Fracture Events Research Articles

Socio-demographic disparities in health-related quality of life after hip fracture in China: evidence from the China Health and Retirement Longitudinal Study.

Hip fractures cause high mortality and worsened health-related quality of life (HRQoL). This study aimed to investigate whether socio-demographic-related inequities in post-hip fracture participants' HRQoL exist in China. Data from the China Health and Retirement Longitudinal Study (waves 2013, 2015, and 2018) were used. The measurement of HRQoL in this study focused on 5 health dimensions: depression, body pain, mobility, basic activities of daily living, and instrumental activities of daily living. A difference-in-differences (DID) analysis with multiple time periods was performed to gauge the impact of hip fracture on HRQoL. A multivariate regression approach was used to explore socio-demographic-related factors associated with inequities of HRQoL. A total of 23,622 individuals were included, and 341 participants reported hip fracture events during the survey period. In participants with hip fracture, the presentation rate of body pain increased by 14% (p < 0.01) and the HRQoL of other health dimensions worsened (p ≤ 0.01) after hip fracture. The DID analysis showed that hip fracture had a negative impact on all HRQoL dimensions (p < 0.01). Socioeconomic-related factors of HRQoL inequities included school education level and location of residence. Study participants with hip fracture with greater educational attainment or living in urban areas had higher (p < 0.05) levels of HRQoL. In addition, comorbidities also correlated with a worse HRQoL (p < 0.05). Hip fracture significantly affects people's HRQoL in China, and the impact is more profound for those with lower educational attainment or living in rural areas. Targeted interventions should be designed to narrow this inequity.

Experimental and 2-Step Finite Element Analysis of Cyclic Fatigue Resistance of Conventional and Heat-Treated Rotary Endodontic Nickel-Titanium Instruments

Background: To evaluate the cyclic fatigue resistance of rotary endodontic nickel-titanium instruments using both experimental and finite element methods. Methodology: Four different proprietary rotary endodontic instruments (PTG, PTU, VB, and TRN) were subjected to cyclic fatigue tests through a custom-built fixture (n = 30 for each group) and tested until failure according to the manufacturer’s recommended settings, and the number of cycles to failure (NCF) was measured. Separated fragments were measured to determine the location of the fracture event. Finite element modeling replicated this experiment in silico via a two-step method, modeling the dynamic motion via an initial insertion step, then followed by rotation. Results: TRN showed the highest NCF (2027.94 ± 452.50) with the lowest values for strain (4.49% ± 0.23%) and fragment lengths (3.26 mm ± 0.47 mm), whereas PTU showed the lowest NCF (600.90 ± 80.86) and highest values for strain (6.29% ± 0.47%) and fragment lengths (5.36 mm ± 0.79 mm). All instruments showed an increase in von Mises and maximum principal stress during the insertion step but showed no changes to the maximum stress values during the rotational step. Conclusions: The finite element analysis approach used provided useful insights into the stress evolution and stress distribution of instruments during cyclic fatigue but lacked the ability with existing inputs to predict failure from cyclic fatigue.

Dynamic Fracture Resistance under Plane Strain Conditions of High-Density Polyethylene Nanoclay Composites.

Polymer nanoclay composites have received significant attention due to their substantially enhanced mechanical, thermal and barrier properties. However, the effect of these nanoclays on the dynamic fracture resistance of a polymer matrix during fast fracture events has not been documented. In this study, the effect of nanoclay addition on the rapid crack propagation (RCP) resistance of high-density polyethylene (HDPE) was investigated through the high-speed double torsion test. Results showed that the addition of 1, 3, and 5% of nanoclays improved the dynamic fracture resistance under the plane strain conditions (Gd1) of HDPE up to 65%. An increase in the storage and loss modulus, and a decrease in crystallinity and melt flow index with nanoclay content was also found. Although the presence of agglomerates can hinder the enhancement of Gd1 as it promotes agglomerate fracture and debonding, the increase in energy consumption through fibrillation and crazing promoted by the nanoclay prevails, suggesting that the nanoclay's toughening effect that has been extensively reported under quasi-static and impact tests, is also present under RCP conditions, and that the HDPE nanocomposites could be used in applications in which RCP must be prevented.

Higher Mortality Rate in Patients with Vertebral Compression Fractures is due to Deteriorated Medical Status Prior to the Fracture Event.

