Papers by Cristin Olimpiu MORARIU
Buletinul Institutului Politehnic din Iaşi, Sep 1, 2022
Nowadays quality management and specific tools can represent a challenge in SMEs (small and mediu... more Nowadays quality management and specific tools can represent a challenge in SMEs (small and medium enterprises). To assure the expected quality of the products, SPC (statistical process control) combined with industry 4.0 specifics offer instantaneous responses and triggers for needed actions. Therefore, risk analyses are used as enablers for quality-oriented behaviour, and risk mitigation and identification, together with collected data, represent a comprehensive system that leads enterprises to achieve the expected performance level needed to remain competitive in the market. In addition, risk management and quality management cannot be treated without looking at the maintenance activities and policies which can have a considerable impact on those two. This paper provides a comprehensive literature review of the papers from the quality management sector and articles where risk management and maintenance are seen as facilitators for quality improvement with an impact on the performance level. The main contribution of each paper is listed in the table which simplifies the reader's access to the work done in the field and the overview presented enables easy access to trends in this field and offers a starting point for future research by presenting the gaps.
Bulletin of the Polytechnic Institute of Iași. Machine constructions Section
Nowadays quality management and specific tools can represent a challenge in SMEs (small and mediu... more Nowadays quality management and specific tools can represent a challenge in SMEs (small and medium enterprises). To assure the expected quality of the products, SPC (statistical process control) combined with industry 4.0 specifics offer instantaneous responses and triggers for needed actions. Therefore, risk analyses are used as enablers for quality-oriented behaviour, and risk mitigation and identification, together with collected data, represent a comprehensive system that leads enterprises to achieve the expected performance level needed to remain competitive in the market. In addition, risk management and quality management cannot be treated without looking at the maintenance activities and policies which can have a considerable impact on those two. This paper provides a comprehensive literature review of the papers from the quality management sector and articles where risk management and maintenance are seen as facilitators for quality improvement with an impact on the perform...
IOP Conference Series: Materials Science and Engineering, 2021
The paper depicts the method of statistical processing of experimental results, obtained by testi... more The paper depicts the method of statistical processing of experimental results, obtained by testing bearings on the test stands, using the maximum likelihood estimators and/or Best Linear Invariant Estimator. To verify statistical assumptions regarding parameters and reliability indicators of bearings, as well as, to determine confidence intervals, the article contains two original algorithms that allow obtaining values of some specific random variables by Monte Carlo numerical simulation. The statistical inferences are made through these values. The paper also, contains two case studies using data from failures and time truncated tests of bearings.
MATEC web of conferences, 2021
To cope with the pollution norms and an improvement of the combustion of the internal combustion ... more To cope with the pollution norms and an improvement of the combustion of the internal combustion engines, high-quality holes with diameters smaller than 145 µm are needed for the manufacture of fuel injection nozzles. The current practice of using drilling by electro-discharge machining of fuel injection nozzles is limited in terms of the size of the hole it can efficiently produce and the time required for drilling. In addition, the cost of the tool is high. This paper presents an investigation into a sequential laser and electro-discharge micro-drilling technique for the manufacture of fuel injection nozzles. A pilot hole drilled with a laser is removed by electrodischarge. It was found that this hybrid process eliminated the problems of reformed and heat-affected areas usually associated with the laser drilling process. The new process has allowed a reduction in total drilling time compared to standard electro-discharge machining drilling, as less material is removed from the electro-discharge machining. The quality of the holes is as good as direct electro-discharge machining drilling. This technique has allowed valuable cost savings and increased production capacity for the manufacture of the fuel injector nozzle.
European Journal of Materials Science and Engineering
In order to obtain automobiles that comply with the increasingly severe pollution standards, as w... more In order to obtain automobiles that comply with the increasingly severe pollution standards, as well as to obtain some of them at low costs, a technical-economic approach to the flow of the fuel fluid through the flow holes of the injection nozzles is necessary. Through the effect of hydropolishing the geometric characteristics of the hydraulic flow path, the flow path is modeled, reducing cavitation and achieving high performance. The fluid used is a fluid that has properties close to diesel and has SiC microparticles in suspension (manufacturing costs in in this case they are reduced). The article contains an analysis of the influence of the abrasive flow on the geometric parameters of the nozzle and implicitly on the operation of thermal engines. The results provide a means of identifying parameters that can be compared and evaluated in order to achieve the desired level of hydrodynamic efficiency.
