Recent investigations of fatigue failures in titanium alloys suggested a key role of low stress deformation events occurring at basal twist grain boundaries (BTGBs). The present study aims at clarifying the underlying mechanisms focusing on two representative BTGB configurations. Experimental characterization of the deformation behavior using high-resolution digital image correlation and molecular dynamics simulations highlighted differences in mechanical responses, although shear localization was exhibited along both BTGBs. The different strengths originate from kagome and triangular morphologies of the interfacial dislocation networks (IDN). Shear accommodation at low stress (i.e., similar to 100 MPa) was observed by collective glide of the triangular IDNs along [1100]. In contrast, shear localization at kagome IDNs was triggered by a transformation into triangular IDNs occurring at a higher stress level (i.e., similar to 1 GPa). The essential role of the stacking faults in the mechanical response is finally discussed.

This work explores the dynamic behavior of hybrid composite laminates reinforced with natural and carbon fibers, with a focus on their potential use in aeronautical structures requiring lightweight and high-performance materials, experimental and numerical investigations were performed on composite plates reinforced with natural fibers (glass/ natural fibers /epoxy and natural fibers/epoxy) and benchmarked against conventional magnesium alloys and carbon fiber reinforced plastics (CFRP), using advanced optical techniques and LMS vibration testing systems at the PPRIM Institute (Poitiers, France), the vibrational response of specimens with varying thicknesses was analyzed under free-free boundary conditions (for natural frequency and mode shape identification) and constrained conditions (to simulate operational constraints), the moir & eacute; method provided non-destructive and contactless measurements of out-of-plane displacements, results reveal that thin natural fiber reinforced plates (FRN) can achieve frequencies and mode shapes comparable to magnesium alloys and CFRP, while highlighting differences between material systems, these findings demonstrate that FRN-based hybrid composites offer promising vibration characteristics for aeronautical applications, combining structural efficiency with enhanced sustainability.

This study addresses one of the major factors affecting the metrological performance of Digital Volume Correlation (DVC), namely the systematic error caused by intensity interpolation, which is characterized by an S-shaped bias error. While random error can be reduced by improving image quality, systematic error cannot be avoided. To overcome this issue, a strategy called Shift-DVC is proposed to eliminate this systematic error in DVC.In classical DVC techniques, points of interest (POIs) are located at integer positions. In contrast, the proposed Shift-DVC strategy introduces specific offsets to the conventional positions, causing the POIs to be located at non-integer positions where the S-shaped bias error is reduced. This method, which is simple to implement in classical DVC code, reduces the intensity interpolation error by a factor of up to four and significantly decreases the computation time required for convergence.

Introduction: The existing body of literature on the biomechanical implications of ramp lesions is limited, leaving a significant gap in our understanding of how these lesions impact joint kinematics and loading in the medial compartment. This cadaveric biomechanical study aims to address this gap by employing an innovative Digital Volume Correlation (DVC) method, utilizing 7 Tesla Magnetic Resonance Imaging (MRI) images under various loading conditions. The primary objective is to conduct a comprehensive comparison of medial meniscal mobility between native knees and knees affected by grade 4 ramp lesions. By focusing on the intricate dynamics of meniscal mobility and extrusion, this work seeks to contribute valuable insights into the biomechanical consequences of medial meniscus ramp lesions.Materials and methods: An initial set of 7T MRI imaging sessions was conducted on two intact native knees, applying load values up to 1500N. Subsequently, a second series of images was captured on these identical knees, with the same loads applied, following the creation through arthroscopy of medial meniscus ramp lesions. The application of DVC enabled the precise determination of the three components of displacement and spatial variations in the medial menisci, both with and without ramp lesions.Results: The measured directional displacements between native knees and injured knees indicate that, following the application of axial compression load, menisci exhibit increased extrusion and posterior mobility as observed through DVC.Discussion: Injuries associated with Subtype 4 medial meniscus ramp lesions appear to elevate meniscal extrusion and posterior mobility during axial compression in the anterior cruciate ligament of intact knees. Following these preliminary results, we plan to expand our experimental approach to encompass individuals undergoing weight-bearing MRI. This expansion aims to identify meniscocapsular and/or meniscotibial insufficiency or rupture in patients, enabling us to proactively reduce the risk of osteoarthritic progression.

