The seed coat of tobacco displays an intriguing cellular pattern characterised by puzzle-like shapes whose specific function is unknown. Here, we perform a detailed investigation of the structure of tobacco seeds by electron microscopy and then follow the germination process by time lapse optical microscopy. We use particle image velocimetry to reveal the local deformation fields and perform compression experiments to study the mechanical properties of the seeds as a function of their hydration. To understand the mechanical role of the observed coat structure, we perform finite element calculations comparing structure with puzzle-shaped cells with similar structures lacking re-entrant features. The results indicate that puzzle-shaped cells act as stress suppressors and reduce the Poisson’s ratio of the seed coat structure. We thus conclude that the peculiar cellular structure of these seed coats serves a mechanical purpose that could be relevant to control germination.

Previous studies on the relationship between dairy consumption and hip fracture risk have reported inconsistent findings. Therefore, we aimed to conduct an algorithmically driven non-linear dose-response meta-analysis of studies assessing dairy intake and risk of developing incident hip fracture. Meta-analysis from PubMed and Google Scholar searches for articles of prospective studies of dairy intake and risk of hip fracture, supplemented by additional detailed data provided by authors. Meta-regression derived dose-response relative risks, with comprehensive algorithm-driven dose assessment across the entire dairy consumption spectrum for non-linear associations. Review of studies published in English from 1946 through December 2021. A search yielded 13 studies, with 486 950 adults and 15 320 fractures. Non-linear dose models were found to be empirically superior to a linear explanation for the effects of milk. Milk consumption was associated with incrementally higher risk of hip fractures up to an intake of 400 g/d, with a 7 % higher risk of hip fracture per 200 g/d of milk (RR 1⋅07, 95 % CI 1⋅05, 1⋅10; P < 0⋅0001), peaking with 15 % higher risk (RR 1⋅15, 95 % CI 1⋅09, 1⋅21, P < 0⋅0001) at 400 g/d versus 0 g/d. Although there is a dose-risk attenuation above 400 g/d, milk consumption nevertheless continued to exhibit elevated risk of hip fracture, compared to zero intake, up to 750 g/d. Meanwhile, the analysis of five cohort studies of yoghurt intake per 250 g/d found a linear inverse association with fracture risk (RR 0⋅85, 95 % CI 0⋅82, 0⋅89), as did the five studies of cheese intake per 43 g/d (~1 serving/day) (RR 0⋅81, 95 % CI 0⋅72, 0⋅92); these studies did not control for socioeconomic status. However, no apparent association between total dairy intake and hip fracture (RR per 250 g/d of total dairy = 0⋅97, 95 % CI 0⋅93, 1⋅004; P = 0⋅079). There were both non-linear effects and overall elevated risk of hip fracture associated with greater milk intake, while lower risks of hip fracture were reported for higher yoghurt and cheese intakes.

Previous hydrocarbon explorations in the middle of the Tarim Basin indicate that strike-slip faults play an important role in the development of Ordovician carbonate reservoirs and hydrocarbon accumulation. The SB5 fault in the Tarim Basin was the target of this investigation. An evaluation of the stress in situ was carried out and provided boundary conditions to build a 3D geomechanical model. The distribution and application of present in situ stress in the strike-slip fault were studied. The results show good agreement between the absolute measured stress in situ and the modelled stresses, revealing a different stress regime along the strike-slip fault. The uplift segment belongs to a strike-slip stress state, and other areas belong to a normal fault stress state. The strike-slip fault has a significant influence on the present in situ stress distribution. The direction of the maximum horizontal stress deflects near the fault and tends to be parallel to the fault strike. This work introduces a comprehensive evaluation of the present in situ stress of the fractured carbonate reservoirs controlled by the strike-slip fault system. The present in situ stress direction can clarify the propagation direction of hydraulic fracturing and serve to evaluate the effectiveness of natural fractures.