The organizing and the execution out of the durability/reliability of the products represent comp... more The organizing and the execution out of the durability/reliability of the products represent complex activities from an organizational standpoint and are also big resources consumers. That is why in this paper we present a calculation method of the testing period of the reliability of products, by using the model of exponential distribution, which allows the estimation of the mean duration of a censored and/or complete test, as well as of the confidence intervals for this duration. The knowledge of these values allows the planning and the adequate allocation of the resources for the testing activities. Also, the accuracy of the obtained results, by using the proposed calculation methodology, was checked using the Monte Carlo simulation.
Fiabilitate şi Durabilitate, 2014
In this paper is presented a case study that demonstrates how design to experiments (DOE) informa... more In this paper is presented a case study that demonstrates how design to experiments (DOE) information can be used to design better accelerated reliability tests. In the case study described in this paper, will be done a comparison and optimization between main accelerated reliability test plans (3 Level Best Standard Plan, 3 Level Best Compromise Plan, 3 Level Best Equal Expected Number Failing Plan, 3 Level 4:2:1 Allocation Plan). Before starting an accelerated reliability test, it is advisable to have a plan that helps in accurately estimating reliability at operating conditions while minimizing test time and costs. A test plan should be used to decide on the appropriate stress levels that should be used (for each stress type) and the amount of the test units that need to be allocated to the different stress levels (for each combination of the different stress types' levels). For the case study it used ALTA 7 software what provides a complete analysis for data from accelerated...
In accelerated life testing, products are exposed to stress levels higher than those at normal us... more In accelerated life testing, products are exposed to stress levels higher than those at normal use in order to obtain information in a short time. In this paper ,we expand the limits of performing accelerated life tests to an aerospace product (supple platinum). Specimens from the IAR 330 Puma helicopter structure, made of supple platinum, were subjected to accelerated life testing, and a significant reduction of the testing time was obtained. A simulation of the accelerated life testing data from the same case study was performed using the Monte Carlo method, with the purpose of comparing the data resulting from the experimental study (accelerated life tests) with the simulated data.
Strojniški vestnik – Journal of Mechanical Engineering, 2019
MATEC Web of Conferences, 2017
Transactions of FAMENA, 2018
The paper presents an analysis of the reliability of front blade, rear blade and frame of the tow... more The paper presents an analysis of the reliability of front blade, rear blade and frame of the towed grader as well as experimental validation of the results obtained from the finite element analysis. The analyzed prototype was designed for maintenance and repair of forest roads and equipped with two types of blades for cleaning and levelling the ground surface. Lifetimes of towed grader attachments can be estimated with high accuracy using threeparameter Weibull distribution. The values of the location parameter γ were determined by using the maximum values of the correlation coefficient, while the method of maximum likelihood was used for the point estimation of the parameters. Because higher values of the shape parameter had been obtained, the point estimation and estimation with confidence intervals of components lifetimes were performed. The analysis of the results indicates that the used assumptions may not fully take the complex stresses encountered in use into account.
BioResources, 2017
Balsa wood is a natural cellular material with an excellent resistance-toweight ratio that is ide... more Balsa wood is a natural cellular material with an excellent resistance-toweight ratio that is ideal for manufacturing the core of sandwich structures. In this study, sandwich specimens with a carbon-fiberreinforced polymer (CFRP) skin and a balsa wood core were tested with static and dynamic loading. Three-point flexural tests in static regime determined the mechanical characteristics of the CFRP-balsa specimens that were needed for subsequent fatigue strength tests. Also, experimental research was performed on the Charpy impact response of the CFRP-balsa sandwich specimens. This study implemented an accelerated fatigue testing method to identify and predict the mean fatigue life of the CFRP-balsa sandwich specimens subjected to cyclic fatigue via three-point flexural tests. Using the accelerated fatigue and the three-point flexural testing methodology on the CFRP-balsa sandwich specimens, the testing period was reduced by 11.9 times, and thus the material costs necessary for the tests were also reduced. Also, the breaking surfaces were analysed to reveal the failure modes of CFRP-balsa specimens subjected to static and fatigue tests at threepoint flexural and at impact tests.