Vertebral compression fractures (VCF) are the most common low-energy fractures in older people and are associated with increased mortality. To assess mortality risk in patients suffering from VCF, we conducted a retrospective observational long-term cohort study. The study included 270 patients. 221 patients were treated conservatively, and 49 were treated with vertebroplasty. The study group was compared to a control group of 1641 random individuals age and sex-matched. Electronic healthcare data extracted included monthly chronic medications taken regularly 3months before hospitalisation, analgesics excluded, and date of death. Patients who suffer from VCF tend to consume more chronic medications. The mean count of chronic medication prescriptions in the 3months before hospitalisation was 16.41 (±9.11) in the VCF group and 11.52 (± 7.17) in the control cohort (P < .0001). In univariate analysis, patients with VCF showed decreased long-term survival (P < .00). However, when controlled for age, sex, and chronic medications uptake, no significant difference was observed between the groups in a multivariate model (P = .12). The study demonstrates that VCF as an independent variable has a marginal effect on mortality. The higher mortality prevalent in these patients is due to the deteriorated health status of the patients before fracture.

Numerical modeling of open TBM tunneling in stratified rock masses using a coupled FDM-DEM method

The complex engineering characteristics of stratified rock masses make the comprehensive analysis of TBM tunneling more complex and difficult. In this study, an advanced modeling method based on the coupled finite difference method (FDM) and discrete element method (DEM) was proposed for the simulation of open TBM tunneling in stratified rock masses. The modeling and analysis process of the FDM-DEM numerical model was presented with the DLS Tunnel as the research background. Numerical results show that the displacement values and characteristics of the rock mass are consistent with the deformation of the surrounding rocks obtained from in situ monitoring. Severe shear and tensile fractures occur progressively in both rock blocks and bedding planes during TBM tunneling. The extent of the loosening area in the rock mass also continues to grow. The numerical model reproduces the progressive failure process of the stratified rock mass through the analysis of contact fracture events and the evolution of contact forces. The simulation of the interaction between the rock mass and the shield is accomplished by FDM-DEM coupling methods under the large-strain mode. This study presents an effective tool for the comprehensive analysis of open TBM tunneling in stratified rock masses.

Making sense of brittle deformation in rhyolitic lavas: Insights from Obsidian Dome, California, USA

AbstractThe scarcity of observed active extrusive rhyolitic lava flows has skewed research to extensively focus on prehistoric lavas for information about their eruptive and emplacement dynamics. The first ever witnessed silicic lava eruptive events, Chaitén (2008) and Cordón Caulle (2011–2012) in Chile, were illuminating to the volcanology community because they featured a range of emplacement processes (endogenous versus exogenous), movement limiting modes, and eruptive behaviors (explosive versus effusive) that were often regarded as acting independently throughout an eruptive event. In this study, we documented evidence of a continuum of brittle and brittle-ductile deformation and fracture-induced outgassing during the emplacement of the ~600-yr-old silicic lava from Obsidian Dome, California, USA. This study focused on mapping the textural-structural relationships of the upper surface of the lava onto high-resolution (&amp;lt;10 cm2/pixel) orthorectified color base maps. We found that the upper surface is characterized by small (&amp;lt;1 m) mode 1 tensile fractures that grew and initiated new cracks, which linked together to form larger tensile fractures (1–5 m), which in turn penetrated deeper into the lava. We recorded ornamentations on these fracture surfaces that allow snapshot views into the rheological and outgassing conditions during the lava’s effusion. The largest fractures developed during single, large fracture events in the final stages of the lava’s emplacement. Ornamentations preserved on the fractured surfaces record degassing and explosive fragmentation away from the vent throughout the lava’s emplacement, suggesting explosive activity was occurring during the effusive emplacement. Field-based cataloguing of the complexities of fracture surfaces provides qualitative constraints for the future mechanical modeling of effusive lavas.

Conventional androgen deprivation therapy is associated with an increased risk of fracture in advanced prostate cancer, a nationwide population-based study.

