Explore the vast range of titles available.

Cuttlefish, a unique group of marine mollusks, produces an internal biomineralized shell, known as cuttlebone, which is an ultra-lightweight cellular structure (porosity, ∼93 vol%) used as the animal’s hard buoyancy tank. Although cuttlebone is primarily composed of a brittle mineral, aragonite, the structure is highly damage tolerant and can withstand water pressure of about 20 atmospheres (atm) for the species Sepia officinalis. Currently, our knowledge on the structural origins for cuttlebone’s remarkable mechanical performance is limited. Combining quantitative three-dimensional (3D) structural characterization, four-dimensional (4D) mechanical analysis, digital image correlation, and parametric simulations, here we reveal that the characteristic chambered “wall–septa” microstructure of cuttlebone, drastically distinct from other natural or engineering cellular solids, allows for simultaneous high specific stiffness (8.4 MN·m/kg) and energy absorption (4.4 kJ/kg) upon loading. We demonstrate that the vertical walls in the chambered cuttlebone microstructure have evolved an optimal waviness gradient, which leads to compression-dominant deformation and asymmetric wall fracture, accomplishing both high stiffness and high energy absorption. Moreover, the distribution of walls is found to reduce stress concentrationswithin the horizontal septa, facilitating a larger chamber crushing stress and a more significant densification. The design strategies revealed here can provide important lessons for the development of low-density, stiff, and damage-tolerant cellular ceramics.

Complex and vertically overlapped lithologies exist for the high-quality shale oil reservoir of the Lianggaoshan formation in the Sichuan basin. Continental shale oil reservoirs grow bedding, lamina, and natural fractures, challenging fracture network morphology control and monitoring in horizontal well multistage fracturing technology. This study proposed a true triaxial monitoring method based on distributed fiber optic sensing for the outcrops with good emergence, occurrence, and clear lithology. The U-shaped plane layout style is adopted to monitor the initiation and propagation of hydraulic fracturing in the full-time domain. The study first found that the main vertical fracture perpendicular to the wellbore and lamina fracture had an asymmetric propagation pattern, and fracture initiation was instantaneous and had a characteristic of elastic recovery. The asymmetric propagation of multistage/multicluster fractures can be grouped into nine types combing with the relative angle and position variation. Simultaneously, there is a 2-s time difference when the vertical fracture reaches the boundary on two sides and an included angle between the vertical fracture and the maximum horizontal principal stress. Besides, the low-viscosity slick water will filtrate into the existing lamina plane after the initiation of vertical fracture under high-pressure pumping. It is helpful to open the lamina and form a complex fracture network of vertical fracture cross lamina fracture, usually in the form of a cross, I-shaped, and fishbone. This experimental study can effectively improve the calculation accuracy of stimulated reservoir volume (SRV) and shale oil production and guide the fracturing stimulation monitoring of adjacent wells.HighlightsThis study proposed a physical monitoring method for laboratory true triaxial fracturing based on distributed fiber optic sensing.The asymmetric propagation pattern of fracture swarms in laminated continental shale oil reservoirs reflected the propagation speed and orientation.This article found a strain elastic recovery property after the vertical hydraulic initiation, which can guide the sand addition timing.This research summarized nine asymmetric propagation behaviors and three fracture network morphologies in the oilfield.

Stress interference is the main factor affecting hydraulic fracture propagation during multi-well hydraulic fracturing; stress interference is influenced by fracture bending, fracture hits, and asymmetric fracture propagation. To investigate the role of stress interferences among hydraulic fractures with nonuniform stress distribution in an inhomogeneous formation, a hydromechanical coupling extended finite element method was adopted to investigate the fracturing paths that occurred during the first fracturing–fracturing fluid flowback–repeat fracturing process; the asymmetric fracturing that occurred at different child well locations was also studied. The results showed that the area affected by fracturing-induced stress formed a “butterfly type” area. For child wells located within the zone, stress interference resulted in asymmetric fracture propagation; meanwhile, for child wells located outside this zone, stress interference resulted in symmetric fracture geometry. The effect of stress interference on the asymmetry of child well fracture wings was found to be negatively correlated with the distance between the parent well and the child well.