This work focuses on probability and statistical analysis, which presents the evaluation and scientific judgement of the results of our mechanical experiments and the calculation of fibre behaviour. The study was based on the energy method, the crushed section calculation method and the average (non-crushed) section calculation method. To achieve this objective, statistical methods are used to analyse the data of a process with two parameters, as advocated by Weibull, which gives good agreement for the elasticity coefficient and stress at failure for both the energetic and crushed section methods. To better understand at what level and where during the process, changes can be made to improve the technique of calculating mechanical behaviour, one-factor analysis of variance, Dunnett and Hsu’s multiple comparisons and Tukey and Fisher’s pairwise comparison were used to show the variance and differences between the three calculation methods. The experiment of the quasi-static tensile test was conducted on more than 500 artichoke fibre specimens and calculations using the three previous methods. This represents ten samples, which differ significantly in their mass and dimensions.

A nickel-based superalloy is examined during monotonic deformation from ambient to cryogenic temperatures, reaching as low as liquid helium temperature. A detailed multimodal analysis of the microstructure and plasticity is conducted to discern changes in deformation mechanisms and plastic deformation localization under cryogenic conditions. This study employs high-resolution digital image correlation and transmission electron microscopy to identify the deformation mechanisms and understand their influence on plastic deformation localization as the temperature varies. At cryogenic temperatures, unusual plastic deformation localization processes are observed, attributed to the competing activation of a range of deformation processes. Furthermore, a mechanism of slip delocalization, i.e., local plastic deformation homogenization through closely spaced slip, is noted at these extreme temperatures. Ultimately, the impact of the microstructure is identified across the temperature range, from room to cryogenic temperatures.

This work provides a comprehensive characterization and analysis of deformation and fatigue damage mechanisms in a nickel-based superalloy during ambient temperature fatigue and points to a fundamental deformation mechanism that results in the onset of crack nucleation. Strain and slip irreversibility are investigated at the nanometer scale using high-resolution digital image correlation and high-resolution electron backscatter diffraction, highlighting distinct deformation mechanisms contributing to crack nucleation. It is observed during early fatigue cycling at relatively low applied stress, the formation of intense slip events that induce grain boundary shearing. This results in intense micro-scale strain in the neighboring grains, producing localized plasticity and stresses. Such stresses facilitate fatigue extrusion–intrusion mechanisms during subsequent cycling, resulting in preferred crack nucleation. Finally, the configurations within the microstructure that promote such deformation and damage mechanisms sequence are highlighted.

Recent improvements in spatial resolution and measurement sensitivity for high-resolution digital image correlation (HR-DIC) now provide an avenue for the quantitative measurement of deformation events and capturing the physical nature of deformation mechanisms. However, HR-DIC measurements require significant time due to scanning electron image acquisition; such a limitation prevents the widespread use of HR-DIC for material characterization. Apply a novel SEM acquisition technology to enhance HR-DIC measurements for high throughput applications. Multi-beam SEM technology is employed to image an entire gauge length at once at high resolution and at nearly a hundredfold acceleration of typical HR-DIC image acquisition, even when automated stage movement and image acquisition are employed. These images were fed into a discontinuity-tolerant HR-DIC software to determine slip localization induced by non-metallic inclusions and grain structure. Slip localization was able to be analyzed to an unprecedented level, with over 210,000 slip bands able to be investigated, with the most intense slip localizing near and parallel to twin boundaries and in the vicinity of non-metallic inclusion clusters. Additionally, secondary slip activation and grain boundary shearing by intense dislocation pileups are observed to reduce slip amplitude near and parallel to twin boundaries. By performing HR-DIC in conjunction with a multi-beam SEM, high-throughput measurements of large field-of-view, high-resolution images were able to be performed in a timely manner. These measurements provided an immense number of slip events for statistical analysis to be performed on to relate to microstructural features.