Androgen deprivation therapy (ADT) is the standard of care in advanced prostate cancer. We conducted a Taiwan National Health Insurance Research Database (NHIRD) study to evaluate the association between ADT and fracture risk in patient with prostate cancer in Taiwan. Between 2001 and 2008, data from the Taiwan NHIRD was collected. We separated newly diagnosed prostate cancer patients into four groups: the injection of gonadotropin-releasing hormone agonists and antagonists group, the orchiectomy group, the oral antiandorgens group and the radical prostatectomy only group. A non-cancer matched control group was also assigned for comparison. T tests, chi-squared tests, multivariate Cox proportional hazard regression were performed. A subsequent fracture event was defined according to the appropriate diagnosis codes (ICD9-CM 800-829) with hospitalization. Patients with fracture before their diagnosis with prostate cancer were excluded. Overall, 22517 newly diagnosed patients with prostate cancer were enrolled in the study. After exclusion criteria were applied, 13321 patients were separated into the injection group (5020 subjects), the orchiectomy group (1193 subjects), the oral group (6059 subjects) and the radical prostatectomy only group (1049 subjects). The mean age of the overall study population was 74.4 years. Multi-variant analysis disclosed a significantly increased risk of fracture in the injection group, the orchiectomy group, and the oral group (hazard ratio [HR] = 1.55, 95%, confidence interval [CI] 1.36 to 1.76, p<0.001, HR = 1.95, 95%, CI 1.61 to 2.37, p<0.001, HR = 1.37, 95%, CI 1.22 to 1.53, p<0.001, respectively). In contrast, a significantly decreased fracture risk was noted in the radical prostatectomy only group (HR = 0.51, 95%, CI 0.35 to 0.74, p = 0.001). Patients receiving osteoporosis medication had a significantly decreased fracture risk (HR = 0.26, 95%, CI 0.19-0.37, p<0.001). ADT is associated with an increased risk of fracture. For patients receiving long-term prostate cancer castration therapy, doctors should always keep this complication in mind and arrange proper monitoring and provide timely osteoporosis medication.

Importance of Whole-Body Scintigraphy or Positron Emission Tomography for Early Detection of Femoral Lesions in Breast Cancer Patients Treated with Bisphosphonates.

We hypothesized that most of the atypical femoral fractures (AFFs) associated with bisphosphonate treatment for breast cancer (BC) could be found before the fracture event in another radiological examination already performed by breast surgeons, rather than on simple radiographs (SRs). We thoroughly inspected the clinical charts of BC patients treated at our institute between 2008 and 2017. In total, 228 patients were categorized into three groups based on SRs: complete AFF on at least one side (group 1); incomplete fracture on at least one side, but not any complete fracture (group 2); and no suspicious lesion (group X) on either femur. Then, we inspected whole-body scintigraphy (WBS) and positron emission tomography (PET)-computed tomography (CT) images in all groups. For group X, patients with radiological clues from at least one femur were categorized, ultimately, into final group 3 and the rest made up the normal group. About 35% of the patients showed AFFs (complete or incomplete) or suspicious lesions as AFFs, associated with the side effect of Bisphosphonate. In group 1, bilateral lesions (complete or incomplete fractures) were more frequently seen on SRs than unilateral lesions (p = 0.008). The initially identified findings in WBS and PET-CT for the respective complete and incomplete fractures on SRs of groups 1 and 2 were seen at a mean of 7 months previously. SRs did not reveal the lesions in group 3 until 5 months after the initial identification of the lesions in WBS and PET-CT. Even before incomplete AFFs were detectable on SRs, they could be found at check-ups using WBS and PET-CT that had been previously examined by breast surgeons and radiologists for metastasis surveillance. Awareness of the lesions creates an opportunity for prophylactic surgery before complete fractures occur.

AN ANISOTROPIC EXTENSION FOR A THERMOVISCOPLASTIC GTN DUCTILE DAMAGE MODEL

In this work, a thermoviscoplastic GTN ductile damage model is extended to account for anisotropic plastic behavior. The novel feature of the proposed model is the enrichment of a GTN model, with the Hill's yield criterion accounting for hardening, softening, strain-rate effect, plastic work heating, thermal diffusion, and void shearing mechanism. The anisotropy is introduced by changing the equivalent stress definition, which provides greater flexibility to the model. The resultant modifications in the yield criterion and in the damage evolution equations are described. Two numerical problems involving plates subjected to tension loading that leads to ductile damage and eventual fracture are presented and discussed in order to validate the present approach. A mixed finite element formulation is adopted together with the fully damaged zone technique to represent the ductile fracture. Results obtained through computational simulations highlight the effect of the anisotropic parameters on mechanical behavior in terms of the global stress-strain curve and the local evolution of plastic strains, porosity and temperature. We conclude that the proposed anisotropic model is simple to implement yet provides more flexibility in capturing complex ductile fracture processes.

