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In soft devices, complex actuation sequences and precise force control typically require hard electronic valves and microcontrollers. Existing designs for entirely soft pneumatic control systems are capable of either digital or analog operation, but not both, and are limited by speed of actuation, range of pressure, time required for fabrication, or loss of power through pull-down resistors. Using the nonlinear mechanics intrinsic to structures composed of soft materials—in this case, by leveraging membrane inversion and tube kinking—two modular soft components are developed: a piston actuator and a bistable pneumatic switch. These two components combine to create valves capable of analog pressure regulation, simplified digital logic, controlled oscillation, nonvolatile memory storage, linear actuation, and interfacing with human users in both digital and analog formats. Three demonstrations showcase the capabilities of systems constructed from these valves: 1) a wearable glove capable of analog control of a soft artificial robotic hand based on input from a human user’s fingers, 2) a human-controlled cushion matrix designed for use in medical care, and 3) an untethered robot which travels a distance dynamically programmed at the time of operation to retrieve an object. This work illustrates pathways for complementary digital and analog control of soft robots using a unified valve design.

Thin-ply composite failure modes also significantly differ from conventional ply composite failure modes, with the final failure mechanism switching from irregular progressive failure to direct fracture characterized by a uniform fracture with the reduction of the ply thickness. When open holes and bolt joints are involved, thin-ply-laminated composites exhibit more complex stress states, damage evolution, and failure modes. Compared to the experimental study of thin-ply-laminated composite-bolted joints, there are few reports about numerical analysis. In order to understand the damage evolution and failure mechanism of thin-ply-laminated composites jointed by single-lap bolt, a progressive damage model based on three-dimensional (3D) LaRC failure criterion combined with cohesive element is constructed. Through an energy-based damage evolution method, this model can capture some significant mechanical characteristics in thin-ply-laminated structures, such as the in situ effect, delamination inhibition, and fiber compressive kinking failure. The comparisons between the numerical predictions and experimental observations are made to verify the accuracy of the proposed model. It is found that the predicted stress-displacement curves, failure modes, damage morphologies, etc., are consistent with the experimental results, indicating that the presented progressive damage analysis method displays excellent accuracy. The predicted stress at the onset of delamination is 50% higher than that of the conventional thick materials, which is also consistent with experimental results. Moreover, the numerical model provides evidence that the microstructure of thin-ply-laminated composite performs better in uniformity, which is more conducive to inhibiting the intra-layer damage and the expansion of delamination damage between layers. This study on the damage inhibition mechanism of thin-ply provides a potential analytical tool for evaluating damage tolerance and bearing capabilities in thin-ply-laminated composite-bolted joints.

The LaRC02 criterion is a classical criterion for determining fiber kinking failure of UD laminates under longitudinal compression (LC), but its basis for determining matrix cracking in a fiber kinking coordinate system is based on stress-invariant theory rather than on a physical mechanism. Herein, three Puck-like physical-mechanism-based inter-fiber failure criteria are extended to LC failure of UD composites, and thus three failure criteria (denoted as LC-Guo, LC-Li, and LC-Puck failure criteria) are constructed for fiber kinking failure determination. The stresses in the global coordinate system are transformed to the fiber kinking coordinate system by a three-level coordinate system transformation, and then the failure determination is performed using the three Puck-like criteria. The results show that the overall accuracy of the three proposed criteria is higher than that of the LaRC02 criterion, especially the LC-Guo criterion. Additionally, an analysis of the influence of material properties shows that the failure envelope curves tend to be conservative, and the predicted off-axial compression strength decreases as the transverse compression strength and in-plane shear strength increase and the transverse tensile strength decreases. This work proposes a more reasonable assessment methodology for the determination of LC failure of UD composites, which has important theoretical significance and engineering value.

