Relationship between diameter of split Hopkinson pressure bar and minimum loading rate under rock failure

In order to investigate the relationship between bar diameter and loading rate of the split Hopkinson pressure bar(SHPB) setup under the failure of rock specimen and realize the medium strain rate loading of specimen,new SHPB setups with different elastic bar's diameters of 22,36,50 and 75 mm were constructed.The tests were carried out on these setups at different loading rates,and the specimens had the same diameter of elastic bars and same ratio of length to diameter.The test results show that the larger the elastic bar's diameter is,the less the loading rate is needed to cause specimen failure,they show good power relationship,and that under the same strain rate loading,specimens are broken more seriously with larger diameter SHPB setup than with smaller one.

Dynamic tensile strength and failure mechanisms of thermally treated sandstone under dry and water-saturated conditions

To study the tensile strength and failure mechanisms of rock with hydro-thermal coupling damage under different loading rates,a series of static and dynamic splitting tests were conducted on thermally treated sandstone under dry and water-saturated conditions.Experimental results showed that high temperatures effectively weakened the tensile strength of sandstone specimens,and the P-wave velocity declined with increasing temperature.Overall,thermal damage of rock increased gradually with increasing temperature,but obvious negative damage appeared at the temperature of 100℃.The water-saturated sandstone specimens had lower indirect tensile strength than the dry ones,which indicated that water-rock interaction led to secondary damage in heat-treated rock.Under both dry and water-saturated conditions,the dynamic tensile strength of sandstone increased with the increase of strain rate.The water-saturated rock specimens showed stronger rate dependence than the dry ones,but the loading rate sensitivity of thermally treated rock decreased with increasing treatment temperature.With the help of scanning electron microscopy technology,the thermal fractures of rock,caused by extreme temperature,were analyzed.Hydro-physical mechanisms of sandstone under different loading rate conditions after heat treatment were further discussed.

Dynamic compressive property and failure behavior of extruded Mg-Gd-Y alloy under high temperatures and high strain rates

For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.

RELIABILITY ANALYSIS FOR A REPAIRABLE PARALLEL SYSTEM WITH TIME-VARYING FAILURE RATES

To solve a real problem:how to calculate the reliability of a system with time-varying failure rates in industry systems,this paper studies a model for the load-sharing parallel system with time-varying failure rates,and obtains calculating formulas of reliability and availability of the system by solving differential equations.In this paper,the failure rates are expressed in polynomial configuration.The constant,linear and Weibull failure rate are in their special form.The polynomial failure rates provide flexibility in modeling the practical time-varying failure rates.

Rotational failure analysis of spherical-cylindrical shell pressure controllers related to gas hydrate drilling investigations

In situ pressure-preserved coring(IPP-Coring)technology is considered one of the most efficient methods for assessing resources.However,seal failure caused by the rotation of pressure controllers greatly affects the success of pressure coring.In this paper,a novel spherical-cylindrical shell pressure controller was proposed.The finite element analysis model was used to analyze the stress distribution and deformation characteristics of the pressure controller at different rotation angles.The seal failure mechanism caused by the rotation of the pressure controller was discussed.The stress deviation rate was defined to quantitatively characterize the stress concentration.Based on the test equipment designed in this laboratory,the ultimate bearing strength of the pressure controller was tested.The results show that the rotation of the valve cover causes an increase in the deformation on its lower side.Furthermore,the specific sealing pressure in the weak zone is greatly reduced by a statistically significant amount,resulting in seal failure.When the valve cover rotates 5°around the major axis,the stress deviation rate is-92.6%.To prevent rotating failure of the pressure controller,it is necessary to control the rotation angle of the valve cover within 1°around the major axis.The results of this research can help engineers reduce failure-related accidents,provide countermeasures for pressure coring,and contribute to the exploration and evaluation of deep oil and gas resources.