Micromechanical characterisation of overburden shales in the Horn River Basin through nanoindentation

The paper presents a micromechanical characterisation of Fort Simpson shale, which overlies unconventional gas-producing lithologies in the Horn River Basin, NW Canada. The Fort Simpson formation is clay-rich and microseismic data recorded during hydraulic fracturing events in the underlying reservoir has shown the formation acts as a barrier to fracture development, with a notably anisotropic seismic response. Samples were prepared from core fragments and the composition and texture of the shale was characterised using X-ray diffraction, mercury injection porosimetry and scanning electron microscopy (SEM). Nanoindentation testing was used to obtain the mechanical response of the shale microstructure, at grain-scale. The indentation was conducted on a grid pattern and samples were oriented both parallel and perpendicular to the bedding plane to assess the inherent mechanical anisotropy. Chemical analysis of the grids was also undertaken through SEM/EDS (energy dispersive X-ray spectroscopy) and the coupled chemo-mechanical data was used to characterise the material phases of the shale through a statistical clustering procedure. The results show that Fort Simpson shale broadly consists of a soft clay phase, with strongly anisotropic elastic stiffness, and stiffer but effectively isotropic grains of quartz and feldspar. A simple upscaling scheme was also applied to link the grain-scale elastic stiffness to the field-scale microseismic data.

Multiphase deformation, fluid flow and mineralization in epithermal systems: Inferences from structures, vein textures and breccias of the Kestanelik epithermal Au-Ag deposit, NW Turkey

We investigate the multiphase deformation, fluid flow, and mineralization processes in epithermal systems by presenting a detailed study of vein textures and breccias of the Kestanelik epithermal Au-Ag deposit, NW Turkey. The mineralization in the deposit is associated with several quartz veins. Fault-hosted veins and mode I veins share many textural and breccia characteristics owing to (i) overprinting of tectonic breccias formed during coseismic rupturing by subsequent coseismic hydrothermal brecciation and (ii) reworking of earlier vein breccia phases by repeated rupturing and hydraulic fracturing events. The spatial distribution of breccias at fault-hosted veins proposes that power of coseismic hydrothermal brecciation is controlled by the distance to the level of boiling within a vein. The brecciation affects the entire vein proximal to the level of boiling; however, it is limited to the footwall contact of the vein more distally at the upper levels of a vein. Varying number of mineralization events for the veins suggests that any individual earthquake event reopened only one or more sealed vein, but not all at once. Fewer mineralization events in fault-hosted veins compared to the mode I veins is either linked to (i) focusing of high fluid flux into the conduits of mode I veins that accommodate more dilation or (ii) reopening of mode I veins owing to the driven of extensional failure under low differential stress. Although fault-hosted veins record fewer mineralization events, they have higher average Au grade (4.106 g/t) compared to that of mode I veins (2.736 g/t). On the other hand, fewer mineralization events in wall rock structures compared to the adjacent faults is attributed to (i) absence or poor development of the damage zone structures in earlier seismic events or (ii) deactivation of them after clogging due to the rotation of the optimum stress field or (iii) their formation as hydraulic extension fractures. This study emphasizes the importance of detailed studies of vein infill for understanding the internal structural evolution of the veins in epithermal deposits that is interest to the geologists within both industry and academic fields.

Fractographic analysis of fractured fixation screws in implant-supported restorations.

The aim of this study was to fractographically examine clinically fractured fixation screws used to fix implant supported restorations and to estimate stress at failure. 20 clinically fractured titanium implant fixation screws were collected and analyzed under scanning electron microscope in order to locate critical crack origin and calculate stress at fracture. Principles of fractographic analysis were applied using relative equations and cause and conditions of screw fracture were calculated. X-rays and patients' records were collected after approval of necessary consent forms. Fractographic analysis revealed location and dimensions of critical crack size for every fractured screw examined. Two patterns of screw fracture were identified; the first was related to improper seating of fixation screw leading to damage at screw threads and eventual fracture of screw body. The second was related to slow crack growth propagation causing final fracture of screw body. The calculated stress at failure ranged from 755 to 804MPa. Patients' records revealed that 75% of fractured screws were related to single unit screw retained restorations. Single unit screw retained restorations and improperly seated implant abutments impose high stress concentration on fixation screw which may result in fixation screw fracture.