Intermetallic γ-TiAl-based alloys are commonly used as structural materials for components in high-temperature applications, although they generally suffer from a lack of ductility and crack resistance at ambient temperatures. Within this study, the process-adapted 4th generation TNM+ alloy, exhibiting a fully lamellar microstructure, was examined using notched micro-cantilevers with defined orientations of lamellar interfaces. These configurations were tested in situ using superimposed continuous stiffness measurement methods during loading with simultaneous scanning electron microscopy observations. Subsequently, the video signal was used for visual crack length determination by computer vision and compared to values calculated from in situ changes in stiffness data. Applying this combinatorial approach enabled to determine the J-integral as a measure of the fracture toughness for microstructurally different local crack propagation paths. Thus, distinct differences in conditional fracture toughness could be determined from 3.7 MPa m1/2 for γ/γ-interface to 4.4 MPa m1/2 for α2/γ-interface.

The plasticity of body-centered cubic (bcc) metals is dependent of temperature as well as sample dimension at the micrometer scale, but the effects of cryogenic temperature on the plasticity and the related failure process in micron-sized bcc metals have not been studied under uniaxial tension. In this work, we utilized in situ cryogenic micro-tensile tests, transmission electron microscopy, and dislocation dynamic simulations to examine the plasticity and failure processes of [001]-oriented bcc niobium micropillars. Our study reveals that a strong suppression of cross-slip at low temperatures prevents dislocation multiplication and leads to a dislocation starvation state, at which no mobile dislocation exists due to the rapid annihilation of dislocations at free surfaces. New dislocations are then nucleated until stress concentration at a slip step creates a micro-crack, the propagation of which leads to catastrophic failure. This unique failure process results from the combined effects of sample dimension and temperature.

In this study, a spherical indenter mounted on an atomic force microscope (AFM) was used to compress a Nannochloropsis oculata (N. oculata) cell on a poly-l-lysine coated slide. A mathematical model of the cell, which was derived by considering a fluid-filled spherical shell with axisymmetric compression between a sphere and an infinite flat plate, is proposed. In the construction of this mathematical model, the spherical shell was assumed to be a homogenous, isotropic, and elastic material. Thin-film theory was applicable to the spherical shell because the thickness of the shell was nearly negligible compared with its diameter. The governing equations of the contact and noncontact regions were converted from a boundary condition problem to an initial value problem. Then, the fourth-order Runge–Kutta method was applied to solve the transformed governing equations. The force curve obtained from the compression experiment was compared with the theoretical results derived from the proposed model. Furthermore, the numerical solution of the proposed model was verified to be consistent with the experimental data. The mechanical properties of cell walls were confirmed by applying the least square error method. Subsequently, the contact radius, inner pressure and tension distribution of the cell wall could be determined using the proposed model. The models proposed in other studies are suitable for analyzing the compression characteristics of cells whose size is of the order of tens of micrometers and millimeters. By contrast, the model proposed in this study can analyze the compression characteristics of N. oculata, which is only a few micrometers in diameter. Furthermore, a force curve that accurately describes the deformation behavior of N. oculata under strain levels of 25% was established.

Hydrogels have gained recent attention for biomedical applications because of their large water content, which imparts biocompatibility. However, their mechanical properties can be limiting. There has been significant recent interest in the strength and fracture toughness of hydrogel materials in addition to their stiffness and time-dependent behavior. Hydrogels can fail in a brittle manner, although they are extremely compliant. In this work, the failure and fracture of hydrogels are examined using a compression test of spherical hydrogel particles. Spheres of commercially available polyacrylamide–potassium polyacrylate were hydrated and tested to failure in compression as a function of loading rate. The spheres exhibited little relaxation when compressed to small fixed displacements. The distributions of strength values obtained were examined in a particle fracture framework previously used for brittle ceramics. There was loading rate dependence apparent in the measured peak force and calculated peak strength values, but the data fell on a single empirical distribution function of strength for the hydrogels regardless of loading rate. Strength values for these hydrogels were mostly in the range of 0.05–0.3 MPa, illustrating the challenges using hydrogels for mechanically demanding applications such as tissue engineering.

The prediction of crack propagation is an important engineering problem. In this work, combined with triangular plane stress finite elements, a new remeshing algorithm for crack opening problems was developed. The proposed algorithm extends the crack iteratively until a threshold maximum crack length is achieved. The crack propagation direction is calculated using the maximum tangential stress criterion. In this calculation, in order to smoothen the stress field in the vicinity of the crack tip, a weighted average of the stresses of the integration points around the crack tip is considered. The algorithm also ensures that there are always at least eight elements and nine nodes surrounding the crack tip, unless the crack tip is close to a domain boundary, in which case there can be fewer elements and nodes around the crack tip.