The plastic instability evolution in polycrystalline metallic materials is a key to understanding the deformation processes during mechanical loading. Plasticity assessments of commercially pure titanium (CP-Ti) can be performed to enhance its mechanical properties. The aim of the present investigation is to determine the plastic deformation during the metal forming processes of CP-Ti sheets at room temperature. This localized deformation might affect the ductility of the sheets’ materials during the forming processes due to their complex strain paths. Therefore, this study is focused on the determination of Forming Limit Diagrams (FLDs) of CP-Ti sheets in different strain paths based on experimental Nakazima test. The latter is employed to determine the complete FLD using several specimens with various geometries to achieve different strain paths in tensile tests. For this purpose, the strain field measurements before cracking are carried out by the Digital Image Correlation (DIC) procedure. The detection of macroscopic cracks is determined by the Heaviside-DIC (H-DIC). During experimental tests, several images are taken with an integrated camera. The captured images are analyzed by DIC and H-DIC. In this work, a second depth camera is accurately calibrated. Thus, depth and standard cameras address most error sources inherent in the time-of-flight (ToF) technology within a unified calibration framework. Therefore, the automatic calibration method of the consumer ToF camera is used and developed for the first time with H-DIC technique, in the framework of material formability, to better determine the ductility limit of CP-Ti.

Hydroxyapatite (HA) ceramic scaffolds are commonly used as bone graft substitutes. Design of such scaffolds is a challenge to improve biological properties and extend the applications of HA ceramics in the field of bone tissue engineering. In this work, we investigated the processing and the in vitro properties of HA ceramic scaffolds mimicking human trabecular bone architecture. Samples of human tibial trabecular bone were collected (University Hospital Center of Limoges) and scanned by X-Ray μ-computed tomography (μ-CT) to generate 3D model database. From this computer-aided design, HA ceramic scaffolds were shaped layer-by-layer by additive manufacturing using laser stereolithography (SLA). Then, green parts were sintered to obtain dense ceramic scaffolds. The shaped parts were compared to the model (wall thickness, size, and geometry of the porous network) using image analysis. A good agreement was found. Only small differences were detected due to a light overpolymerization or to some unprinted very small details that were not linked to a polymerized area of the previous layer. Due to part shrinkage during sintering a magnifying factor has to be applied to the scanned CAO model to match the real dimensions of the trabecular bone sample. Human mesenchymal stem cell (hMSC) cultures were performed to investigate the biological properties of these scaffolds (cell attachment and proliferation of hMSC). These preliminary biological evaluations show the good biocompatibility and cell adhesion of the HA substitute. This work evidences the efficiency of SLA to produce ceramic scaffold architectures mimicking that of the natural trabecular bone with promising biological behavior.

The development of new percutaneous treatment techniques using a balloon for the reduction and cement for the stabilization for tibial plateau fractures (TPF) are promising. The biomechanical changes brought by the cement in the periarticular fracture are unknown. The objective of this study was to provide elements of understanding of the bone behavior in an epiphyseal fracture treated with cementoplasty and to define the modifications brought about by the presence of this cement in the bone from both an architectural and biomechanical point of view.In vitro animal experimentation was conducted. Bones samples were prepared with a cavity created with or without cancellous compaction, aided by balloon expansion following the same protocol as in the treatment of TPF. A uniaxial compression test was performed with various speeds and by using Heaviside Digital Image Correlation to measure mechanical fields. Preliminary finite element models were constructed with various boundary conditions to be compared to our experimental results.The analysis of the images permits us to obtain a representative load vs. time response, the displacement fields, and the strain distribution for crack initiation for each sample. Microcracks and discontinuity began very early at the interface bone/cement. Even when the global behavior was linear, microcracks already happened. There was no strain inside the cement. The finite element model that matched our experiments had no link between the two materials.In this work, the use of a novel correlation process highlighted the biomechanical role of the cement inside the bone. This demonstrated that there is no load transfer between bone and cement. After the surgery, the cement behaves like a rigid body inside the cancellous bone (same as a screw or plate). The cement provides good reduction and primary stabilization (mini-invasive approach and good stress distribution), permitting the patient to undergo rehabilitation with active and passive mobilization, but no weight-bearing should be authorized while the cortical bone is not consolidated or stabilized.

The vast diversity of morphologies, body size, and lifestyles of snakes represents an important source of information that can be used to derive bio-inspired robots through a biology-push and pull process. An understanding of the detailed kinematics of swimming snakes is a fundamental prerequisite to conceive and design bio-inspired aquatic snake robots. However, only limited information is available on the kinematics of swimming snake. Fast and accurate methods are needed to fill this knowledge gap. In the present paper, three existing methods were compared to test their capacity to characterize the kinematics of swimming snakes. (1) Marker tracking (Deftac), (2) Markerless pose estimation (DeepLabCut), and (3) Motion capture were considered. (4) We also designed and tested an automatic video processing method. All methods provided different albeit complementary data sets; they also involved different technical issues in terms of experimental conditions, snake manipulation, or processing resources. Marker tracking provided accurate data that can be used to calibrate other methods. Motion capture posed technical difficulties but can provide limited 3D data. Markerless pose estimation required deep learning (thus time) but was efficient to extract the data under various experimental conditions. Finally, automatic video processing was particularly efficient to extract a wide range of data useful for both biology and robotics but required a specific experimental setting.