Fibre kinking is the most prevalent failure mode observed in UD composites. The accurate prediction of kinking failure is of paramount importance in industrial applications. To address this challenge, we develop a non-linear mean-field debonding model (NMFDM) based on our previous work, which efficiently captures the non-linear material behaviour of UD composites under longitudinal compression leading to kinking failure. Building upon the foundation of our earlier mean-field model, this enhanced NMFDM incorporates geometric non-linearity due to fibre rotation under longitudinal compression and the non-linear elasticity of fibres in the fibre direction. These additions address crucial aspects in kink band formation and the typically non-linear elastic behaviour of carbon fibres, which were not considered in our previous work. Additionally, we introduce a fibre kinking model (FKM) to predefine initial fibre misalignments in the geometries, allowing us to study the formation of kink bands. The FKM considers the effects of initial misalignments and fibre rotations during kinking by proposing a transformation law for off-axis cases. As a representative example, we investigate the initiation and evolution of kink band formation in an AS4/8552 UD composite by predefining various initial misalignments. The results demonstrate that our newly proposed NMFDM yields reliable predictions of kink band formation in UD composites, outperforming other existing models and even comparing favorably to micrograph observations of kink bands. Compared to our previous work, this enhanced model offers a more comprehensive understanding of kink band formation, particularly under large strains, by incorporating the non-linear elasticity of fibres in the fibre direction. This advancement opens up potential applications in designing composite structures with improved resistance to compressive failure, paving the way for broader applications in aerospace, automotive, and other industries where high-performance composite components are crucial.

An experimental investigation was focused on the failure behavior of unidirectional fiber-reinforced polymers when subjected to combined longitudinal/transverse compression and in-plane shear due to off-axis loading. Block-shaped and end-loaded specimens, spanning ten different fiber orientations (0°, 5°, 10°, 15°, 20°, 30°, 45°, 60°, 75°, and 90° with respect to the loading direction), were loaded to ultimate failure using a dedicated fixture. Different failure modes, including longitudinal compression, in-plane shear, and transverse compression, were identified, along with distinctive characteristics of the corresponding failure envelopes. Four physically based failure theories—Hashin, Camanho, Puck, and LaRC05—were subjected to a comparative analysis. Criteria derived from the concept of the action plane consistently outperformed in describing matrix-dominated failures, providing both qualitative and quantitative predictions of failure stresses and fracture plane orientation. However, for fiber-dominated failures, these theories seem to fall short in providing satisfactory predictions, particularly in accurately describing the influence of shear on fiber compression failure. Although criteria based on fiber-kinking theory can reasonably explain the formation of kink bands, they tend to yield overly conservative results. Recalibrations and minor refinement based on experimental results were implemented, leading to an improved agreement. Finally, the constructive role of off-axis compression tests in characterizing the failure behavior of unidirectional composites is discussed.

Extracranial internal carotid artery (EICA) kinking and coiling are the most frequently reported carotid anomalies in the literature. Embryogenic and acquired causes for such anomalies have been postulated but the prevalence of kinking and coiling has not been well characterized across age categories. The aim of this study is to evaluate the prevalence of EICA coiling and kinking among different age groups to better understand its potential causes and changes during the course of life. A total of 2856 subjects aged 0 to 96 years were studied by echo-color Doppler (ECD). Morphology and anatomical anomalies of the EICA were assessed. Patients with anatomical anomalies were stratified by age groups and the prevalence of EICA abnormalities was calculated. The maximal velocity recorded at the level of the kinking was compared with that measured in the common carotid artery and the peak systolic velocity kinking ratio (PSVKR) was calculated. A total of 284 subjects (9.94% of the sample) were found to have kinking or coiling of the EICA. The prevalence was significantly higher at the extremes of age (≤ 20 and > 60 years old, p < 0.001) supporting the hypothesis of a reduction with growth and a new increase in the elderly. PSVKR was higher in subjects with more severity kinking. This study showed a higher prevalence of EICA coiling and kinking in the very young and in the elderly. This bimodal prevalence distribution supports the hypothesis of a congenital anomaly that resolves with somatic growth, while advanced age with its many anatomical changes leads to its reappearance or worsening. Studies with longitudinal follow-up and paired observation are required to support this hypothesis.

Reproductive success depends on efficient sperm movement driven by axonemal dynein-mediated microtubule sliding. Models predict sliding at the base of the tail – the centriole – but such sliding has never been observed. Centrioles are ancient organelles with a conserved architecture; their rigidity is thought to restrict microtubule sliding. Here, we show that, in mammalian sperm, the atypical distal centriole (DC) and its surrounding atypical pericentriolar matrix form a dynamic basal complex (DBC) that facilitates a cascade of internal sliding deformations, coupling tail beating with asymmetric head kinking. During asymmetric tail beating, the DC’s right side and its surroundings slide ~300 nm rostrally relative to the left side. The deformation throughout the DBC is transmitted to the head-tail junction; thus, the head tilts to the left, generating a kinking motion. These findings suggest that the DBC evolved as a dynamic linker coupling sperm head and tail into a single self-coordinated system. Centrioles are ancient organelles with a conserved architecture and their rigidity is thought to restrict microtubule sliding. Here authors show that, in mammalian sperm, the atypical distal centriole and its surrounding atypical pericentriolar matrix form a dynamic basal complex that facilitates a cascade of internal sliding deformations, coupling tail beating with asymmetric head kinking.

