Additive manufacturing (AM) metals such as powder bed-fused and laser-sintered titanium alloys, i.e., PBF-LS/ Ti6Al4V, have attracted considerable attention in recent times. However, their fatigue strength is almost half that of wrought materials, thereby limiting their practical applications. The primary reason for the weak fatigue strength is the presence of surface defects as deep as 0.15 mm due to incompletely melted particles during PBFLS. In this study, to demonstrate the improvement of the fatigue strength of PBF-LS/Ti6Al4V by post-processing, as-built PBF-LS/Ti6Al4V was treated by fine particle bombarding (FPB) with garnet to remove the surface defects, followed by cavitation peening (CP), which introduced compressive residual stress. The fatigue properties of the treated specimen were evaluated through torsional fatigue tests and compared with those of hot-rolled Ti6Al4V and specimens treated using other post-processing methods such as submerged laser peening (SLP). According to the results, at Nf = 107, FPB + CP-treated PBF-LS/Ti6Al4V exhibited a fatigue strength of 446 +/- 5 MPa, whereas as-built PBF-LS/Ti6Al4V and hot-rolled Ti6Al4V exhibited fatigue strengths of 210 +/- 10 and 347 +/- 26 MPa, respectively. The fatigue strength of as-built PBF-LS/Ti6Al4V was enhanced by the combination of FPB and CP, and the improved fatigue strength was greater than that of hot-rolling.

Understanding microscopic damage mechanics in laminated CFRP at high-strain-rate (HSR) loading and extreme temperatures remains an enduring challenge. Using X-ray tomography coupled with digital volume correlation (DVC), three-dimensional local displacement/strain fields and segmented micron-scale intra-ply cracking were quantified, revealing damage micro-mechanics at HSR. Local deformation exhibits strong directionality that intensifies with increasing strain and decreasing temperature, accompanied by earlier and more rapid damage development at low temperature. Strain-damage correspondence indicates both Mode-II-dominated and mixed-mode (I/II) intra-ply cracking, while delamination shows a stronger Mode-I contribution but remains mixed-mode. Inter-ply kinematic constraint and shear transfer between adjacent plies with mismatched fibre orientations were directly visualised and characterised under HSR loading, particularly at low temperature. Together with the spatially non-uniform and asynchronous development of local deformation through the laminate thickness, these results highlight substantial departures from the nominal in-plane shear state commonly assumed for uniaxial +/- 45 degrees laminate tests under extreme conditions.

Understanding the evolution of damage in aerospace-grade CFRP composites after high-speed impact events is crucial for the safe design of components that can withstand dynamic loads. In this study, the temperature-dependent mechanisms of micro-scale damage in angle-ply CFRP were studied through a combination of interrupted high-rate compression experiments and synchrotron X-ray phase-contrast micro-tomography employing deep-learning-aided image analysis. Despite the earlier damage onset at low temperatures, all specimens tested have similar apparent-yield strains. The mechanisms responsible for the early damage, namely mode-II-dominant fracture in surface and subsurface plies, are observed to be similar at both low and room temperature, with the surface ply cracks the first to develop into opened damage. After the occurrence of the middle-ply opened damage, while the room-temperature specimens dissipate energy through deformation and cracking originating from the specimen loading ends, glassy inter-ply fractures propagating from the surface towards the middle plies are the root of the rapid drop in specimen strength at low temperatures after the apparent-yield point.

This paper investigates the potential of VMamba, a state-of-the-art vision backbone, for enhancing displacement field measurement between speckle image pairs, resembling the optical flow problem in computer vision. VMamba represents a powerful approach to long-range spatial modeling via 2D-selective-scan (SS2D), offering a compelling alternative to traditional convolutional or transformer-based backbones that have previously been used for digital image correlation (DIC). Leveraging VMamba’s efficient image-patch token interaction mechanism, we develop a methodology that pretrains and finetunes the end-to-end model tailored for speckle image optical flow, aiming to capture both high-frequency deformation features and smooth global displacements with improved fidelity. A comprehensive evaluation on synthetic and real-world datasets demonstrates that our VMamba-based model consistently surpasses existing CNN- and transformer-based DIC methods in accuracy and robustness across a wide range of spatial frequencies. These results underscore VMamba’s promise as a powerful foundation for next-generation DIC algorithms, advancing the computation of complex deformation fields in dynamic imaging.