Application of the Bayes’ theory to the failure rate evaluation of electrical apparatus

The Weibull distribution has been widely used in reliability fields. A mixed Weibull distribution represents a popu- lation that consists of several Weibull subpopulations. In this paper, a new approach which combines the least-squares method with Bayes’ theorem, takes advantage of the parameter estimation for single Weibull distribution is developed to estimate the pa- rameters of each subpopulation. The estimates given by this paper also satisfy the maximum likelihood equation. The estimates of the failure rate of the mixed Weibull population are given. An actual test data is computed by using the proposed method. The Kolmogorov-Smirnov goodness-of-fit test turns out that the proposed method yields more accurate result.

Why do thoracic epidurals fail?A literature review on thoracic epidural failure and catheter confirmation

Thoracic epidural anesthesia(TEA)has been the gold standard of perioperative analgesia in various abdominal and thoracic surgeries.However,misplaced or displaced catheters,along with other factors such as technical challenges,equipment failure,and anatomic variation,lead to a high incidence of unsatisfactory analgesia.This article aims to assess the different sources of TEA failure and strategies to validate the location of thoracic epidural catheters.A literature search of PubMed,Medline,Science Direct,and Google Scholar was done.The search results were limited to randomized controlled trials.Literature suggests techniques such as electrophysiological stimulation,epidural waveform monitoring,and x-ray epidurography for identifying thoracic epidural placement,but there is no one particular superior confirmation method;clinicians are advised to select techniques that are practical and suitable for their patients and practice environment to maximize success.

Allograft tissue irradiation and failure rate after anterior cruciate ligament reconstruction:A systematic review

AIM:To evaluate whether anterior cruciate ligament(ACL) allograft irradiation is effective for sterility without compromising graft integrity and increasing failure rate.METHODS:A literature search was conducted using Pub Med,Cochrane,and Google.The following search terms were used:"Gamma irradiation AND anterior cruciate ligament AND allograft" with a return of 30 items.Filters used included:English language,years 1990-2015.There were 6 hits that were not reviewed,as there were only abstracts available.Another 5 hits were discarded,as they did not pertain to the topic of interest.There were 9 more articles that were excluded:Three studies were performed on animals and 6 studies were meta-analyses.Therefore,a total of 10 articles were applicable to review.RESULTS:There is a delicate dosing crossover where gamma irradiation is both effective for sterility without catastrophically compromising the structural integrity of the graft.Of note,low dose irradiation is considered less than 2.0 Mrad,moderate dose is between 2.1-2.4 Mrad,and high dose is greater than or equal to 2.5 Mrad.Based upon the results of the literature search,the optimal threshold for sterilization was found to be sterilization at less than 2.2 Mrad of gamma irradiation with the important caveat of being performed at low temperatures.The graft selection process also must include thorough donor screening and testing as well as harvesting the tissue in a sterile fashion.Utilization of higher dose(≥ 2.5 Mrad) of irradiation causes greater allograft tissue laxity that results in greater graft failure rate clinically in patients after ACL reconstruction.CONCLUSION:Allograft ACL graft gamma irradiatedwith less than 2.2 Mrad appears to be a reasonable alternative to autograft for patients above 25 years of age.

Is heart rate reduction more important than target dose in chronic heart failure therapy with a beta-blocker?

1 Introduction Beta-adrenoceptor blocking agents(beta-blockers)are now well established as cornerstone therapy in patients with systolic chronic heart failure(CHF).[1]Clinical data have overwhelmingly proven the beneficial effects of beta-blocker therapy in terms of improving patient prognosis,decreasing requirements for hospitalization,and postponing disease progression.[2-4]However,it remains unclear what the optimal efficacious and safe dose for an individual patient with CHF is,and whether this can simply be inferred from the target dose for each beta-blocking agent as used in the major clinical trials.

Discharge heart rate and future events among Japanese patients with acute heart failure receiving beta-blocker therapy

Background: Randomized trials have demonstrated the efficacy of beta-blockers (BBs) in heart failure (HF) patients. We sought to assess the impact of BBs on long-term outcome;in particular, we assessed the association between outcome and BB dose and discharge heart rate. Methods and Results: Prescriptions for dispensed medication and outcomes were identified from a prospective, single-institution HF registry. Long-term prognosis was compared between users and non-users of BBs. BB users were further divided into 2 groups based on dose (full and non-full dose) and discharge heart rate (70 bpm was significantly associated with impaired long-term outcome (HR = 1.872, P = 0.04). Conclusions: Optimizing heart rate, rather than maximizing BB dose, appears to be an appropriate treatment strategy for the beta-sensitive Japanese population.