The use of bearings in very different domains, characterized by working conditions with high vari... more The use of bearings in very different domains, characterized by working conditions with high variety, implies that the failing modes of the bearings are various, also. The purpose of using reliability models and statistical models for the analysis of the experimental results, obtained by observing different types of failures and deterioration phenomena, is represented by evaluating the preliminary reliability of the products. As a consequence, the overall look at the lifespan of products has to allow for the global accounting of failing possibilities, through realist intertwining of the accidental causes for failing with the controlled, determined ones. The image has to be filled in with its static aspect. It is understood that the preliminary reliabilities calculated have to be considered as static values with resulting distributions, accounting for the fact that all the service conditions (cycle, precision, temperature, environment etc.), external loadings, dimensions and material...
This paper presents a study about indicators of reliability (reliability function, non-reliabilit... more This paper presents a study about indicators of reliability (reliability function, non-reliability function, failure rate, probability density function, mean life) of gears using Monte Carlo simulation based on the time of failure. The technical systems ́ increase of their automation and complexity degree and ask for in-depth research of their precision and reliability, as a warranty for increasing the level of quality and the competitiveness of those industrial products. The main advantages of the accelerated life tests reside in the decrease of the testing duration and of the allocated costs. As a result, the use of accelerated life tests represents a main and permanent concern of practitioners from the areas of mechanical products ́ reliability.
In reliability studies are many situations in which the point estimator is very difficult to obta... more In reliability studies are many situations in which the point estimator is very difficult to obtain and the exact interval estimates are practically impossible to calculate. In these cases where the form of is complicated, the calculus of interval estimates are based on the asymptotically properties of maximum likelihood method. In recent years a computer-intensive technique called the bootstrap estimate that was developed to be used for this kind of problems. The paper presents how to use these estimators in the case of exponential distribution. This type of statistical model was chosen because the point estimator and the interval estimates are determined very simple with accuracy.
In this paper, we present a calculation methodology of the testing duration of the products' ... more In this paper, we present a calculation methodology of the testing duration of the products' reliability, using the Weibull distribution, which allows the estimation of the mean duration of a censored and/or complete test, as well as of the confidence intervals for this duration. By using these values we can improve the adequate planning and allocation of material and human resources for the specific testing activities. The proposed methodology and the results' accuracy were verified using the Monte Carlo data simulation method.
MATEC Web of Conferences, 2021
To cope with the pollution norms and an improvement of the combustion of the internal combustion ... more To cope with the pollution norms and an improvement of the combustion of the internal combustion engines, high-quality holes with diameters smaller than 145 µm are needed for the manufacture of fuel injection nozzles. The current practice of using drilling by electro-discharge machining of fuel injection nozzles is limited in terms of the size of the hole it can efficiently produce and the time required for drilling. In addition, the cost of the tool is high. This paper presents an investigation into a sequential laser and electro-discharge micro-drilling technique for the manufacture of fuel injection nozzles. A pilot hole drilled with a laser is removed by electrodischarge. It was found that this hybrid process eliminated the problems of reformed and heat-affected areas usually associated with the laser drilling process. The new process has allowed a reduction in total drilling time compared to standard electro-discharge machining drilling, as less material is removed from the ele...
Materiale Plastice, Apr 17, 2020
The research carried out within this paper addresses the issue of impact analysis with a spherica... more The research carried out within this paper addresses the issue of impact analysis with a spherical ball of an automobile fender, following two directions: the finite element method modeling of named part and situation, and experimental validation of the study mentioned beforehand. The part itselfcar fenderis represented by a thermoset composite panel armed with Kevlar-Carbon fibers, while the analyzed situation is depicted as a Charpy/Izod test with a spherical ball on the specified component. The evaluation of named inquiry is performed in a virtual environment by means of FEA and verified accordingly within laboratory testing.
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Papers by Cristin Olimpiu MORARIU