Unphysical wave reflections pollute a domain’s solution when high frequency waves propagate from a fine to a coarse spatial discretisation. Inspired by the selective perfect matching layer, we look to specifically target and dampen the incompatible frequencies that cause the energy entrapment of spurious waves. In this work, we propose a Shepard-based projection method that filters with the inverse-distance weighting kernel—an alternative and simple to implement basis. We demonstrate the method in dynamically coupled finite element subdomains, that vary not only in mesh size, but also respective time steps. The attenuation is applied to a two-subdomain coupling, where explicit computations are leveraged to obtain a coarse-field representation of an interface. Performance of the proposed filter demonstrates a 99

This work presents the design and testing of an electric gun load intended for characterising the properties of materials under extreme conditions. Projectile launch techniques, such as gas guns and electromagnetic (EM) flyer plates, are capable of creating planar, high-pressure shocks across substantial material volumes, resulting in precise equation of state measurements. However, achieving these conditions necessitates specific flyer characteristics: the flyer must maintain near-constant density and velocity across a minimum thickness, in the direction of travel, until reaching the target. This has been achieved in EM flyer plates through sophisticated current pulse shaping (Lemke et al., 2014). This work involved the adaptation of an existing electric gun design to meet these criteria while utilising a relatively simple, fixed rise-time, pulsed-power driver instead. The proposed load achieves this by accelerating a 0.5-mm-thick insulating flyer whilst minimising state change (thus maintaining near-constant density) and eliminating the forces driving the flyer prior to impact by launching it across a stand-off distance (ensuring constant velocity). A combination of our 0D model (Fitzgerald et al., 2023) and a 2D in-house hydrocode were used to determine the optimal thicknesses for its constituent parts: the driving metal foil and plastic flyer. Experimental testing was conducted using a 140 kV electric gun load to validate the model's predictions and examine the correlation between the shock pulse shape at impact and the stand-off distance from the launch site. The results reveal the optimised load successfully generated a shock pulse in a PMMA target block with a magnitude of 20 GPa fora duration of 1.0 mu s, over region with 10 mm width, and at a 10 cm stand-off from the launch site. This large stand-off distance ensured the flyer was ballistic (constant velocity) on impact and also shielded the diagnostic line of sight from plasma generated on launch, allowing for precise measurements to be made. These outcomes suggest the electric gun technique can now be used to explore dynamic properties of materials using relatively simple pulsed-power devices with a fixed current rise-time.

This study presents the framework and implementation of a material strength model within a two-step Eulerian solution scheme in the MHD hydrocode, B2. The techniques presented in this work provide practical solutions to problems encountered when modelling high strain-rate behaviour of solids in an Eulerian framework. Several novel methods developed in this work resulted in the accurate reproduction of a Taylor anvil-on-rod test in B2 without a complex and computationally expensive interface reconstruction technique. These methods include a complete algorithmic definition of the different components of the stress tensor, ensuring realistic behaviour in low-density mixed cells at the rod-vacuum boundary through a density dependent modification of the yield, implementing automatically generated slip conditions at part boundaries, and damping oscillating numerical instabilities induced by the inclusion of strength. The Taylor test served as a rigorous verification case for the strength model, demonstrating the efficacy of these novel methods. A cross-code comparison against the results of a Lagrangian simulation in Ansys AUTODYN, a well-benchmarked commercial code which employs Young’s Reconstruction, of the Taylor rod deformation revealed a close match with the rod profile predicted by B2. In this article, emphasis is placed on the practical details of the routines required to implement these corrections to facilitate the adoption of three-dimensional material strength models in other Eulerian hydrocodes.