Effect of heating-rate on failure temperature of pre-loaded magnesium alloy

The response and failure of magnesium alloy AZ31 specimens subjected to different pre-loaded-stress levels and heating rates were investigated with a Gleeble-1500 thermo-mechanical material testing system.It is found that the increases of either pre-loaded stresses or heating-rates decrease the failure temperatures of the specimens.The metallographs of the tested specimens were also observed.It is shown that the high heating-rate may cause stronger local thermal inconsistency,which remarkably increases the microdefects and reduces the macroscopic mechanical properties of the material.

A very high frequency index of heart rate variability for evaluation of left ventricular systolic function and prognosis in chronic heart failure patients using five-minute electrocardiogram

Objective A novel index based on fi-equency-domain analysis of heart rate variability （HRV） was tested on patients with reduced left ventricular systolic function. This index, namely VHFI, was defined as the very high frequency （VHF） component of the power spectrum normalized to represent its relative value in proportion to the total power minus the very low frequency component. Methods Patients （n = 130） were divided into a study group, consisting 66 patients with decreased left ventricular systolic function, and a control group, consisting 64 patients with normal heart structure and function and without severe coronary artery stenosis （〈 50%）. Results VHFI in the study group was significantly higher than that in the control group （19.17 ± 13.35 vs 11.37 ± 10.77, P 〈 0.001）. Cardiac events occurred in 18 patients during follow-up （33.34 i 3.26 months）. Defining the positive test as VHFI =15 and negative test as VHFI 〈15, achieved a sensitivity of 57.58% and a specificity of78.13% for predicting decreased left ventricular systolic function, and achieved a sensitivity of 66.67% and a specificity of 64.29% for predicting cardiac events. Univariate Cox regression analysis showed that positive VHFI test was an independent variable in predictive cardiac events. Conclusions The results suggest that VHFI is a useful tool for quick evaluation of left ventricular systolic function and prediction of prognosis

Modeling the Failure Rate of a Standby Multi-Component System and Improving Reliability

Evaluating the reliability of a system requires knowledge of the failure modes to which it is subjected. Complex topology systems generally require a high level of availability, which is a function of the arrangement of elements (components) in the system. To avoid serious failures for such complex systems, recourse can be had to the redundancy techniques available in the literature. These techniques help to improve system reliability, without affecting the reliability of system components. This paper is interested in the proposal of a model for evaluating the failure rate of a standby multi-components system and in improving the reliability of mechanical systems, arranged in a topology (series, parallel, or mixed).

A Mathematical Methodology for the Preventive Study of the Failure Rate to Optimize the Maintenance Program of a Public Work: Economic-Management Aspects for Safety and Quality

In this paper we analyze the problem of the assessment of the failure rate of the complex public work system and the engineering part of it (bridge, tunnel, etc.), examining the case of serious maintenance problems, such as those which occurred in the recent disaster of the "Morandi bridge". The original mathematical methodology envisaged makes it possible to optimize the safety and quality scenarios of the operation and infrastructure in question, also from an economic-management point of view, evaluating every aspect in an integrated way and for the entire period life. The scientific results obtained are of particular interest for the study of maximization of the planning protocols of "terotechnological" interventions, providing a contribution to the science of programmed maintenance for the mobility networks and for more complex parts such as bridges and tunnels.