Birefringence analysis of aluminum-to-BK7 bonding methods under thermal stress

Ultrafast laser welding, hydroxide catalysis bonding (HCB) and adhesive bonding techniques were used to bond N-BK7 cubes to aluminum bases. Using a thermal chamber and polariscope, the stress induced birefringence was measured at temperatures from -50°C to +80°C. Adhesive samples made with different industrial assembly methods were compared for thermal birefringent behavior. An ultrafast laser welded sample was thermally cycled in increasing temperature ranges, surviving the test with reduced retardation, indicating fatigue. An HCB sample was thermally cycled like the laser welded sample, and had a linear birefringent relation to temperature initially, and failed by fatigue after a fracture event.

Efficacy and safety of pharmacologic therapies for prevention of osteoporotic vertebral fractures in postmenopausal women

BackgroundThere are many pharmaceutical interventions available to prevent osteoporotic vertebral fractures in postmenopausal women, but the efficacy and safety of these drugs are unknown. This study aimed to investigate the efficacy and safety of drugs in the prevention of osteoporotic vertebral fractures. MethodsPubMed, Embase, and the Cochrane Library were comprehensively searched for randomized controlled trials (RCTs) published up to February 15, 2020, including postmenopausal women with osteoporosis. Network meta-analysis was conducted based on the Cochrane Handbook for Systematic Reviews of Interventions and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The relative risk (RR) and 95% confidence interval (CI) were used to report the results. This study was registered with PROSPERO, number CRD42020201167. Main Outcomes were incidences of new vertebral fracture and serious adverse events. ResultsFifty-five RCTs (n = 104 580) evaluating vertebral fractures of sixteen kinds of pharmacologic therapies were included in the network meta-analysis. Abaloparatide (RR, 0.21; [95% CI, 0.09 to 0.51]), alendronate (RR, 0.55; [95% CI, 0.38 to 0.81]), calcitonin (RR, 0.44; [95% CI, 0.25 to 0.78]), denosumab (RR, 0.33; [95% CI, 0.14 to 0.61]), parathyroid hormone (PTH) (RR, 0.32; [95% CI, 0.10 to 0.97]), risedronate (RR, 0.65; [95% CI, 0.42 to 1.00]), romosozumab (RR, 0.31; [95% CI, 0.16 to 0.61]), strontium ranelate (RR, 0.62; [95% CI, 0.42 to 0.93]), teriparatide (RR, 0.27; [95% CI, 0.17 to 0.43]), and zoledronate (RR, 0.41; [95% CI, 0.93]) were associated with lower vertebral fracture risk compared to placebo. PTH was associated with more adverse event rates. For any two drug treatments, the RR of serious adverse events was not statistically significant. Hormone replacement therapy (HRT) and calcitonin may be slower to work because they have only been shown to reduce the risk of vertebral fractures in long-term (>18 months) follow-up. ConclusionsA variety of drugs are safe and effective in preventing osteoporotic vertebral fractures. HRT and calcitonin only reduced the risk of vertebral fractures during a follow-up of 21–72 months.

The Ediacaran Hiyam Formation: A zoom through the diagenetic and structural complexity of the metamorphic Hi2 Member, Saih Hatat Dome, Oman Mountains

