Search

Field load testing of bridges is often used as a reliable method for evaluating bridge performance. One of the downsides of field testing is that it usually requires a heavy instrumentation setup. This paper investigates the efficacy of using an artificial neural network (ANN) to predict a concrete slab bridge response and potentially reduce the number of instruments needed for field testing. The diagnostic test results from a single-span bridge are incorporated as the input dataset. Test truck location from the edge of the bridge, loading on the truck axles, and distance covered along the bridge by each axle are set as the input parameters, while the measured strains from 13 strain gauges are set as the target output. The neural network is then trained, tested, and validated, showing a good correlation with an acceptable average error percentage. Parametric studies are conducted next using the developed neural network to examine the influence of the number of strain gauges on the results. The network involving only three strain gauges with peak response shows a nearly similar correlation as the network with all 13 strain gauges. The developed neural networks are then used to predict the bridge response compared with the same bridge's proof load test results. The networks are found to predict the bridge response with high accuracy within a range of − 13.7 to + 18.6%, even with the reduced number of sensors. The results from this study demonstrate the potential of using ANNs to predict the bridge response and to optimize the sensor plans for on-site bridge load testing. [ABSTRACT FROM AUTHOR]

Ceramics exhibit stochastic fracture behavior due to internal and surface defects, thereby limiting their practical use. To address this issue, a combined method of 'self-crack-healing' and 'proof testing' has been proposed. However, to efficiently implement the method, a numerical analysis is required for preliminary investigation. This study establishes a finite element analysis methodology that enables the prediction of both strength recovery due to crack healing and the scatter of strength due to microstructural features. We determine the dependence of the scatter of the three-point bending strength on the healing conditions using the Weibull distribution and demonstrate the applicability of the proposed analysis method to proof tests. Results revealed that the proposed methodology can estimate the healing conditions and proof stresses by obtaining the microstructural information and oxidation kinetics parameters of the ceramic components in advance. • A method for predicting the strength recovery and scatter in ceramics was developed. • Finite element analysis was used coupling "crack healing" and "proof testing". • Fracture from internal defects becomes dominant as surface cracks heal. • The number of high-stress-enduring specimens increased with the healing time. • Virtual experiment verified the method feasibility and ceramics structural reliability. [ABSTRACT FROM AUTHOR]

In order to ensure the service life of the curved display panel, it is necessary to test and analyze the fatigue fragment life distribution of the curved display panel to predict the fragment rate of the product, and design the proof test scheme and life reliability test scheme. First of all, this paper has carried out Weibull test by 300pcs OC (open cell) samples of 27‐inch R1000 curved product. The Weibull life distribution parameters of the samples were obtained by fitting the test data (shape parameter k=0.337, size parameter λ= 1.86×108). Then, according to the requirement of customer (8000ppm fragment rate in 3 years), the proof test stress (σp=81.2 MPa) was calculated, and the life distribution model after proof test and zero failure reliability algorithm were derived. Finally, based on 90% confidence level (1‐α), life reliability test time (TL) and the number of samples (N), calculated the life reli ability test stress (σL=62.7 MPa) by reliability algorithm and life acceleration formula, determined the test scheme {TL, N, σL} and successfully passed the test verification. The static fatigue fragment life analysis method in this paper can accurately evaluate the fragments of curved display panel, guide the design and development of curved products, and effectively improve the reliability of curved display. [ABSTRACT FROM AUTHOR]