Metallic materials experience irreversible deformation with increasing applied stress, manifested in localized slip events that result in fatigue failure upon repeated cycling. We discerned the physical origins of fatigue strength in a large set of face-centered cubic, hexagonal close-packed, and body-centered cubic metallic materials by considering cyclic deformation processes at nanometer resolution over large volumes of individual materials at the earliest stages of cycling. We identified quantitative relations between the yield strength and the ultimate tensile strength, fatigue strength, and physical characteristics of early slip localization events. The fatigue strength of metallic alloys that deform by slip could be predicted by the amplitude of slip localization during the first cycle of loading. Our observations provide a physical basis for well-known empirical fatigue laws and enable a rapid method of predicting fatigue strength as reflected by measurement of slip localization amplitude.

Using a combination of in-situ high-resolution digital image correlation (HR-DIC), Heaviside-DIC method (H-DIC), and crystal plasticity finite element (CPFE), we investigate the evolution of intragranular lattice rotations and slip activity during monotonic and cyclic loading in a high performance, polycrystalline face centered cubic material. The CPFE employs a quasi-3D model microstructure, which is a highly resolved mirror representation of the experimental in-situ test sample. In agreement, the measurements and calculations reveal that most grains, regardless of their size and lattice orientation, develop intragranular lattice rotation gradients that span the grain. For a small cluster of grains on the deformed material, we perform HR-DIC analysis of slip lines to demonstrate agreement in the active slip systems and changes in this local slip activity across the individual grains. The combined analysis reveals that deforming grains are divided into sub-granular regions of uniform lattice rotation and these regions are most often associated with only one or two active slip systems. The gradient lines that divide them correspond to changes in the predominant slip system. The model is used to examine the evolution of intragranular lattice rotation in a single fully reversed tension-compression cycle. The calculations indicate that intragranular gradients intensify during the reverse loading path as nearest neighboring regions appear to shed lattice rotation, increasing the lattice rotation in some regions, while shutting down rotation in neighboring regions. These findings provide insight into the irreversible changes that develop within deforming grains at the scale of the grain, particularly the heterogeneous development of intragranular lattice rotation in early stages of deformation, which could serve as precursors to localization.

Additively manufactured 316L stainless steels display significantly higher yield strength than their as-cast or wrought counterparts. This is associated with the micro-scale cellular structure and complex grain and sub-grain structure, resulting from high cooling rates occurring during the additive manufacturing process. The consequences of these peculiar microstructural features on plastic localization early in the plastic regime at the sub-grain scale are investigated. The plastic localization involved during monotonic deformation of conventional and additive manufactured 316L stainless steels is investigated using high-resolution digital image corre-lation. Significant heterogeneous slip localization is observed in the additively manufactured 316L stainless steels compared to the wrought 316L stainless steels. The cellular structure and low-angle grain boundaries are observed to control the incipient plasticity. In addition, slip localization characteristics indicate that the additional strengthening in the AM material is mainly related to the cellular structure acting as a dislocation forest-type obstacle.

The mechanical properties of polycrystalline metals are governed by the interaction of defects that are generated by deformation within the 3D microstructure. In materials that deform by slip, the plasticity is usually highly heterogeneous within the microstructure. Many experimental tools can be used to observe the results of slip events at the free surface of a sample; however, there are only a few methods for imaging these events in the bulk. In this article, the imaging of bulk slip events within the 3D microstructure are enabled by the combined use of X-ray diffraction contrast tomography and topotomography. Correlative measurements between high-resolution digital image correlation, X-ray diffraction contrast tomography, topotomography and phase contrast tomography are performed during deformation of Ti-7Al to investigate the sensitivity of the X-ray topotomography method for the observation of slip events in the bulk. Much larger neighborhoods of grains were able to be mapped than in previous studies, enabling quantitative measurements of slip transmission. Significant differences were observed between surface and bulk grains, indicating the need for 3D observations of plasticity to better understand deformation in polycrystalline materials.

