Tin-based solder joints are widely used to provide high-density interconnection in microelectronic packaging. Experiments show that under repetitive temperature cycling, subgrains may nucleate in the tin phase, contributing to early degradation. We present numerical simulations on a board-level packaging stack-up during cool-down and under thermal cycling. A crystal plasticity model and thermomechanical anisotropy are utilized to study the deformation of the solder joints. With this model, we can quantify the contributions to the deformation from the joint location versus the result of thermoelastic anisotropy during thermal cycling.

The shock-to-detonation transition in energetic materials is governed by coupled processes at extreme temperatures, pressures, and strain rates spanning Ångstroms to millimeters and femtoseconds to microseconds. Traditional multiscale models fail due to the lack of equilibrium and scale separation across the phenomena involved. We address this grand challenge by directly bridging large-scale molecular dynamics (MD) simulations with continuum finite-element (FE) models using MISTnetX, a convolutional deep neural network. Trained on MD simulations of shock propagation through complex microstructures, MISTnetX captures shock–microstructure interactions, hotspot formation, and the transition to deflagration, supplying critical sub-grid information to FE simulations of mechanics, shocks, thermal transport, and chemistry. Applied to a synthetic but realistic nanostructured plastic-bonded RDX composite, MISTnetX enables parameter-free prediction of the full run-to-detonation transition.

The interaction of a shock wave with microstructural defects leads to energy localization and a sudden increase in local temperature. Due to the small time and length scale of the interaction of the shock with defects, it is computationally expensive to capture simultaneously the mechanics that leads to the high temperature spike and the macroscopic damage. Therefore, we developed a surrogate model to predict the heat rate for a given shock strength to replace the explicit calculation of the defect deformation and the resulting temperature spike. This model is integrated in finite element simulations to predict the effect of the local heat rate on the fracture patterns that develop under shock loading conditions with pressure pulses between 0.33 and 0.98GPa on a octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) particle embedded in a Sylgard matrix. (c) 2026 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Mechanical failure is a marked limitation for plastics used in structural, protective and coating applications. In particular, perforation under high-rate deformation is difficult to mitigate through conventional molecular design1,2. Cross-linking is widely used to improve the thermal and chemical stability of polymers, yet under mechanical deformation, it typically renders materials more brittle, limiting impact resistance and functional lifetime3. Overcoming this fundamental trade-off between stability and toughness remains a central challenge. Here we demonstrate that embedding a small fraction of force-sensitive mechanophores as cross-links into common polymers fundamentally reverses this trade-off, producing materials with substantially enhanced ballistic energy dissipation. At strain rates exceeding 107 s-1, we show that mechanophore-cross-linked networks absorb up to about 115% more energy than conventional thermosets and surpass even their uncross-linked thermoplastic counterparts. We attribute this behaviour to a force- and adiabatic-heating-driven local thermoset-to-thermoplastic transition, in which selective mechanophore scission facilitates viscoplastic deformation at the impact site while preserving network integrity in the surrounding regions. We demonstrate the generality of this strategy in both glassy polystyrene and rubbery styrene-butadiene-styrene triblock copolymers. These results establish mechanophore cross-linking as a design principle for converting commodity polymers into impact-resilient materials and open directions at the intersection of polymer mechanochemistry and extreme-strain-rate material behaviour.

Maintaining the microstructure of energetic materials under specific margins is critical to ensure safety and performance. We investigate microstructural evolution of pentaerythritol tetranitrate thin films during thermal aging using phase-field simulations that integrate physical vapor deposition, grain coarsening, porosity evolution, and anisotropic mechanical response. We generate thin films with initial microstructures via physical vapor deposition simulations, followed by aging at two different temperatures. Our results demonstrate three primary stress-driven mechanisms: (1) void elongation along grain boundaries; (2) grain coarsening; and (3) preferential growth of grains with (110) orientations. Additionally, we find that porosity acts as a drag on grain boundary migration, with higher porosity levels reducing grain coarsening rates. These findings reveal the critical role of stresses and elastic anisotropy in controlling long-term microstructural stability of energetic thin films.

High-strain rate deformation caused by microparticles impacting at high velocities is used to refine the microstructure of metallic materials to the nanocrystalline regime. Under these conditions, metallic targets and particles show a gradient distribution of nanograins, with size increasing away from the impact surface. Some of the mechanisms responsible for the refinement process are still not fully understood. We present finite element simulations of single- crystal and polycrystalline aluminum 20 mu m particles impacting a sapphire substrate at velocities ranging from 50 m/s to 500 m/s. The model includes finite deformation crystal plasticity, a contact algorithm, and an equation of state for high strain rate response. We study the effect of crystal orientation on the restitution coefficient, the permanent deformation of the particle, and grain refinement. The extreme deformation of the particle during the impact results in a high dislocation density and lattice rotation that develop a microstructure with a gradient distribution of grains that are smaller near the impact surface. The size of the new grains scales linearly with the inverse of the average stress in the particle.