Ceramic dental prostheses exhibit increasing failure rates with service time. In particular, veneered crowns and bridges are susceptible to chipping and other fracture modes of failure. The purpose of this manuscript is to introduce a computational methodology and associated software that can predict the time-dependent probability of failure for ceramic prostheses and subsequently design proof test protocols to significantly enhance their reliabilities and lifetimes. Transient reliability and corresponding proof testing theories are introduced. These theories are coded in the Ceramic Analysis and Reliability Evaluation of Structures (CARES/Life) code. This software will be used to demonstrate the predictive capability of the theory as well as its use in designing proof test protocols to significantly improve the reliability (survival probability) and lifetime for dental prostheses. A three-unit fixed dental prosthesis (FDP) with zirconia core (ZirCAD) and veneering ceramic (ZirPress) are used to compare the predicted probabilities of failure to general clinical results. In addition, the capability to use proof testing to significantly improve the performance (reliability and lifetime) for this restoration is demonstrated. The probability of failure, P f , after five years without proof testing is predicted to be 0.337. This compares to clinical studies showing the failure rate to be between 0.2 and 0.23 after 5 years. After 10 years, reference 18 found the clinical failure rate for similar bridges (but not the same) to be up to 0.28 compared to the predicted P f of 0.38. The difference may be due to the analysis applying the load at an inclination of 75° which is more critical than vertical loading. In addition, clinical studies often report a simple survival rate instead of using Kaplan-Meier analysis to properly account for late enrollees. Therefore, true clinical failure rates may be higher than reported and may more closely match the predictions of this manuscript. The effectiveness of proof testing increases with selecting materials less susceptible to slow crack growth (higher SCG exponent, N). For example, proof testing the ZirPress glass-veneered bridges with N = 43.4 analyzed in this manuscript at 400 N bite force for 1 s which induces a failure rate during proof testing of 0.31, reduces the P f of bridges not proof tested from 0.45 to an attenuated-proof-tested probability of failure P fa of 0.21 after 20 years of usage. If another material is selected with improved resistance to SCG of N = 60 and the same loading conditions, the failure rate for the proof tested bridges after 20 years of service drops to 2 in 10,000 from 2.4 in 100 had they been not proof tested. The failure rate during proof testing for this material would be 5.1 in 100. Proof testing a material with absolutely no susceptibility to SCG at the same service load (in this case 285 N, not even the 400 N load used above) results in 0 % failure rate and is of course independent of time. The transient reliability and proof test theory presented in this paper and associated computational software CARES/Life were successful in predicting the performance of ceramic dental restorations when compared to clinical data. Well-designed proof test protocols combined with proper material selection can significantly enhance the reliabilities and lifetimes of ceramic prostheses. This proof test capability can be a translational technology if properly applied to dental restorations. [ABSTRACT FROM AUTHOR]

Stress rupture is a time-dependent failure mode occurring in unidirectional fiber composites under sustained tensile loads, resulting in highly variable lifetimes. Stress-rupture is of particular concern in composite overwrapped pressure vessels (COPVs) since it is unpredictable, and has catastrophic consequences. At the micromechanical level, stress rupture begins with the breakdown of individual fibers at random flaws, followed by local load-transfer to intact neighbors through shear stress in the matrix. Over time, the matrix creeps in shear causing lengthening overload zones around fiber breaks, resulting in even more fiber breaks, and eventually, formation of a catastrophically unstable break cluster. Current reliability models are direct extensions of classic stochastic breakdown models for a single fiber, and do not reflect such micromechanical activity. These models are adequate for modeling composite stress rupture under a constant load, however, they may be unrealistic under more complex loading profiles, such as a constant load that follows a brief 'proof test' at a load level up to 1.5 times this constant load. For carbon fiber/epoxy COPVs, current models predict a reliability, conditioned on survival of a proof test, that is always higher than the reliability without such a proof test. Concern exists that this is incorrect, and that a proof test may result in reduced reliability over time. While the failure probability during a proof test may be very low, overwrap damage occurs nonetheless in the form of a large number of fibers breaks that would not occur otherwise based on fiber Weibull strength statistics. This phenomenon of increased fiber breakage during a proof test is captured in the model we develop and that specifically builds on the micromechanical failure process described above. For typical proof-test load ratios, the model predicts conditional reliabilities for lifetime that are typically much lower than those calculated in the absence of a proof test. [ABSTRACT FROM AUTHOR]

The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness) become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces), as in bridges. The analyzed cases show that the shell’s span, geometry (static scheme) and the height of earth fill influence the stiffness of the structure. The soil-steel structure’s characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.

Fibre reinforced polymer composites have become an integral part of the bridge industry because of their versatility, high strength-to-weight ratio and enhanced durability. The novel idea of an all-composite structural system for road bridges has been proposed for the first time in Poland. The FRP bridge is a simply supported structure with 10.0 m long span and 7.66 m wide deck. The superstructure consists of four U-shaped girders bonded with sandwich deck slab, fabricated by means of a vacuum infusion. The bridge configuration, a finite element model developed for design and the proof test results are described in this paper. The test has shown that an all-composite bridge can meet the relevant strength and deflection design criteria. To develop an understanding of the long-term performance of the FRP bridge, a monitoring scheme utilizing distributed fibre-optic sensors was implemented to assess any changes in the bridge structural behaviour. [ABSTRACT FROM AUTHOR]

Purpose: to reveal distinctions in some psychophysiological characteristics of students with various level of motion activity. Materials and methods: the research was conducted on the basis of Kharkov national medical university. 312 students are investigated. Methods were used: questioning and pedagogical supervision. Results: the reliable distinctions are observed in the speed of processing of visual information at proof test at young men, and also in the subjective estimation by students of their health, activity and general self-appraisal in the analysis of psychophysiological indicators at students with the various level of motion activity. Conclusions: the reliable connection of the level of motion activity with a self-appraisal by students of their functional state is established.