Failure rate,return-to-sports and magnetic resonance imaging after meniscal repair:119 patients with 7 years mean follow up

BACKGROUND One of the most important factors to consider in relation to meniscal repair is the high failure rate reported in the existing literature.AIM To evaluate failure rates,return to sports(RTS)rate,clinical outcomes and magnetic resonance image(MRI)evaluation after meniscus suture repair for longitudinal tears at a minimum 2-year-follow-up.METHODS We conducted a retrospective review of meniscal repairs between January 2004 and December 2018.All patients treated for longitudinal tears associated or not with an anterior cruciate ligament reconstruction(ACL-R)were included.Meniscal ramp lesions,radial and root tears,associated with multiligament injuries,tibial fracture and meniscal allograft transplants were excluded.Surgical details and failure rate,defined as symptomatic patients who underwent a revision surgery,were analyzed.As isolated bucket handle tears(BHTs)were usually associated with higher failure rates,we compared BHTs and not BHTs associated or not with an ACL-R.Since 2014,the inside-out technique using cannulas and suture needles with 2-0 Tycron began to predominate.In addition,the number of stitches per repair was increased.In view of differences in surgical technique,we compared two different cohorts:before and after 2014.We recorded the RTS according to the level achieved and the time to RTS.Lysholm and IKDC scores were recorded.Patients were studied with x-rays and MRI as standard postoperative control.RESULTS One hundred and nineteen patients were included with a mean follow up of 7 years(SD:4.08).Overall failure rate was 20.3%at a mean 20.1 mo.No statistically significant differences were found when comparing failure for medial and lateral meniscal repair(22.7%and 15.3%,P=0.36),BHTs and not BHTs(26%and 17.6%,P=0.27),isolated or associated with an ACL-R(22.9%and 18%,P=0.47),or when comparing only BHTs associated with an ACL-R(23%and 27.7%,P=0.9)or not.When comparing cohorts before and after 2014,we found a significant decrease in the overall failure rate from 26%to 11%(P<0.03).Isolated lesions presented a decrease from 28%to 6.6%(P=0.02),BHTs from 34%to 8%(P=0.09)and those associated with an ACL-R from 25%to 10%(P=0.09).Mean RTS time was 6.5 mo in isolated lesions and 8.64 mo when associated with an ACL-R.Overall,56%of patients returned to the same sport activity level.Mean pre and postoperative Lysholm scores were 64 and 85(P=0.02),and IKDC 58 and 70(P=0.03).Out of 84 asymptomatic patients evaluated with MRI,39%were classified as“not healed”and 61%as“healed”.CONCLUSION Even though the overall failure rate of our series was 20.3%,we found a statistically significant decrease from 26%to 11%,not only for isolated lesions,but also for BHT’s and those associated with an ACL-R when comparing our series in two different cohorts,most probably due to improvements in surgical technique.

Effects of Shenkang Injection Combined with Hemodialysis on Dialysis Rate and Nutriture in Patients with Chronic Renal Failure

OBJECTIVE: To explore the effects of Shenkang Injection combined with hemodialysis on dialysis rate and nutriture in patients with chronic renal failure (CRF).METHODS: A total of 110 CRF patients admitted in the hospital from January 2016 to January 2018 were randomly divided into 2 groups.The control group was treated with hemodialysis while the observation group was additionally treated with Shenkang Injection on the treatment basis of the control group.They were treated for 4 weeks and reexamined 1 d after the treatment.Renal function,nutriture,dialysis adequacy,oxidative stress level and inflammatory factor level in the 2 groups were determined before and after the treatment,and traditional Chinese medicine (TCM) syndrome score,dialysis rate within 1 week and incidence of adverse reactions during the treatment were counted before and after the treatment.RESULTS: After the treatment,the levels of serum creatinine (Scr) and urea nitrogen (BUN) in the observation group were lower than those in the control group,and the endogenous creatinine clearance rate (Ccr) was higher than that in the control group (P < 0.05).After the treatment,the nutriture in the observation group was better than that in the control group (P < 0.05).After the treatment,the dialysis rate and time average concentration of urea (TACurea) in the observation group were lower than those in the control group,while the overall urea clearance rate (Kt/V) and protein catabolic rate (PCR) were higher than those in the control group (P < 0.05).After the treatment,the TCM syndrome scores in the observation group was lower than that in the control group (P < 0.05) and the level of serum malondialdehyde (MDA) in the observation group was lower than that in the control,while the level of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in the observation group were higher than those in the control group (P < 0.05).After the treatment,the levels of inflammatory factors in the observation group were lower than those in the control group (P < 0.05).No serious adverse reactions occurred in the 2 groups.CONCLUSION: Shenkang Injection combined with hemodialysis for the treatment of CRF can effectively improve clinical symptoms and nutriture,and reduce the dialysis rate.