While previous studies linked whisker formation to various factors in Sn films, the influence of local grain boundary (GB) characteristics on nucleation mechanisms needed further investigation. This study examines how GB geometry and misorientation changes influence whisker nucleation by combining experimental characterization and crystal plasticity simulations. We establish a comprehensive whisker nucleation model where: (1) GB yielding occurs under local compressive stresses, influenced by GB misorientation; (2) normal displacements accumulate at GBs when shear stresses exceed a threshold; (3) localized grain rotation compensates shape changes; and (4) subgrain formation occurs as rotation intensifies, leading to the formation of new grain boundaries. Our results reveal that GB geometry controls this process by determining normal displacement differences through coefficient of thermal expansion mismatches and dictating whether newly nucleated grains achieve necessary configurations for whisker growth.

The miniaturization of solder bumps in flip-chip packages results in large variability in their microstructure making the prediction of joint lifetime challenging. This is of particular importance in Sn-rich solders due to the anisotropic diffusion behavior of Sn and the presence of fast diffusion pathways, such as grain boundaries and twins that vary from joint to joint.We developed a multi-physics phase-field model to predict the electromigration-enhanced evolution of intermetallic compounds in Cu/Sn system with different grain structures. We present simulations of solder joints with polycrystalline Sn with grains with different orientations to observe the effect of Sn anisotropy and grain boundaries on electromigration failure. The simulations predict Cu depletion in the cathode and the formation and accumulation of intermetallic compounds along Sn grain boundaries dependent on the Sn grain orientation. Additionally, Cu 6 Sn 5 clusters are formed in the Sn matrix when high diffusion rates at the interfaces are considered.

Density Functional Theory (DFT) calculations can determine planar defect energies and slip pathways that are present in ordered intermetallic systems used to strengthen Ni-based superalloys, but analytical models used to evaluate the strengthening effects of these phases often involve significant simplifying assumptions. Instead, Phase Field Dislocation Dynamics (PFDD) is a useful modeling tool that incorporates dislocation interactions with precipitates and slip pathways informed by DFT to determine how precipitate shearing might occur under applied stresses with improved accuracy over previous models. In this work, we apply PFDD to study precipitate shearing in HAYNES (R) 244 (R), a high strength Ni-based superalloy strengthened through a novel Ni2(Cr, Mo, W) phase that has a low symmetry Body Centered Orthorhombic (BCO) crystal structure which complicates analysis of slip pathways. Through our modeling, we show the formation of and evolution of extended dislocations in the matrix and in the precipitates, the interaction of dislocations with the precipitates, and the formation of planar faults in the precipitate. A key aspect of incorporating the DFT determined slip pathway is the influence of the unstable fault energy and the asymmetry of the energy pathway on the strengthening aspect of the precipitate. The resulting critical strengths are compared to analytical models. The size, orientation, particle distance, and calculated slip pathway for the different variants in this system are all shown to have an important effect on the critical stress to shear these precipitates.

Sn-Ag-Cu (SAC) has emerged as one of the most widely accepted lead-free solders used as interconnecting material in electronic packaging. However, these systems still have major reliability problems. During manufacturing, the interfacial reaction of Cu with molten Sn-based solder results in the formation of brittle intermetallic compounds (IMC) that accelerate the degradation of these systems. The evolution of IMC follows during operation due to electromigration (EM), which in addition is responsible for Cu depletion. Both mechanisms are strongly affected by the anisotropic diffusion of Sn resulting in large variability of solders life time prediction. We developed a model to study the formation and evolution of IMC and the diffusion of copper due to EM that includes the impact of Sn crystal orientation on solder failure during fabrication and operation. Our findings show that IMC growth is polarized during electromigration, accelerating at the anode and slowing at the cathode. Similarly, copper depletion is more pronounced at the cathode. The anisotropy of Sn strongly affects the rates of IMC growth and copper depletion during electromigration, shaping solder failure during operation.

We present a mechano-chemical model that couples corrosion, mechanical response, and fracture. The model is used to understand the failure of Cu wires on Al pads in microelectronic packages using a multi-phase field approach. Under high humidity environments, the Cu-rich intermetallic compounds (IMC), Cu9Al4, formed at the interface between Cu and Al, undergo a corrosion degradation process. The IMC expands while undergoing corrosion, inducing stresses that nucleate and propagate cracks along the interface between the Cu-rich IMC and Cu. Furthermore, the volumetric expansion of the IMC may cause damage to the passivation layer and enhance the nucleation of new corrosion pits. We show that the presence of a crack accelerates the corrosion process. The model developed here can be extended to other systems and applications.

