Fracture Appearance Research Articles

Mechanical behaviour and acoustic emission characteristics of basalt fibre mortar rubble under uniaxial cyclic compression

To investigate the effect of basalt fibre (BF) content on the mechanical behaviour and damage characteristics of mortar rubble under cyclic loading, uniaxial compression tests and cyclic loading and unloading tests were carried out on specimens fabricated with different BF volume fractions. Based on damage mechanics theory, a damage ontology model of BF mortar rubble was developed. The damage of BF mortar rubble under cyclic loading was identified and analysed using acoustic emission (AE) techniques, and parameters such as the Felicity ratio (FR), ratio of the RA (rise time/amplitude) and the average frequency (RA/AF), response ratio, b-value and peak frequency were used to characterise the failure mechanism of BF mortar rubble. The results of this study revealed that the incorporation of BF increased the compressive strength by 9.3%-14.2%. The response ratios of the initial cycles were 91.2, 53.4 and 24.4 when the BF content was 0.2%, 0.3% and 0.4% respectively. The incorporation of BF helps to delay the onset of critical damage values. The peak frequency signals are concentrated in the region of 50 kHz and 160 kHz. the 50 kHz frequency represents the appearance of fractures in the matrix and the 160 kHz frequency signal represents the occurrence of brittle fractures in the aggregate. The FR trend was a good predictor of damage to the mortar rubble. The damage mode of the mortar rubble changed from tensile fracturing to composite fracturing due to the addition of BF. The performance optimisation concept of mortar rubble proposed in this study provides a reference for the optimal design of BF mortar rubble and thus has a strong application value.

Experimental Study on the Charge Signal Time-Frequency Characteristics during Fracture Process of Precracked Syenogranite under Uniaxial Compression

During the process of rock deformation and failure, a significantly large number of charge signals are generated as a result of fracture appearance and crack expansion. The generation of charge signal is the comprehensive embodiment of the coal-failure behavior. The study of charge signal in the process of fractured-rock deformation and failure is of great significance to the prediction of rock dynamic disasters such as tunnel-engineering stability, slope instability and earthquake. In this work, a surveillance system utilizing charge induction is employed to extract precursory information related to the instability and failure of precracked syenogranite. The results reveal a significant influence of fractures on the strength of syenogranite specimens and the number of charge-induction signal events. The position of the charge signal generated is related to the crack dip angle. Furthermore, with the increase of the crack inclination, the number of events and the amplitude and power value of the charge-induced signal increase and reach the maximum in the instability-failure phase. The syenogranite specimen has a relatively large value, medium correlation, or even high correlation charge-induction signal in the phase of rack propagation, which can make an early warning of the deformation and failure risk of syenogranite; with the increase of the fracture degree, the charge-induction signal with large values and high correlations gradually increases.

Using video detection of snow surface movements to estimate weak layer crack propagation speeds

Abstract Dry-snow slab avalanches release due to crack propagation in a weak snow layer under a cohesive snow slab. Crack propagation speeds can provide insights into the potential size of avalanches and inform fracture and avalanche release models. Despite their importance, slope-scale crack speed measurements from real avalanches are limited. Further, most existing slope-scale measurements utilize the appearance of slab fractures on the snow surface. However, we have no evidence that the appearance of surface cracking is a good indicator of the weak layer crack propagation tip. Here we present a novel method to estimate crack propagation speed from snow surface movements in avalanche videos. Our technique uses changes in frame pixel intensity, allowing us to detect the location of weak layer cracks well before slab fractures appear on the snow surface. We use field experiments and numerical simulations to validate our method before applying it to five avalanches. Our estimates show that cracks propagate faster up and down the slope than in the cross-slope direction; this suggests that different propagation regimes likely govern crack propagation up/down the slope, cross-slope and in flat terrain.

Variation in radial head fracture treatment recommendations in terrible triad injuries is not influenced by viewing two-dimensional computed tomography.

We analyzed association between viewing two-dimensional computed tomography (2D CT) images in addition to radiographs with radial head treatment recommendations after accounting for patient and surgeon factors in a survey-based experiment. One hundred and fifty-four surgeons reviewed 15 patient scenarios with terrible triad fracture dislocations of the elbow. Surgeons were randomized to view either radiographs only or radiographs and 2D CT images. The scenarios randomized patient age, hand dominance, and occupation. For each scenario, surgeons were asked if they would recommend fixation or arthroplasty of the radial head. Multi-level logistic regression analysis identified variables associated with radial head treatment recommendations. Reviewing 2D CT images in addition to radiographs had no statistical association with treatment recommendations. A higher likelihood of recommending prosthetic arthroplasty was associated with older patient age, patient occupation not requiring manual labor, surgeon practice location in the United States, practicing for five years or less, and the subspecialties "trauma" and "shoulder and elbow." The results of this study suggest that in terrible triad injuries, the imaging appearance of radial head fractures has no measurable influence on treatment recommendations. Personal surgeon factors and patient demographic characteristics may have a larger role in surgical decision making. Level of evidence: Level III, therapeutic case-control study.