A Photon Doppler Velocimetry system that measures the propagation of elastic shear waves in a Torsion Hopkinson Bar (THB) system is presented. The method uses multiple fibre optic probes located symmetrically on opposing sides of the apparatus bars, and provides data with high spatial (a laser irradiated spot size of 35 mu m) and temporal resolution that is ultimately limited by the data acquisition system and used electronic components. A series of validation experiments simulating the movement of the bar subjected to bending and misalignments demonstrated that this approach is effective in detecting and accounting for the bending waves. The THB experiment under non-ideal conditions, where a combination of shear and bending waves propagates in the system, conclusively confirmed that the disturbance in the acquired signals can be properly addressed with the proposed arrangement of the PDV probes. It was reflected in similar measurements of the component of tangential velocity to the strain gauges. This approach shown to be complementary to the conventional strain gauge technique, but can provide better precision and be more robust under loading and/or temperature conditions that may affect the reliability of strain gauge measurements.

We report on recent developments that enable megahertz hard X-ray phase contrast imaging (MHz XPCI) experiments at the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument of the European XFEL facility (EuXFEL). We describe the technical implementation of the key components, including an MHz fast camera and a modular indirect X-ray microscope system based on fast scintillators coupled through a high-resolution optical microscope, which enable full-field X-ray microscopy with phase contrast of fast and irreversible phenomena. The image quality for MHz XPCI data showed significant improvement compared with a pilot demonstration of the technique using parallel beam illumination, which also allows access to up to 24 keV photon energies at the SPB/SFX instrument of the EuXFEL. With these developments, MHz XPCI was implemented as a new method offered for a broad user community (academic and industrial) and is accessible via standard user proposals. Furthermore, intra-train pulse diagnostics with a high few-micrometre spatial resolution and recording up to 128 images of consecutive pulses in a train at up to 1.1 MHz repetition rate is available upstream of the instrument. Together with the diagnostic camera upstream of the instrument and the MHz XPCI setup at the SPB/SFX instrument, simultaneous two-plane measurements for future beam studies and feedback for machine parameter tuning are now possible.

There are numerous examples in both the natural and applied worlds where shock compression and related phenomena play an important role. The montage shown in Fig. 1 highlights some of these, which span many orders of magnitude in pressure and length scale. At the lowest length scale, for example, shock compression is used to generate lattice-level defects as a means to increase the fatigue life of metal components. The technique, known as laser shock peening, modifies the near-surface region of a material, where the behavior of dislocations can be profoundly different than that at low strain rates. Shock also features prominently in the design of materials for protective applications. Intersection with advanced manufacturing in particular enables the tailoring of shock energy absorption to ultimately mitigate damage to structures and biological systems. Moving too much higher pressures, shock finds use as a tool to generate and study extreme states of matter relevant to energetic systems and inertial fusion schemes. Outstanding questions still remain regarding the effect of strength under such intense loading, especially in the case of mixed or partial melt conditions. And lastly, at the planetary scale, the shock has played an instrumental role in shaping the make up of the early solar system and accessing conditions within planetary bodies. Besides being used to study the makeup of asteroids (e.g., Deep Impact spacecraft in 2005), choreographed impacts have also been explored as a mechanism for asteroid redirection, as shown recently through the collision between the DART spacecraft and the Dimorphos asteroid in 2022.

This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress.