Four benchmark tests were performed showing that this algorithm leads to accurate crack paths when compared to findings from previous research works, as long as the initial mesh is not too coarse. This algorithm also leads to regular meshes during the propagation process, with very few distorted elements, which is generally one of the main problems when calculating crack propagation with the finite element method.

In this study, a peridynamic material model for a polycrystalline ice is utilised to investigate its fracture behaviour under dynamic loading condition. First, the material model was validated by considering a single grain, double grains and polycrystalline structure under tension loading condition. Peridynamic results are compared against finite element analysis results without allowing failure. After validating the material model, dynamic analysis of a polycrystalline ice material with two pre-existing cracks under tension loading is performed by considering weak and strong grain boundaries with respect to grain interiors. Numerical results show that the effect of microstructure is significant for weak grain boundaries. On the other hand, for strong grain boundaries, the effect of microstructure is insignificant. The evaluated results have demonstrated that peridynamics can be a very good alternative numerical tool for fracture analysis of polycrystalline ice material.

When dealing with ice structure interaction modeling, such as designs for offshore structures/icebreakers or predicting ice cover’s bearing capacity for transportation, it is essential to determine the most important failure modes of ice. Structural properties, ice material properties, ice-structure interaction processes, and ice sheet geometries have significant effect on failure modes. In this paper two most frequently observed failure modes are studied; splitting failure mode for in-plane failure of finite ice sheet and out-of-plane failure of semi-infinite ice sheet. Peridynamic theory was used to determine the load necessary for inplane failure of a finite ice sheet. Moreover, the relationship between radial crack initiation load and measured out-of-plane failure load for a semi-infinite ice sheet is established. To achieve this, two peridynamic models are developed. First model is a 2 dimensional bond based peridynamic model of a plate with initial crack used for the in-plane case. Second model is based on a Mindlin plate resting on a Winkler elastic foundation formulation for out-of-plane case. Numerical results obtained using peridynamics are compared against experimental results and a good agreement between the two approaches is obtained confirming capability of peridynamics for predicting in-plane and out-of-plane failure of ice sheets.

Articular cartilage plays an important role in synovial joint function, but this function is diminished when cartilage tissue breaks down in osteoarthritis. Tissue engineering is a promising approach for replacing failed cartilage, as cartilage is a relatively simple tissue with no blood supply and very few biological cells. To imitate the structure of natural cartilage extracellular matrix material, three components must be included: the hydrated ground substance, the charges that contribute to compressive stiffness via electrostatic repulsion, and the nanofibrous collagen network that resists tensile deformation and failure. Here, the nanofiber network is considered, with examination of its fracture behavior in an as-electrospun state and following a mild chemical crosslinking process. Mode III fracture testing was used to quantify the tear toughness of the fibrous mats, and failure behavior was qualitatively examined with scanning electron microscopy. In ongoing work, this nanofibrous structure will be combined with a charged polyelectrolyte hydrogel gel to create a biomimetic cartilage-like material. By using biomimicry to replicate what is present in native cartilage tissue, a superior material can be designed and fabricated for use in tissue repair and replacement.

New forms of carbon-based materials have received great attention, and the developed materials have found many applications in nanotechnology. Interesting novel carbon structures include the carbon peapods, which are comprised of fullerenes encapsulated within carbon nanotubes. Peapod-like nanostructures have been successfully synthesized, and have been used in optical modulation devices, transistors, solar cells, and in other devices. However, the mechanical properties of these structures are not completely elucidated. In this work, we investigated, using fully atomistic molecular dynamics simulations, the deformation of carbon peapods under high-strain rate conditions, which are achieved by shooting the peapods at ultrasonic velocities against a rigid substrate. Our results show that carbon peapods experience large deformation at impact, and undergo multiple fracture pathways, depending primarily on the relative orientation between the peapod and the substrate, and the impact velocity. Observed outcomes include fullerene ejection, carbon nanotube fracture, fullerene, and nanotube coalescence, as well as the formation of amorphous carbon structures.