Effect of heating-rate on failure temperature of pre-loaded brass H62

The response and failure of brass H62 specimens subjected to different levels of pre-loaded stresses and heating rates were investigated using a Gleeble-1500 thermal-mechanical material testing system. The metallographs of the tested material were also observed and analyzed. It is found that the increase of either pre-loaded stress or heating-rate decreases the failure temperature. Metallographic analysis shows that high heating-rate may cause stronger local thermal inconsistency(LTI) and remarkably increase the microdefects in the material,which may markedly degrade the macroscopic mechanical properties of the material.

Research on large-scale cascading failure of power systems using synergistic effect

This paper discusses the primary causes from the point of synergistic effects to improve power system vulnerability in the power system planning and safety operation. Based on the vulnerability conception in the complex network theory the vulnerability of the power system can be evaluated by the minimum load loss rate when considering power supply ability.Consequently according to the synergistic effect theory the critical line of the power system is defined by its influence on failure set vulnerability in N-k contingencies.The cascading failure modes are proposed based on the criterion whether the acceptable load curtailment level is below a preset value.Significant conclusions are revealed by results of IEEE 39 case analysis weak points of power networks and heavy load condition are the main causes of large-scale cascading failures damaging synergistic effects can result in partial failure developed into large-scale cascading failures vulnerable lines of power systems can directly lead the partial failure to deteriorate into a large blackout while less vulnerable lines can cause a large-scale cascading failure.

Research on the energy evolution characteristics and the failure intensity of rocks

It is pretty challenging and difficult to quantitatively evaluate the intensity of dynamic disasters in deep mining engineering.Based on the uniaxial loading-unloading experiments for five types of rocks,this paper investigated the energy evolution characteristics,and identified the damage and crack propagation thresholds.Also,the fragment size distributions of the rocks after failure were analyzed.The energy release rate(Ge)and energy dissipation rate(Gd)were then proposed to describe the change of energies per unit volume and per unit strain.Results demonstrated that the more brittle rocks had the shorter stage of unstable crack growth and the lower induced damage at crack damage thresholds.The evolution characteristics of the strain energy rates can be easily identified by the crack propagation thresholds.The failure intensity index(FId),which equals to the values of Ge/Gd at the failure point,was further put forth.It can account for the brittleness of the rocks,the intensity of rock failure as well as the degree of rock fragmentation.It was revealed that a higher FId corresponded to a lower fractal dimension and stronger dynamic failure.

Mechanical behavior and failure mechanism of polyurea nanocomposites under quasi-static and dynamic compressive loading

Polyurea is an elastomeric material that can be applied to enhance the protection ability of structures under blast and impact loading.In order to study the compressive mechanical properties of SiC/polyurea nanocomposites under quasi-static and dynamic loading,a universal testing machine and split Hopkinson pressure bar(SHPB)apparatus were used respectively.The stress-strain curves were obtained on polyurea and its composites at strain rates of 0.001e8000 s1.The results of the experiment suggested that increase in the strain rates led to the rise of the flow stress,compressive strength,strain rate sensitivity and strain energy.This indicates that all of the presented materials were dependent on strain rate.Moreover,these mechanical characters were enhanced by incorporating a small amount of SiC into polyurea matrix.The relation between yield stress and strain rates were established using the power law functions.Finally,in order to investigate the fracture surfaces and inside information of failed specimens,scanning electron microscopy(SEM)and micro X-ray computed tomography(micro-CT)were used respectively.Multiple voids,crazes,micro-cracks and cracking were observed in fracture surfaces.On the other hand,the cracking propagation was found in the micro-CT slice images.It is essential to understand the deformation and failure mechanisms in all the polyurea materials.