One of the typical anisotropic media is the monoclinic anisotropy (MA) medium, which is formed by embedding two sets of non-orthogonal fracture sets into an isotropic or vertical transverse isotropic (VTI) background medium. Weak anisotropy (WA) parameters and fracture density provide important in situ stress and high-porosity zone information. Estimation of WA parameters and fracture density of MA medium by prestack seismic amplitude inversion is important for shale reservoir characterisation. We derive the expression of generalised WA parameters in a basic reflection coefficients formula of MA medium by incorporating a stiffness matrix of VTI background and disturbance compliance matrix of asymmetric fracture. We then re-express the P-wave reflection coefficients in terms of WA parameters and fracture compliance tensors. To achieve the direct inversion of fracture density, we rewrite the linearised expression of P-wave reflection coefficients related to WA parameters and fracture density. Finally, under the Bayesian framework, the WA parameters and fracture density are estimated by using the amplitude versus offset and azimuth (AVOA) inversion parameters. We use a Monte Carlo simulation to test the effect of uncertainties in the priori information about fracture property parameters. The application of synthetic seismic gathers show that the proposed inversion strategy is reliable within moderate noise. Compared with the results obtained by using inversion based on a rotationally invariant fracture, the test indicates that a fracture model with a simplified shape or wrong assumption will increase calculation error and reduce the inversion accuracy.

We propose large-diameter (160 mm) pre-cracked chevron notched Brazilian disc (P-CCNBD) specimens were used to study the asymmetric fracture law and determine the dynamic fracture toughness of rock. Specimens were diametrically impacted by a split Hopkinson pressure bar. The dynamic fracture failure process of each specimen was monitored by crack propagation gauges and strain gauges. Each of the large-diameter P-CCNBD specimens was found to exhibit prominent asymmetric fracture under impact load. The stress equilibrium condition cannot be satisfied. The dynamic fracture toughness values of the rocks were measured using the experimental-numerical method rather than the quasi-static method. The calculation results showed that the dynamic fracture toughness of rocks increases with the dynamic loading rate. In addition, at the 3-D crack front, the dynamic stress intensity factor was found be substantially different at each point. These data suggest that the dynamic fracture toughness of P-CCNBD specimens should be calculated by removing the value affected by an edge arc crack and taking the average value of the remaining points. nema

Background Bipedicular/unipedicular percutaneous kyphoplasty are common treatments for OVCF, and there are no studies to show which is more beneficial for AVCF. The purpose of this study was to investigate the clinical efficacy of BPKP or UPKP in the treatment of AVCF. Methods The clinical data of AVCF patients treated by PKP were retrospectively analyzed. They were divided into two groups according to the surgical approach. General demographic data, perioperative complications, and general information related to surgery were recorded for both groups. The preoperative and postoperative vertebral height difference, vertebral local Cobb angle, lumbar pain VAS score and lumbar JOA score were counted for both groups. The above data were compared preoperatively, postoperatively and between the two groups. Results 25 patients with AVCF were successfully included and all were followed up for at least 12 months, with no complications during the follow-up period. 10 patients in the BPKP group and 15 patients in the UPKP group, with no statistically significant differences in general information between the two groups. The VAS scores of patients in the BPKP group were lower than those in the UPKP group at 12 months after surgery, and the differences were statistically significant, and there were no statistically significant differences between the two groups at other follow-up time points. In the BPKP group, 80% of patients had symmetrical and more homogeneous bone cement dispersion. 50% of patients in the UPKP group had a lateral distribution of bone cement and uneven bone cement distribution, and the difference in bone cement distribution between the two groups was statistically significant. Conclusion For the treatment of AVCF, the clinical efficacy of both surgical approaches is basically the same. The distribution of cement is more symmetrical and uniformly diffused in the BPKP group, and the clinical efficacy VAS score is lower in the long-term follow-up. Bipedicular percutaneous kyphoplasty is recommended for the treatment of AVCF. The ethical review batch number XZXY-LJ-20161208-047.