Fracture risk after deprescription of bisphosphonates: Application of real-world data in primary care

PurposeTo compare the effect of discontinuing bisphosphonate treatment on fracture risk in postmenopausal women at high versus low risk of fracture. DesignRetrospective, longitudinal and population-based cohort study. SettingBarcelona City Primary Care. Catalan Health Institute. ParticipantsAll women attended by primary care teams who in January 2014 had received bisphosphonate treatment for at least five years were included and followed for another five years. InterventionPatients were classified according to their risk of new fractures, defined as those who had a history of osteoporotic fracture and/or who received treatment with an aromatase inhibitor, and the continuity or deprescription of the bisphosphonate treatment was analyzed over fiver year follow-up. Main measurementsThe cumulative incidence of fractures and the incidence density were calculated and analyzed using logistic regression and Cox models. ResultsWe included 3680 women. There were no significant differences in fracture risk in high-risk women who discontinued versus continued bisphosphonate treatment (hazard ratio [HR] 1.17, 95% confidence interval [CI] 0.87–1.58 for total osteoporotic fractures). However, discontinuers at low risk had a lower incidence of fracture than continuers. This difference was significant for vertebral fractures (HR 0.64, 95% CI 0.47–0.88) and total fractures (HR 0.77, 95% CI 0.64–0.92). ConclusionOur results suggest that deprescribing bisphosphonates in women who have already received five years of treatment does not increase fracture risk. In low-risk women, continuing this treatment might could even favor the appearance of new osteoporotic fractures.

In-situ damage monitoring and numerical characterization of three-point bending and incremental cycle flexural behavior of FMLs

This article experimentally and numerically investigates the bending response and failure mechanisms of FMLs under three-point bending tests. The in-situ microscope observation from step-by-step interrupted flexural tests is implemented to capture the failure mechanisms and damage evolution. Then, a numerical simulation is employed to characterize the damage initiation and progressive damage evolution process. Finally, the bending response and stiffness degradation of FMLs under incremental cyclic flexural loading tests are experimentally researched. The in-situ monitoring for FMLs-A shows that the appearance of fiber kink-band, fiber fracture, and metal cracking are identical with the moments of sudden loading decrease, respectively.

Correction to: Ultrasonic-Assisted Fracture Appearance of Titanium

Correction to: Ultrasonic-Assisted Fracture Appearance of Titanium

Ultrasonic-Assisted Fracture Appearance of Titanium

Ultrasonic-Assisted Fracture Appearance of Titanium

Effect of heat treatment on the microstructure, impact toughness and wear resistance of Fe-based/B4C composite coating by vacuum cladding

The study focused on the effect of quenching and quenching-tempering processes on the microstructure, hardness, impact toughness and wear resistance of Fe-based/B4C composite coating on the surface of ASTM 1045 steel by vacuum cladding. The results revealed that the metallurgical bonding was realized between the coating and steel substrate. After quenching at 950/1000/1050 °C and quenching-tempering at 1000–490/1000–540/1000–590 °C, the hard phases (M2B and M23 (C, B) 6) in the coating remained unchanged in type, but their morphologies were broken and became more rounded. The coating matrix changed from pearlite to martensite, and granular secondary phases of M23(C, B)6 precipitated from coating matrix. After heat treatment, the impact energy of coated samples is significantly improved, which may be related to the evolution of the coating microstructure and the appearance of interfacial delamination fracture. The results of the wear test showed that the change of coating matrix and hard phase morphology, and the coordination between them were the main factors affecting the wear resistance of the coating. The best wear resistance of the coating was obtained at QT540, and the wear mechanisms were mainly fatigue spalling and brittle fracture.