The development of high-fidelity mechanical property prediction models for the design of polycrystalline materials relies on large volumes of microstructural feature data. Concurrently, at these same scales, the deformation fields that develop during mechanical loading can be highly heterogeneous. Spatially correlated measurements of 3D microstructure and the ensuing deformation fields at the micro-scale would provide highly valuable insight into the relationship between microstructure and macroscopic mechanical response. They would also provide direct validation for numerical simulations that can guide and speed up the design of new materials and microstructures. However, to date, such data have been rare. Here, a one-of-a-kind, multi-modal dataset is presented that combines recent state-of-the-art experimental developments in 3D tomography and high-resolution deformation field measurements.

This study reports on the mixed-mode behavior of desiccation cracks in a clayey rock front gallery. As most digital image correlation (DIC) algorithms have access to the full-field measurements of the displacements and strains, the improvements in DIC now allow the automatic detection of the jumps in the displacements induced by the opening and sliding of desiccation cracks without imposed initial conditions. This new local data allows us to specifically study the kinematics of the crack lips at each deformed state. These results allow us to quantify the opening and sliding of cracks and the cracked area during the desaturation and saturation paths of the rock mass. Amongst other results, a linear trend between the deformation of the solid phase and the crack porosity is observed. The results also demonstrate that most desiccation cracks evolve in a mixed-mode, the values of the shear component are of the same order of magnitude as the opening values.

Minimally invasive methods, such as balloon kyphoplasty (BKP) and percutaneous sacroplasty (PS), which are now widely used for the surgical treatment of compression fractures, involve injection of a bolus of poly (methyl methacrylate) bone cement (hereafter, "bone cement") into the fractured tissue. Many of the common complications following these surgeries, such as cement leakage and adjacent-level fractures (in the case of BKP), have been postulated to be related to the quality of the cancellous bone-bone cement interface, which, in turn, is a function of its fracture resistance. It is common to use bovine cancellous bone or polyurethane foam (PF) as a substitute for human cancellous bone in biomechanical studies of these surgical methods. The literature is lacking in studies of determination of fracture properties of human cancellous bone-bone cement interface, bovine cancellous bone-bone cement interface, and PF-bone cement interface. In the present work, an integrated methodology (combination of wedge splitting test and Heaviside-based digital image correlation) was used to make these determinations as well as those for the bone cement, bones and the PF alone. The fracture properties determined were maximum fracture load (F-max), fracture toughness (K-c), and specific fracture energy (G(f)). For example, G(f) values for human cancellous bone and human cancellous bone-bone interface were 0.48 +/- 0.14 N/mm and 0.38 +/- 0.05 N/mm, respectively, whereas in the case of bovine cancellous bone and bovine cancellous bone-bone cement interface, they were 1.08 +/- 0.11 N/mm and 0.22 +/- 0.05 N/mm, respectively, and for PF (Grades 12.5 and 15.0) and PF-bone cement interface, they were 0.81 +/- 0.12 and 0.55 +/- 0.06 N/mm, respectively. The same trends were seen in the F-max and K-c results. These results suggest that it may not be justified to use either bovine cancellous bone or either of the PF grades as a substitute for human cadaveric cancellous bone in biomechanical studies of BKP, PS, and similar surgical methods.

The slip localization behavior of the polycrystalline nickel base superalloy Inconel 718 during monotonic tensile loading at room temperature, is investigated for the first time in relation to the 3D microstructure. Multi-modal data merging tools are used to recombine high resolution digital image correlation (HR-DIC) data with 3D electron back-scatter diffraction tomography (3D EBSD), over a wide region of interest. This procedure enables reconstruction of the slip band planes in the 3D microstructure. Statistical analyses conducted over 500 individual slip bands reveal strong correlations between their location and specific microstructure configurations. In particular, over half of the slip bands emanate from triple junction lines (3D lines defined by the junction of three crystals). Moreover, the most intense and longest slip bands, which would become critical fatigue crack nucleation sites during cyclic loading, are located close and parallel to particular annealing twin boundaries and are simultaneously connected to triple junction lines. Crystal plasticity finite elements calculations are performed on the experimental microstructure to identify the slip activity that results in the formation of high intensity slip bands (localized plasticity) or zones of high lattice rotation (non-localized plasticity) in these particular microstructure regions.