This is the first diagenetic study of the metamorphic upper Hiyam Member “Hi2” of the Saih Hatat Dome. Despite metamorphism, texture and paragenesis of the Hi2 Member are so well preserved that it is possible to unravel its diagenetic evolution. We applied lithological and structural field methods, transmission and cathodoluminescence microscopy to establish the paragenetic sequence and vein-forming deformation. Our work reveals a complex diagenetic and structural history, including several alternating dolomitization, calcite precipitation, silicification and fracturing events. Most of the replacive dolomite and silica are linked to early diagenesis under intertidal to sabkha and restricted marine as well as to terrestrial conditions. Evaporation of sea water concentrated Mg2+ and triggered extensive early dolomitization while silica-bearing fluids caused local silicification. Various generations of dolomite and calcite cements pervasively occluded macropores, micropores and veins. Late burial is reflected by pressure solution seams/stylolites, non-ferroan to weakly ferroan saddle-type dolomite cement and non-ferroan blocky and drusy calcite cement, filling veins and macropores. The various generations of calcite cements (e.g., in veins) are considered to have formed during burial or possibly meteoric conditions. The latter potentially resulted from tectonic uplift, while late dolomite cement displays hydrocarbon residues from coeval oil migration. A later minor oil migration event has also been recognized. Initial fracture/fissure formation is most likely related to folding during the Early Cambrian Angudan Orogeny (open NW-SE fractures) and to divergence during the Late Paleozoic Pangean/Neo-Tethys rifting (open NW-SE fractures). Metamorphism impacted the Hi2 Member, resulting in phyllite formation, phyllosilicate crystallization and ductile shearing. Metamorphism occurred during shallow Late Cretaceous subduction. Striking lithological similarities between the Hi2 Member and that of the upper Kharus Formation of the Jabal Akhdar region could indicate their lateral equivalence.

Urinary and Daily Assumption of Polyphenols and Hip-Fracture Risk: Results from the InCHIANTI Study.

A high polyphenol intake has been associated with higher bone-mineral density. In contrast, we recently demonstrated that the urinary levels of these micronutrients were associated with the long-term accelerated deterioration of the bone. To expand on the health consequences of these findings, we assessed the association between urinary level and dietary intake of polyphenols and the 9-year risk of hip fractures in the InCHIANTI study cohort. The InCHIANTI study enrolled representative samples from two towns in Tuscany, Italy. Baseline data were collected in 1998 and at follow-up visits in 2001, 2004, and 2007. Of the 1453 participants enrolled at baseline, we included 817 participants in this study who were 65 years or older at baseline, donated a 24 hour urine sample, and underwent a quantitative computerized tomography (pQCT) of the tibia. Fracture events were ascertained by self-report over 9 years of follow-up. Thirty-six hip fractures were reported over the 9-year follow-up. The participants who developed a hip fracture were slightly older, more frequently women, had a higher dietary intake of polyphenols, had higher 24-hour urinary polyphenols excretion, and had a lower fat area, muscle density, and cortical volumetric Bone Mineral Density (vBMD) in the pQCT of the tibia. In logistic regression analyses, the baseline urinary excretion of total polyphenols, expressed in mg as a gallic acid equivalent, was associated with a higher risk of developing a hip fracture. Dietary intake of polyphenols was not associated with a differential risk of fracture. In light of our findings, the recommendation of an increase in dietary polyphenols for osteoporosis prevention should be considered with caution.

Adiabatic Shear Banding in Nickel and Nickel-Based Superalloys: A Review

This review paper discusses the formation and propagation of adiabatic shear bands in nickel-based superalloys. The formation of adiabatic shear bands (ASBs) is a unique dynamic phenomenon that typically precedes catastrophic, unpredicted failure in many metals under impact or ballistic loading. ASBs are thin regions that undergo substantial plastic shear strain and material softening due to the thermo-mechanical instability induced by the competitive work hardening and thermal softening processes. Dynamic recrystallization of the material’s microstructure in the shear region can occur and encourages shear localization and the formation of ASBs. Phase transformations are also often seen in ASBs of ferrous metals due to the elevated temperatures reached in the narrow shear region. ASBs ultimately lead to the local degradation of material properties within a narrow band wherein micro-voids can more easily nucleate and grow compared to the surrounding material. As the micro-voids grow, they will eventually coalesce leading to crack formation and eventual fracture. For elevated temperature applications, such as in the aerospace industry, nickel-based superalloys are used due to their high strength. Understanding the formation conditions of ASBs in nickel-based superalloys is also beneficial in extending the life of machining tools. The main goal of the review is to identify the formation mechanisms of ASBs, the microstructural evolutions associated with ASBs in nickel-based alloys, and their consequent effect on material properties. Under a shear strain rate of 80,000 s−1, the critical shear strain at which an ASB forms is between 2.2 and 3.2 for aged Inconel 718 and 4.5 for solution-treated Inconel 718. Shear band widths are reported to range between 2 and 65 microns for nickel-based superalloys. The shear bands widths are narrower in samples that are aged compared to samples in the annealed or solution treated condition.