Fatigue Life Testing of the Round Link Mining Chains

Abstract The material fatigue phenomenon consists of progressive material damage through the appearance and development of fractures under the influence of variable, periodically recurring stresses. Engineers designing machinery and structures to be fatigue resistant can gain useful insights about design and material properties by reviewing the literature. In this way, we can avoid costly research, but in the case of complex loading phenomena and the interaction of components, we must carry out such research. Fatigue strength calculations are less accurate than simple static calculations. The wear of link chains is concentrated in three areas, depending on the installation location and function of the individual links, namely: in the joints (the points of contact between two links), on the outer surfaces of the arches and on the outer surfaces of the straight sections of the links. During operation, chains are particularly vulnerable to wear through abrasion, corrosion and fatigue. These ageing factors, which act with varying intensity depending on the properties of the deposit, determine the service life of the chain, unless other unforeseen damage occurs, e.g. "hard" blockage of the chain. In many cases, users are guided by their own subjective criteria for assessing the technical condition of chains, which does not always lead to fully rational decisions regarding the continued use of used chains. To date, there have been no attempts to transfer the results of chain fatigue tests to behaviour of real objects. This paper presents issues related to mining chain fatigue testing. The test results presented are for both new and used chains. The experimental tests conducted at GIG made it possible to solve the problem of applying fatigue test results in industrial practice.

Effects of Micro-Shot Peening on the Fatigue Strength of Anodized 7075-T6 Alloy.

Micro-shot peening under two Almen intensities was performed to increase the fatigue endurance limit of anodized AA 7075 alloy in T6 condition. Compressive residual stress (CRS) and a nano-grained structure were present in the outermost as-peened layer. Microcracks in the anodized layer obviously abbreviated the fatigue strength/life of the substrate. The endurance limit of the anodized AA 7075 was lowered to less than 200 MPa. By contrast, micro-shot peening increased the endurance limit of the anodized AA 7075 to above that of the substrate (about 300 MPa). Without anodization, the fatigue strength of the high peened (HP) specimen fluctuated; this was the result of high surface roughness of the specimen, as compared to that of the low peened (LP) one. Pickling before anodizing was found to erode the outermost peened layer, which caused a decrease in the positive effect of peening. After anodization, the HP sample had a greater fatigue strength/endurance limit than that of the LP one. The fracture appearance of an anodized fatigued sample showed an observable ring of brittle fracture. Fatigue cracks present in the brittle coating propagated directly into the substrate, significantly damaging the fatigue performance of the anodized sample. The CRS and the nano-grained structure beneath the anodized layer accounted for a noticeable increase in resistance to fatigue failure of the anodized micro-shot peened specimen.

Pregnancy and Lactation-Associated Osteoporosis Successfully Treated with Romosozumab: A Case Report

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare type of premenopausal osteoporosis that occurs mainly in the third trimester or immediately after delivery; one of its most common symptoms is back pain caused by a vertebral fracture. The pathogenesis of PLO is unclear, and there is no accepted consensus regarding the treatment of PLO. Although treatments with drugs such as bisphosphonate, strontium ranelate, denosumab, and teriparatide were reported, there is no report of a patient with PLO treated with romosozumab. We present the first case of a patient with PLO treated with romosozumab following 4-month teriparatide treatment. A 34-year-old primiparous and breastfeeding Japanese woman experienced severe low back pain 1 month postdelivery. She was diagnosed with PLO on the basis of low bone marrow density (BMD) and multiple vertebral fractures with no identified cause of secondary osteoporosis. She was treated with teriparatide injection for 4 months, but the treatment was discontinued because of the patient feeling severe nausea after every teriparatide injection and the appearance of new vertebral fractures. Thereafter, we used romosozumab for 12 months. After the romosozumab treatment, her BMD was increased from the baseline by 23.6% at L1-L4, 6.2% at the femoral neck, and 11.2% at the total hip. Treating PLO with 12-month romosozumab after 4 months of teriparatide injection remarkably increased the BMD of the lumbar spine, femoral neck, and total hip without subsequent fracture. Romosozumab has potential as a therapeutic option to improve the BMD and reduce the subsequent fracture risk of patients with PLO.

Effect of Notch Structure and Notch Bottom Diameter on the Tensile Load of a Certain GH4169 Notch Bolt for a Device for Longitudinal Separation of Fairing

The effect of the notch structure and bottom diameter of a GH4169 notch bolt for an explosive separation device used for longitudinal separation of the fairing, and GH4169 strength range on the tensile load was studied by combing simulations with tests. The results show that the V-shaped, arc-shaped and square notch structures can improve the tensile load of the bolt but to a lesser degree in sequence, and the arc-shaped notch structure performs best in terms of tensile load, fracture appearance and shear resistance. In order to meet the design requirements of 14–15.5 KN tensile load for the notch bolt with an arc-shaped structure, four raw material tensile intervals corresponding to the notch bottom diameters were established by using domestic GH4169 grade C cold-drawn bars.