The electric gun is a projectile launcher which utilises both the rapid expansion of an ohmically heated exploding foil and strong electromagnetic forces to accelerate an insulating flyer up to 20 km/s. The gun’s acceleration mechanism is highly efficient at converting stored electrical energy in the pulsed-power device driving the load to kinetic energy in the flyer, with values of up to 25% reported (Osher et al., 1990). This high efficiency would allow capacitor banks to use less energy than conventional drives to generate higher pressure states in materials of interest to extreme state research. Despite its promising efficiency, the electric gun is rarely used, as the process of launching flyers above 0.5 mm thickness in this manner is highly variable, often resulting in uncontrolled launch characteristics and premature failure of the flyer. The gun is also difficult to optimise without use of a sophisticated multi-physics hydrocode, further limiting its take-up. This work presents experimental results from the successful launch of 24 × 24 mm flyers up to 2.0 mm thick to 10 km/s using an electric gun load on 1.2 MJ pulsed-power device: Machine 3. In combination with results from a 0D model, these findings are used to identify the mechanism for the destruction of thick flyers accelerated using electric guns, including strategies for mitigating their break-up. The results support the existing idea that flyer failure can be avoided by limiting the maximum pressure within the flyer. They also reveal a second mechanism by which the flyer integrity can be maintained when the current rise time is longer than the flight time; high pressures in thick flyers caused their density to remain high enough to prevent the driving foil plasma from breaking through, averting their disassembly. This second mechanism provides a route to accelerate thick electric gun flyers to higher velocities with efficiencies up to around 9% whilst lengthening the shock duration on impact, broadening the gun’s potential applications in extreme state research.

To investigate pressure states as extreme as those involved in inertial confinement fusion using projectile-driven impact, the projectile must be both moving at hypervelocity and thick enough to introduce a shock pulse sufficiently long as to be measured. The electric gun is a highly efficient pulsed-power projectile launcher: its unique drive mechanism has been reported to convert over 25% of a capacitor bank’s stored electrical energy to flyer kinetic energy (Osher et al., 1990). This high efficiency allows the gun to accelerate thin dielectric flyers to hypervelocity using relatively low energy machines (Weingart et al., 1979). However, the technique was unable to accelerate thick flyers (>0.5 mm) without causing the flyers significant damage, rendering it unsuitable for investigating extreme states of matter. In this work, previously existing results from the launch of a thin flyer on a low energy machine were analysed using a 0D electric gun model (Fitzgerald et al., 2023). The pressure states experienced by the flyer during this shot, performed in a well understood region of the electric gun parameter space, were used to inform the design of a new electric gun load, capable of launching thick flyers to hypervelocity. The experimental results of the testing of this load design on a 140 kV, 2.0µs rise-time machine are presented. The load was found to successfully accelerate intact flyers up to 2.0-mm-thick, introducing shock speeds of over 10 km/s in a PMMA target block, inducing pressures of 80 GPa. This is twice as thick as those reported previously (Song et al., 2018). The outcomes of the study suggest the results from previous low-risk shots can be used to develop electric gun loads in new regions of the design space using simplified modelling tools.

The intersection of dynamic compression, high-rate material response and X-ray science has seen rapid growth, leading to the establishment of specialized end-stations at international facilities such as Linac Coherent Light Source LCLS (Matter at Extreme Conditions - MEC) and Advanced Photon Source APS (Dynamic Compression Sector - DCS), both USA. Although these facilities excel in working with X-rays tailored for small material volumes (i.e. <1mm(3)), it needs a different approach to delve into subsequent processes. This is particularly the case in the transition from the micro- to mesoscale: here the ESRF distinguishes itself. The large beam size (several cm(2)) of the ID19 beamline, in conjunction with a strong high energy component, source flux density, and outstanding imaging sensitivity, enables sub-surface visualization of engineering-scale structures as well as natural systems in representative volume, under high rate and shock. This is particularly valuable when studying materials with complex mesostructures and heterogeneities on relevant volumetric scales, which often dominate the dynamic material response. The study of the behavior of materials under dynamic loading presents a unique challenge due to inherently spanning over multiple lengths- and timescales. The evolution of sudden (thermo)mechanical excitation, starting from the lattice scale and progressing through grains, phase domains, and ultimately to structures, exhibits a spectrum of responses spanning from the microscopic to bulk length scales. Consequently, a diverse range of diagnostics as well as driver instrumentation is required to identify, study, and characterize this material response spectrum. This article shall introduce platforms available at beamline ID19 and underline their potential by selected showcase applications. Community access proposals such as the beamtime Block Allocation Group (BAG) allow for access in a routine manner.