Discrete Element Modelling of Cold Crushing Tests Considering Various Interface Property Distributions in Ordinary Refractory Ceramics.

The microstructures and local properties of ordinary refractory ceramic materials are heterogeneous and play a role in the fracture behavior of ordinary refractory ceramic materials. It is important to consider them in numerical modeling. Herein, the discrete element (DE) method was applied to determine the influences of heterogeneity of ordinary refractory ceramic materials by applying statistically distributed interface properties (uniform, Weibull), as opposed to constant interface properties, among the elements. Uniaxial cold crushing tests were performed as a case study. A reasonable loading strain rate for receiving quasi-static loading conditions and computation efficiency was evaluated. The loading wall displacement was recorded to present the stress-strain curves of cold crushing tests. Furthermore, the effects of the interface property distributions on the load/displacement curve, fracture energy, cold crushing strength, and fracture events were investigated. The results reveal that the DE method is a promising method for visualizing and quantifying the post-peak fracture process and crack events in ordinary refractory ceramics. Different interface property distributions contribute to significant variances in the load/displacement curve shape and fracture pattern. The heterogeneity of ordinary refractory ceramics can be further determined by comparing the experimental curves and fracture propagation along with an inverse identification approach.

Wave-triggered breakup in the marginal ice zone generates lognormal floe size distributions: a simulation study

Abstract. Fragmentation of the sea ice cover by ocean waves is an important mechanism impacting ice evolution. Fractured ice is more sensitive to melt, leading to a local reduction in ice concentration, facilitating wave propagation. A positive feedback loop, accelerating sea ice retreat, is then introduced. Despite recent efforts to incorporate this process and the resulting floe size distribution (FSD) into the sea ice components of global climate models (GCMs), the physics governing ice breakup under wave action remains poorly understood and its parametrisation highly simplified. We propose a two-dimensional numerical model of wave-induced sea ice breakup to estimate the FSD resulting from repeated fracture events. This model, based on linear water wave theory and visco-elastic sea ice rheology, solves for the scattering of an incoming time-harmonic wave by the ice cover and derives the corresponding strain field. Fracture occurs when the strain exceeds an empirical threshold. The geometry is then updated for the next iteration of the breakup procedure. The resulting FSD is analysed for both monochromatic and polychromatic forcings. For the latter results, FSDs obtained for discrete frequencies are combined following a prescribed wave spectrum. We find that under realistic wave forcing, lognormal FSDs emerge consistently in a large variety of model configurations. Care is taken to evaluate the statistical significance of this finding. This result contrasts with the power law FSD behaviour often assumed by modellers. We discuss the properties of these modelled distributions with respect to the ice rheological properties and the forcing waves. The projected output can be used to improve empirical parametrisations used to couple sea ice and ocean wave GCM components.

A study on moment tensor inversion of acoustic emission response on damaging localization of gas-bearing coal under load

During the deformation and fracture process, the acoustic emission (AE) signals can be produced for the of coal, rock and other solid materials, which revealing the damage localization evolution process. The effect of gas adsorption and pressure can change mechanical properties of coal mass and affect its damage development. Based on this, the experimental system for gas-bearing coal loading and AE monitoring was constructed, to analyze AE response characteristics under the joint action of loading stress and gas pressure on coal specimen. Afterwards, the damage localization evolution process of coal mass was studied with the moment tensor inversion method. Results showed that temporal response of AE signals was closely related to the damage degree and loading level of coal specimen, which could reveal its local severe damage and final failure characteristics. The spatial distribution and spread trend of AE fracture events inside coal specimen could be calculated through the moment tensor inversion method. It was basically consistent with the results of crack expansion on the specimen surface. The zones, where fracture events occurred intensively, gathered and spread in a continuous trend, were conductive to forming the macrocrack belt macroscopically. It could be regarded as the hazard zone with dynamic failure occurrence. Moreover, when the coal specimen faced the critical failure, the precursor characteristics of AE response appeared with the shear fracture events dominated markedly. The study results provide a new research idea for revealing the damaging localization evolution process under the coupling effect of stress and gas and lay the application foundation.