NMR relaxation dispersion studies indicate that in canonical duplex DNA, Watson–Crick base pairs (bps) exist in dynamic equilibrium with short-lived low abundance excited state Hoogsteen bps. N1-methylated adenine (m1A) and guanine (m1G) are naturally occurring forms of damage that stabilize Hoogsteen bps in duplex DNA. NMR dynamic ensembles of DNA duplexes with m1A–T Hoogsteen bps reveal significant changes in sugar pucker and backbone angles in and around the Hoogsteen bp, as well as kinking of the duplex towards the major groove. Whether these structural changes also occur upon forming excited state Hoogsteen bps in unmodified duplexes remains to be established because prior relaxation dispersion probes provided limited information regarding the sugar-backbone conformation. Here, we demonstrate measurements of C3′ and C4′ spin relaxation in the rotating frame (R1ρ) in uniformly 13C/15N labeled DNA as sensitive probes of the sugar-backbone conformation in DNA excited states. The chemical shifts, combined with structure-based predictions using an automated fragmentation quantum mechanics/molecular mechanics method, show that the dynamic ensemble of DNA duplexes containing m1A–T Hoogsteen bps accurately model the excited state Hoogsteen conformation in two different sequence contexts. Formation of excited state A–T Hoogsteen bps is accompanied by changes in sugar-backbone conformation that allow the flipped syn adenine to form hydrogen-bonds with its partner thymine and this in turn results in overall kinking of the DNA toward the major groove. Results support the assignment of Hoogsteen bps as the excited state observed in canonical duplex DNA, provide an atomic view of DNA dynamics linked to formation of Hoogsteen bps, and lay the groundwork for a potentially general strategy for solving structures of nucleic acid excited states.

HighlightsFlexible films of kink porous carbon nanofibers are designed at the micro, meso and macro levelsThe fiber-film anodes with porous, kinked, and entangled network structures exhibit high rate and stability for potassium-ion storageWith the emergence of wearable electronics, flexible energy storage materials have been extensively studied in recent years. However, most studies focus on improving the electrochemical properties, ignoring the flexible mechanism and structure design for flexible electrode materials with high rate capacities and long-time stability. In this study, porous, kinked, and entangled network structures are designed for highly flexible fiber films. Based on theoretical analysis and finite element simulation, the bending degree of the porous structure (30% porosity) increased by 192% at the micro-level. An appropriate increase in kinking degree at the meso-level and contact points in entanglement network at the macro-level are beneficial for the flexibility of fiber films. Therefore, a porous and entangled network of sulfur-/nitrogen-co-doped kinked carbon nanofibers (S/N-KCNFs) is synthesized. The nanofiber films synthesized from melamine as nitrogen sources and segmented vulcanization exhibited a porous, kinked, and entangled network structure, and the stretching degree increased several times. The flexible S/N-KCNFs anode delivered a higher rate performance of 270 mAh g−1 at a current density of 2000 mA g−1 and a higher capacity retention rate of 93.3% after 2000 cycles. Moreover, the foldable pouch cell assembled by potassium-ion hybrid supercapacitor operated safely at large-angle bending and showed long-time stability of 88% capacity retention after 4000 cycles. This study provides a new idea and strategy for the flexible structure design of high-performance potassium-ion storage materials.

The direction of propagation of a straight-line plane crack in structurally inhomogeneous (grainy) materials under the combined effect of loading corresponding to fracture modes I and II is studied. The theoretical curve of the material strength or the Coulomb–Mohr curve type is assumed to be known. Based on the Neuber–Novozhilov force (integral) criterion relations are derived, which allow one to determine the angles of kinking (branching) of the crack path in the case of an arbitrary generalized stress state. Asymptotic presentations of the stress components in the vicinity of the crack tip take into account nonsingular terms ( -stresses). It is found that the crack can develop: 1) normal to the maximum stress direction if there are no shear stresses near the crack tip (Erdogan–Sih hypothesis) in the case of brittle fracture; 2) along the maximum shear direction if there are no normal stresses near the crack tip in the case of viscous fracture (in this case, a dislocation is emitted); 3) along a certain direction corresponding to a mixed stress state in the case of quasi-brittle or quasi-viscous fracture. The crack propagation direction depends on the ratio of the stress intensity factors for fracture modes I and II, sign of -stresses, and shape of the theoretical curve of strength on the plane of the critical states.