Ceramic components will be used for electrical insulation and optical transparency on the heating and diagnostic systems of fusion reactors. As these form the boundary for the radioactive confinement, a defined procedure is required to demonstrate structural integrity. The established design codes are incompatible with ceramic materials for various reasons, predominantly the brittle nature of ceramics. CCFE and others have started to develop an in-house design code for the use of brittle materials in pressure vessels, this paper discusses the rationale behind the rules. The difficulty of reconciling the statistical nature of failure in ceramics with the deterministic nature in codes is addressed and it is suggested that the only way to achieve this is by a proof testing approach. The inherent weakness of the proof testing methodology, quantifying the strength loss during the qualification test is discussed. Further work is required to determine the validity of the rules experimentally. [ABSTRACT FROM AUTHOR]

Influence of physical training on intellectual working capacity and psychoemotional stability of students depending on specificity of the future professional work by means of proof test of Anfimova is considered. Students of the Kremenchug national university who were engaged have taken part in research. Positive influence of employment on physical training on intellectual working capacity is established. It is recommended to consider and plan physical training of students, as an obligatory component of the general teaching and educational process for increase of level of mastering of general-theoretical and special subjects.

Some dangerous failures of safety-instrumented systems (SISs) are detected almost immediately by diagnostic self-testing as dangerous detected (DD) failures, whereas other dangerous failures can only be detected by proof-testing, and are therefore called dangerous undetected (DU) failures. Some items may have a DU- and a DD-failure at the same time. After the repair of a DD-failure is completed, the maintenance team has two options: to perform an insert proof test for DU-failure or not. If an insert proof test is performed, it is necessary to decide whether the next scheduled proof test should be postponed or performed at the scheduled time. This paper analyzes the effects of different testing strategies on the safety performance of a single channel of a SIS. The safety performance is analyzed by Petri nets and by approximation formulas and the results obtained by the two approaches are compared. It is shown that insert testing improves the safety performance of the channel, but the feasibility and cost of the strategy may be a hindrance to recommend insert testing. [ABSTRACT FROM AUTHOR]

This paper proposes a holistic approach to model the Safety Instrumented Systems (SIS). The model is based on Switching Markov Chain and integrates several parameters like Common Cause Failure, Imperfect Proof testing, partial proof testing, etc. The basic concepts of Switching Markov Chain applied to reliability analysis are introduced and a model to compute the unavailability for a case study is presented. The proposed Switching Markov Chain allows us to assess the effect of each parameter on the SIS performance. The proposed method ensures the relevance of the results. [ABSTRACT FROM AUTHOR]

The maintenance of Safety Instrumented System (SIS), involving the proof test procedure, is a very important phase of maintaining the functional safety of a plant all over the life time. The proof testing gives the possibility of revealing the undetected dangerous failure of a SIS. The safety standards give a draft guideline for this activity but this guideline is problematical in everyday practice because it assumes that the proof test is always perfect. However the proof test is not always perfect in practice. The imperfectness of proof testing can be especially important for valves and other mechanical parts of SIS which have great influence on the performance of safety functions in process industry. This paper suggests a new failure model which takes into account that a proof test can be imperfect not just because it does not cover every possible failure modes but because a proof tested equipment cannot be always considered "as new" as inspired by the standard. This new model gives more detailed information about the different failure modes of valves under operation, maintenance and proof testing; and it makes the SIL calculation more accurate by modeling the degradation failures. It will be showed that the new model also may have influence on the proof testing strategy. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a new development for modelling the time-dependent probability of failure on demand of parallel architectures, and illustrates its application to multi-objective optimization of proof testing policies for safety instrumented systems. The model is based on the mean test cycle, which includes the different evaluation intervals that a module goes periodically through its time in service: test, repair and time between tests. The model is aimed at evaluating explicitly the effects of different test frequencies and strategies (i.e. simultaneous, sequential and staggered). It includes quantification of both detected and undetected failures, and puts special emphasis on the quantification of the contribution of the common cause failure to the system probability of failure on demand as an additional component. Subsequently, the paper presents the multi-objective optimization of proof testing policies with genetic algorithms, using this model for quantification of average probability of failure on demand as one of the objectives. The other two objectives are the system spurious trip rate and lifecycle cost. This permits balancing of the most important aspects of safety system implementation. The approach addresses the requirements of the standard IEC 61508. The overall methodology is illustrated through a practical application case of a protective system against high temperature and pressure of a chemical reactor. [Copyright &y& Elsevier]

Two kinds of theory for non-destructive inspection of ceramics were reviewed, which were derived by the authors using flaw-size distribution. In the sufficient condition theory (Realistic NDI), we had discussed about the screening flaw-size and a screening region. In the necessary and sufficient condition theory (Ideal NDI), we found that the screening flaw-size should be changed depending on stress state and specimen configuration. It was proved that there is one-to-one correspondence between Ideal NDI and a proof test. Applications to machining damage problems and surface strengthening of ceramics were also presented. [ABSTRACT FROM AUTHOR]

Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (σFmin) was compared with the theoretical minimum strength (σG) from room temperature (R.T.) to 1373 K. It was concluded that σG showed good agreement with σFmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [ABSTRACT FROM AUTHOR]

Abstract: Cast aluminium gearbox housings for railway vehicles are complex shaped components undergoing stochastic stresses during service. Early failures of housings led to broad investigations in order to clarify the causes. By a methodology determining the highly stressed areas, the load spectrum for different operational conditions by service strain measurements, the component related material behaviour, fatigue-life calculations and laboratory proof tests, criteria for optimum design, material selection and quality control were worked out. The methodology enabled the design of new housings that would meet the required failureless operational service. [Copyright &y& Elsevier]

Recently, the authors developed Si3N4, Al2O3 and mullite ceramics with good self-crack-healing abilities. It was shown that the optimized crack-healing condition to get high temperature strength was: 1573 K, 1 h, in air, and the healed zone exhibited the same strength as the base material up to about 1573 K (Si3N4 and Al2O3) and 1473 K (mullite), respectively. Using this good crack-healing ability, a new methodology to guarantee the reliability of ceramic components [crack-healing + proof test] was proposed. It was shown that reliability could be guaranteed before service by this technique, using about 200 samples. However, if a crack initiated during service, reliability would be severely impaired. Therefore, if a material can heal a crack during service, and if the healed zone has enough strength at the temperature of healing, it would be very desirable for structural integrity. From the above points of view, a new methodology to guarantee the structural integrity of ceramic components using in situ crack-healing ability was proposed and the usefulness is discussed using the test results in terms of crack-healing behavior and proof test theory by the authors. [Copyright &y& Elsevier]

The aim of this article is to present the optimization of a proof test procedure of ceramic hip joint ball heads. The proof test rejects defective samples in the production line before being implanted into human body. Thereby on every ceramic ball head a static load is applied, which is somewhat higher than the maximum physiological load. The magnitude of the applied load should not damage the samples which are free of flaws in the high stress area. The configuration of the proof test influences the stress distribution in the ball head, which should be similar to the physiological case. To determine the stress distribution, a non-linear finite element (FE) analysis was performed and the results were validated by measurements. With an iterative approach based on FE calculations the proof test configuration was optimized in such a way that the stress distribution in the ball head is similar to the stress distribution in vivo. In this study all ball heads showed very high fatigue resistance after being proof tested and fulfilled the requirements of the FDA (Food and Drug Administration, USA) described in the Guidance Document for the Preparation of Premarket Notifications for Ceramic Ball Hip System. The probability of a fracture of an implanted ceramic ball head can be decreased by the presented optimized proof test procedure. Latter can thus improve the reliability of ceramic hip joint ball heads. The study was supported by the KTI (Commission for Technology and Innovation, Switzerland). [Copyright &y& Elsevier]

Objectives. Prosthetic posts made of zirconia ceramics are beneficial because of their esthetic advantages. The mechanical reliability of ceramic posts is limited because of the strength level and the large scatter in strength of ceramic materials. The hypothesis of this study is that the failure of ceramic posts in vivo, which occur on low-quality posts because of critical microscopic defects can be excluded using the so-called proof test technology.Methods. The theory of the proof test technology is explained in detail in this study. In the experimental part 22 ceramic posts were tested at different proof load levels using a stepwise rotating four-point bending proof test device.Results. The experimental failures deviated from the theoretical failure probabilities by 0.24–12.69%. The deviation would be further reduced in a serial proof test using batches with a greater quantity of posts. The test eliminated those posts, which contained microscopic defects above a critical size of clinical relevance.Significance. The technology can help to reduce clinical failures of non-vital abutment teeth with ceramic posts, which are caused by critical microscopic defects of the ceramic material as a result of the industrial manufacturing process. [Copyright &y& Elsevier]

Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected. To overcome this problem, there are three ways: (a) inspect carefully and repair the unacceptable flaws, (b) toughen the ceramics by fiber reinforcing, (c) heal the flaws and recover strength. At the moment, there is no technique to heal embedded flaws. Therefore, a new technique to guarantee the reliability of ceramics components is demanded and so we proposed new technique: (crack-healing+proof test). For this technique, the mechanical behaviour of the crack-healed zone is very important for the structural integrity. Bending strength and fatigue strength test results of the crack-healed zone at high temperature are described. Using a process zone size failure criterion, an equation for the temperature-dependence of proof stress ( σ P T ) is derived. The accuracy of the equation has been verified for monotonic loading tests up to 1300°C. [ABSTRACT FROM AUTHOR]