Each year approximately 99% by mass of energetic material use takes place in the quarrying, mining, construction and petrochemical industries. The coupling of explosively driven shock waves to heterogeneous geological materials is of scientific and industrial relevance. Here we report the first experiments conducted with energetic materials at the ID19 beamline at the European Synchrotron Research Facility, Grenoble, France. The experiments used commercial detonators to explosively load sand samples and glass spheres. Time resolved images showing the compaction wave produced by the explosive loading of both coarse- and fine-grained sand as well as large and small diameter glass spheres.

This paper presents an approach to evaluate the failure of arbitrarily inclined interfaces using FE models with structured spatial discretization, providing accurate prediction of crack propagation along paths known a priori that are not constrained to the element boundaries. The combination of algorithms for the generation of structured discretization of representative polycrystalline microstructures with novel cohesive element formulations allow modelling the failure of complex topologies along rasterised boundaries, with noticeably higher computational efficiency and comparable accuracy. Two formulations of raster cohesive elements are presented, adopting either elastic-brittle or Tvergaard–Hutchinson traction separation laws. The formulations proposed are first validated comparing the failure of the interface within bi-crystal structures discretised using hexahedral elements either within a structured mesh (i.e. with rasterised boundaries) or an unstructured mesh (i.e. with planar boundary). Subsequently, the effectiveness of the formulations is demonstrated comparing the inter-granular crack propagation within complex polycrystalline microstructures. The behaviour of the novel cohesive element formulation in structured meshes consisting of regular hexahedral elements is in excellent agreement with the deformation and failure of classic cohesive element formulations placed along the planar boundaries of unstructured meshes consisting of tetrahedral elements. The higher computational cost of the raster cohesive elements is more than compensated by the increase in computational efficiency of structured meshes when compared to unstructured meshes, leading to a reduction of the simulation time of up to over 200 times for the simulations presented in the paper, thus allowing the simulation of large domains.

The effects of cold work on dynamic flow strength is studied through measurements of dislocation density and elastic precursor attenuation in shocked aluminium. High-purity aluminium and Al 6082 alloy samples are subjected to up to three passes of rotary swaging, a severe plastic deformation (SPD) technique, in order to produce large variations in starting material conditions. Detailed material characterisation is performed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) to determine the initial dislocation density, texture, grain boundary density and misorientation distribution. Variations in dynamic strength are studied through the evolution of the elastic precursor amplitude with propagation distance in specimens with thicknesses between 0.2 and 1 mm, shock loaded to impact stresses of about 4.6 GPa. It is shown that dynamic strength decreases with increasing initial dislocation density in both materials, demonstrating rare, quantified measurements of a reversal in the effect of dislocation density on yield strength at strain rates around 10 ^4 s ^-1 and above.

The present study demonstrates experimental evidence of subsurface mesoscale damage initiation and evolution in angle-ply CFRP laminates under high strain-rate loading at low temperatures using synchrotron-based X-ray MHz radiography. A bespoke set of loading, temperature control and in-situ X-ray imaging systems were applied to simultaneously correlate high strain-rate mechanical response with observed subsurface damage in a time-resolved manner. The results demonstrate that independent of temperature, damage evolved following a specific sequence; firstly intra-ply shear cracking along the fibre direction, developing into multi-layer cracking with continued deformation, and finally culminating in inter-ply delamination and complete failure of the specimen. The timescale for this sequence, however, was observed to strongly depend upon temperature, with low temperatures resulting in more rapid damage evolution and loss of mechanical strength.