Accelerated damage mechanisms of aluminized superalloy turbine blades regarding combined high-and-low cycle fatigue

Accelerated fatigue failure mechanisms of aluminized Ni-based superalloy turbine blades are the focused in this paper. The qualitative and quantitative analyses on the fracture appearances and microstructures of the field-serviced and lab-tested turbine blades were conducted, and a ‘micro-defect transfer mechanism’ is finally raised and elucidated regarding the combined high-and-low cycle fatigue (CCF). The CCF tests are performed on the Ni-based superalloy turbine blades with aluminized coatings in three acceleration states. Then, the fracture morphologies are inspected to confirm the dominant sources of crack initiations under different accelerated loads. It illustrates that: the cracks mainly generate from the interface in the slow acceleration state, which is similar to that in the service state. While, the surface and interface cracking collaborates in the fast acceleration state, as the surface cracking turning to be the dominant factor. Furthermore, to interpret the essential mechanisms of fatigue failures of the aluminized turbine blades, the qualitative and quantitative analyses are carried out on the cross-sectional microstructures and elemental compositions jointly assisted by advanced intelligent algorithms, which can assist to better identify and extract the valid information in the microscopic images. Ultimately, the micro-defect transfer mechanism is proposed and elaborated in detail for revealing the fatigue failure mechanisms of aluminized turbine blades in different acceleration states.

Experimental study on seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill with defects

In order to study the seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill (CGFB) with defects, the samples of single crack CGFB with different angles were prepared and the triaxial compression test under seepage conditions was carried out. The effects of seepage pressure and crack defects on the seepage-stress coupling failure characteristics of CGFB were analyzed. In addition, the box dimension method was introduced to calculate the fractal dimension, so as to quantitatively characterize the correlation between fracture morphology and mechanical properties. The results show that: 1) the permeability and acoustic emission change periodically with the stress-time curve during the deformation and failure of CGFB. With the increase of seepage pressure, the characteristic permeability of CGFB increases, and the characteristic permeability of CGFB with defects is higher than that of intact CGFB. 2) Under the seepage-stress coupling, there is no obvious corresponding relationship between the fractal dimension of fracture appearance and the compressive strength of CGFB: under the same seepage pressure, the higher the strength of CGFB with different angles, the greater the fractal dimension of fracture appearance; under the same crack angle, the greater the seepage pressure, the lower the strength and the larger the fracture fractal dimension. 3) Under the seepage-stress coupling, the fractal dimension of the failure fracture appearance has a good correlation with the dissipated energy, and the two increase linearly. This relative relationship is only related to the damage and fracture, and has nothing to do with the external conditions such as seepage pressure. The research results provide a theoretical basis for the stability analysis and instability prediction of artificial pillar containing joints, cracks and other geological defects under water-rich conditions in China.

Could the bulbar urethral end location on the cystourethrogram predict the outcome after posterior urethroplasty for pelvic fracture urethral injury?

ABSTRACT Objectives To identify cystourethrogram (CUG) findings that independently predict the outcome of posterior urethroplasty (PU) following pelvic fracture urethral injury (PFUI). Methods Findings of CUG included the location of the proximal end of the bulbar urethra in zones A (superficial) or B (deep) according to its relationship with the pubic arch. Others included the presence of pelvic arch fracture, bladder neck, and posterior urethral appearance. The primary outcome was the need for reintervention either endoscopically or by redo urethroplasty. Independent predictors were modeled using a logistic regression model and a nomogram was constructed and internally validated using 100-bootstrap resampling. Time-to-event analysis was performed to validate the results. Results A total of 196 procedures in 158 patients were analyzed. The success rate was 83.7% with 32 (16.3%) procedures requiring direct vision internal urethrotomy, urethroplasty, or both in 13 (6.6%), 12 (6.1%), and 7 (3.6%) patients, respectively. On multivariate analysis, bulbar urethral end located at zone B (odds ratio [OR]: 3.1; 95% confidence interval [CI]: 1.1–8.5; p = 0.02), pubic arch fracture (OR: 3.9; 95%CI: 1.5–9.7; p = 0.003), and previous urethroplasty (OR: 4.2; 95% CI: 1.8–10.1; p = 0.001) were independent predictors. The same predictors were significant in the time-to-event analysis. The nomogram discrimination was 77.3% and 75% in the current data and after validation. Conclusions The location of the proximal end of the bulbar urethra and redo urethroplasty could predict the need for reintervention after PU for PFUI. The nomogram could be used preoperatively for patient counseling and procedure planning.

