nanomembranes are thin nanoporous films that are frequently used as separation tools for nanoparticles and biological materials. In such applications, increased differential pressure across the nanomembranes directly increases process throughput. Therefore, a predictive tool governing the macroscale failure of the porous thin films is funda...

We present a new method for determining the unique reference state in which the Burgers vectors of misfit dislocations in semicoherent interfaces are defined. Similar to previous work, our method requires cancelation of coherency and dislocation stresses far from the interface as well as consistency of far-field rotations with a prescribed interfac...

In recent years, studies have shown that single crystal metallic nanowires (NWs) can exhibit unique pseudoelastic behavior when their cross-sectional area is smaller than a certain critical value, which is on the order of a few nms. The mechanism responsible for this behavior is the formation of partial dislocations (twinning). In this paper we dem...

Cu-Nb nanoscale metallic multilayers (NMM) exhibit very high strength when their thickness becomes less than 50nm. Incoherent or opaque interfaces play a very significant role in defining the overall behavior of the NMM structures. Due to discontinuity of slip systems, interfaces shear easily and act as barriers for slip transmission between layers...

The deformation mechanisms in Cu-Ni-Cu composite nanowires subjected to uniaxial tensile loading are investigated using molecular-dynamics simulations. We particularly explore the coupled effects of geometry and coherent interface on the tendency of nanowires to deform via twins and show pseudoelastic behavior. It is found that the critical size to...