In the study, a combined numerical simulation and on‐site monitoring method was used to analyze the asymmetric development characteristics of overlying rock fractures in a goaf under the condition of a goaf side entry formed by roof cutting and to explore the gas accumulation area in the goaf, achieving precise gas extraction from the goaf. The results demonstrates that a double‐balanced arch structure is formed under the condition of a goaf side entry formed by roof cutting, achieving safe retention of the roadway and showing the significance of the pressure relief effect of roof cutting. The collapse movement of the overlying rock on the roof‐cutting side is relatively advanced. The heights of the collapse zone on the roof‐cutting side and the uncut roof side are 28 and 24 m, respectively, and the development heights of the fracture zone are 37 and 42 m, respectively. The fault line on the roof‐cutting side gradually shifts toward the direction of the goaf, and the surface settlement and fracture development are relatively small. There is a clear asymmetric structure in terms of time effect, fault line, fracture zone height, and surface settlement compared to the uncut roof side. The gas is distributed throughout the entire goaf in the roof‐cutting and tunneling mode, and a high‐concentration gas accumulation area is formed near the open–off cut and working face on the high side of the fracture zone. Based on an actual situation, a method of drilling high and low positions in a fracture zone is proposed for extraction. Combined with on‐site monitoring, the goaf was no longer filled with gas during extraction, and the proportion of low‐concentration gas space considerably increased. A combined numerical simulation and on‐site monitoring method was used to analyze the asymmetric development characteristics of overlying rock fractures in a goaf under the condition of a goaf side entry formed by roof cutting and to explore the gas accumulation area in the goaf, achieving precise gas extraction from the goaf. The results demonstrate a double‐balanced arch structure is formed under the condition of a goaf side entry formed by roof cutting, achieving safe retention of the roadway and showing the significance of the pressure relief effect of roof cutting.

An elastic analysis of an internal crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane is studied, and asymmetrical dynamic fracture model of bridging fiber pull-out of unidirectional composite materials is presented for analyzing the distributions of stress and displacement with the internal asymmetrical crack under the loading conditions of an applied non-homogenous stress and the traction forces on crack faces yielded by the bridging fiber pull-out model. Thus the fiber failure is ascertained by maximum tensile stress, the fiber ruptures and hence the crack propagation should also appear in the modality of self-similarity. The formulation involves the development of a Riemann-Hilbert problem. Analytical solution of an asymmetrical propagation crack of unidirectional composite materials under the conditions of two increasing loads given is obtained, respectively. In terms of correlative material properties, the variable rule of dynamic stress intensity factor was depicted very well. After those analytical solutions were utilized by superposition theorem, the solutions of arbitrary complex problems could be gained.

Background Simultaneous bilateral hip fractures without major trauma in the elderly are rare and usually symmetrical. To the best of our knowledge, only two cases of bilateral simultaneous asymmetric hip fracture in the elderly without major trauma have been reported. Case presentation We present the case of a 90-year-old Japanese man with simultaneous bilateral asymmetric hip fractures with trochanteric fracture on the right side and greater trochanteric fracture on the left side. He complained of dyspnea at midnight and was referred to our emergency department. He was admitted to the internal medicine department for bacterial pneumonia treatment. On the 8th day of hospitalization, he was referred to our orthopedic surgery department for hip pain and was found to have fractures of both hips. Computed tomography findings showed that the left femoral neck fracture was an old fracture, while the left greater trochanteric fracture and the right trochanteric fracture were fresh fractures. He was surgically treated through open reduction and internal fixation with an intramedullary nail on the right and hemiarthroplasty on the left in supine position, performed during the same surgical sessions on the 12th day of hospitalization. Conclusions We report a new form of simultaneous bilateral asymmetric hip fracture in the elderly. The fracture types of the case were femoral trochanteric fracture and greater trochanteric fracture of the femur, which were different from the fracture types in the previously reported two cases. Clinicians should be aware of the possibility of simultaneous bilateral hip fractures, especially in the elderly.

In engineering practice, layered rock masses often display obvious anisotropy while deforming and failing, and the failure mode directly impacts the engineering construction stability. In this study, the fracture failure load, fracture toughness, crack deflection angle, and failure mode of a layered rock mass under different fracture modes were analyzed by utilizing improved asymmetric semi-circular disc specimens. According to the constitutive model of transversely isotropic materials, the maximum tensile stress (MTS), maximum energy release rate (MERR), and maximum strain energy density (MSED) calculation formulas were modified, and the calculation formulas of the three prediction criteria under anisotropic materials were derived. The calculation results were compared with the experimental results. The results show that the fracture toughness and crack deflection angle were significantly affected by the weak bedding plane. As a result of applying the MTS criterion, the results are closer to the experimental results, providing a solid foundation for engineering deformation, failure, and fracture analyses.