Delay Time (δt) and Polarization Direction (φ) Analysis Based on Shear Wave Splitting (SWS) Method

The information of dominant polarization direction and the mapping of fracture intensity are among the most important informations during the monitoring of geothermal field reservoir evaluation, as an effort to develop geothermal energy production. The appearance of geothermal reservoir fractures caused by fluid injection and the production activity resulting in the decreased pore pressure and appearance of open weak zone. The micro-earthquake activity around the area can represent these fractures that appear in the geothermal reservoir. Shear Wave Splitting (SWS) analysis can be done based on the polarization of S wave through the anisotropy medium recorded by seismograph. There are two parameters related to Shear Wave Splitting: the polarization direction (φ) related to the micro fracture direction with its delay time (δt), showing the fractures density and its permeability area. The result of Shear Wave Splitting Analysis of the field X geothermal shows that two dominant polarization directions are NW-SE and NE-SW. It is caused by the fractures around the X field geothermal with similar fractures direction, and it is compatible with the distribution micro-earthquake hypocenter of the previous study. Based on the map of fractures intensity, the value range shows a relatively dense intensity value around 6.6 – 8.0 ms/km. The high value of intensity fractures indicates a high value of anisotropy around the area, and it is also confirming the presumption of the high permeability potential of the X geothermal field.

Investigation of Strain Fatigue Behavior for Inconel 625 with Laser Shock Peening.

With excellent creep resistance, high-temperature thermal strength and high-temperature fatigue strength, Inconel 625 is widely applied to fabricate structural components in the aerospace field, where fatigue life is a key point. Laser shock peening (LSP) is considered to improve the fatigue strength and fatigue crack growth resistance of metal materials. The present work was conducted to investigate the influence of LSP on strain-controlled fatigue behavior of Inconel 625. The surface microstructures of specimens before and after LSP were observed by transmission electron microscope (TEM). The strain-controlled fatigue loading tests with different strain amplitudes ranging from 0.4% to 1.2% were carried out on the specimens, and the topography of fracture appearance was examined by scanning electron microscope (SEM). The investigations showed that the specimens with LSP presented fewer crack initiations, shorter fatigue striations space and smaller dimples or micropores, which account for the enhancement of the fatigue life for the LSP specimens. Furthermore, the plastic deformation, ultra-fine grains, twins and dislocations caused by LSP could prevent crack initiation, crack propagation and ultimate fracture, hence prolonging the fatigue life of the Inconel 625. In addition, it was revealed that the cyclic strain hardening as well as cyclic strain softening remains almost the same to Inconel 625 with or without LSP.

Effect of carbon fiber preform structures on the mechanical properties of Cf@PyC/SiC composites

Cf@PyC/SiC composites, using needle-punched preforms, 3D orthogonal woven preforms and 3D 4-step braided preforms (braiding angles of 10°, 20° and 30°) as the reinforcement, were obtained through chemical vapor infiltration (CVI) method. The tensile strength before and after oxidation of the composites were investigated, and the microstructure, appearance of fracture and phase component of the composites were also analyzed. The results show that the mechanical properties and oxidation resistance of composites are greatly affected by the preform structures. The tensile strengths of 3D 4-step braided composites with the braiding angle of 10° are the best among all composites before and after oxidation, which are 266.40 ± 16.98 MPa and 238.66 ± 14.98 MPa. Before oxidation, the fibers and matrix at the fracture of 3D 4-step braided composites are in staggered distribution. The mechanical enhancement mechanisms of composites such as crack deflection, interface debonding and fiber pull-out, were beneficial to good performance and excellent mechanical properties. After oxidation, the deflection and branching effects of the interface on the crack are not fully manifested, and enhancement and toughening mechanisms are not fully played due to the oxidation of the carbon fiber and the PyC interface.

Evaluation of fatigue and creep-fatigue damage levels on the basis of engineering damage mechanics approach

Progressive degradation of material mechanical properties in the low cycle fatigue (LCF) and creep-fatigue (CF) interaction at high temperature affects the safe operation of in-service materials. By considering material degradation, the present work aims to establish a method for evaluating LCF and CF damage levels with wide applicability. Material-level data accumulations as well as theoretical foundations of LCF and CF are presented, including interrupted LCF and CF tests, subsequent tensile tests and energy-based damage models. A damage variable representing the degradation of material mechanical properties is then defined based on the tensile plastic strain energy density (TPSED), the physical mechanism of which is reflected in the microstructure evolution and fracture appearance. By taking into consideration the material degradation threshold in the traditional damage summation rule, a new three-dimensional (3D) damage interaction diagram is established, where the additional third axis indicates the material degradation level. Finally, taking GH4169 alloy and P92 steel as examples, this work demonstrates the implemented procedures of damage level evaluation, which has been validated via the experimental data.