As a result of thermal cycling, polycrystalline tin films with a large in-plane grain size relative to film thickness on copper substrates show grain boundary (GB) sliding, creep, yielding, and nucleation of shallow grains that become whiskers. These microstructural changes occur near GBs, with different types of changes for different GBs. To understand these different phenomena, it is important to identify local microstructural changes and signatures of deformation mechanisms on free surfaces as deformation progresses, particularly in how they affect the formation of shallow grains. This study does that by characterizing the evolution of morphological, crystallographic, and curvature changes near GBs in large-grained Sn films during rapid thermal cycling. The observed responses include (1) nucleation of new grains accompanied by local yielding as indicated by slip band formation and grain misorientation changes, (2) GB sliding and diffusion, and (3) localized GB migration, with GB sliding and near-GB rotation occurring earlier than other phenomena. The angles between slip planes and observed slip traces suggested that dislocations moved along activated slip planes to form new GBs. These results on large-grained bicrystal films provide insights into the complex stress relaxation behavior of columnar polycrystalline tin films under the same thermal cycling conditions.

The property, performance, and sensitivity of faceted molecular crystals are hard to determine without understanding the post-shock microstructure. Experimental investigations reveal only a subset of properties that are hard to connect to their observed behavior. Interfaces play a unique and outsized role in modifying properties and responses in materials. A rigorous thermodynamic and kinetic analysis is length-scale and time-scale dependent. In this thesis, we extend first-principles-informed molecular simulations to quantify non-equilibrium properties and responses of faceted molecular crystals. We explore energetic crystals and their oriented surfaces; in particular, we explore surface free energy (SFE) in place of surface energy (SE) as a better descriptor for determining their stability and response. Moreover, molecular crystals are often stabilized using polymeric binders (HTPB) and plasticizers such as DOA. The binders by themselves can modify the response of energetic composites to shock compression but can get delaminated. We calculate the work of adhesion for HTPB along different beta-HMX facets. A delaminated versus fully bonded crystal interface can provide a very different hot spot formation environment. The orientation dependence of thermal and mechanical response using multistate methods along with reactive crack propagation can provide a much better understanding of the safe handling and performance of differently manufactured energetic composites.

We study the effect of the crystalline anisotropy and the relative importance of plasticity and friction on the formation of hot-spots in polycrystalline and single crystal β-HMX when impacted at different weak shock strengths with particle velocities 0.1 km/s and 0.4 km/s. We use a continuum model for large deformations that includes an equation of state, single crystal plasticity, fracture evolution, and heat transport. Our results indicate that plastic dissipation creates heterogeneous temperature fields due to crystal anisotropy. At high shock strengths, the temperature due to frictional heating at crack surfaces becomes the critical hot-spot formation mechanism for the conditions and parameters studied here. Furthermore, the predicted temperature is more sensitive to changes in the friction coefficient than the Taylor–Quinney coefficient accompanying the plastic dissipation used in the thermal transport equation.

This paper demonstrates a novel Eulerian computational framework for modeling anisotropic elastoplastic deformations of organic crystalline energetic materials (EM) under shocks. While Eulerian formulations are advantageous for handling large deformations, constitutive laws in such formulations have been limited to isotropic elastoplastic models, which may not fully capture the shock response of crystalline EM. The present Eulerian framework for high-strain rates, large deformation material dynamics of EM incorporates anisotropic isochoric elasticity via a hypo-elastic constitutive law and visco-plastic single-crystal models. The calculations are validated against atomistic calculations and experimental data and benchmarked against Lagrangian (finite element) crystal plasticity computations for shock-propagation in a monoclinic organic crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7 tetrazocine (β-HMX). The Cauchy stress components and the resolved shear stresses calculated using the present Eulerian approach are shown to be in good agreement with the Lagrangian computations for different crystal orientations. The Eulerian framework is then used for computations of shock-induced inert void collapse in β-HMX to study the effects of crystal orientations on hotspot formation under different loading intensities. The computations show that the hotspot temperature distributions and the collapse profiles are sensitive to the crystal orientations at lower impact velocities (viz., 500 m/s); when the impact velocity is increased to 1000 m/s, the collapse is predominantly hydrodynamic and the role of anisotropy is modest. The present methodology will be useful to simulate energy localization in shocked porous energetic material microstructures and other situations where large deformations of single and polycrystals govern the thermomechanical response.

Imaging the collapse of a single void that creates a hot spot initiation site in an otherwise defect-free explosive is challenging given the spatial and temporal scales involved in explosive systems. This work presents our attempt to examine a single hot spot mode (void collapse) in single-crystal octahydro-l,3,5,7-tetranitro-l,3,5,7-tetrazocine (HMX) embedded in Sylgard. The hot spot heating mechanisms involved with pore collapse include adiabatic heating, jetting, and viscoplastic dissipation. Quantifying the dynamics of a pore collapse is a crucial step to understanding which mechanisms dominate during ignition events. Our experiments were conducted with a single-stage, light-gas gun at Argonne National Laboratory's Advanced Photon Source, applying the phase contrast imaging technique while collecting high-speed video. The details of HMX single crystal production, defect (pore) engineering, and sample construction, along with experimental results are presented here. These results demonstrate that detailed collapse dynamics can be obtained from homogeneous, single-crystal explosives with this approach. Qualitative comparisons are made with simulation data which show good agreement in the transition between a quasi-symmetric pore collapse and an asymmetric collapse with jetting across the pore as measured with normalized pore area and pore circularity.