Mechanical Properties and Corrosion Behaviour of 316l Stainless Steel Honeycomb Cellular Cores Manufactured by Selective Laser Melting

Selective laser technology is an additive technology that can allow for the manufacture of cellular structures using different types of metallic powder with complex applications in industries such as aerospace, automotive and medical implant industries. This paper presents the effect of climate and mechanical stresses on some honeycomb cellular cores, used in sandwich structures made of 316L stainless steel powder by applying the selective laser melting technology. The honeycomb cellular cores have undergone the microhardness testing and the resulting variation obtained from the analyzed samples was 225 ± 15 (HV_{0.3}). The compressive strength and the modulus of elasticity of the cellular structures were determined for flatwise and edgewise compressive stresses. Also, the cellular structures were subjected to accelerated corrosion tests in order to determine their mean life in application use conditions similar to those near seas and oceans. Also, a microstructural evaluation of salt deposits was carried out on the cellular structures subjected to accelerated corrosion tests using a salt spray test chamber

Simulation and Aerodynamic Analysis of the Flow Around the Sailplane Using CFD Techniques

In this paper, it was described the analysis and simulation process using the CFD technique and the phenomena that shows up in the engineering aero-spatial practice, directing the studies of simulation for the air flows around sailplane. The analysis and aerodynamic simulations using Computational Fluid Dynamics techniques (CFD) are well set as instruments in the development process of an aeronautical product. The simulation techniques of fluid flow helps engineers to understand the physical phenomena that take place in the product design since its prototype faze and in the same time allows for the optimization of aeronautical products’ performance concerning certain design criteria

Metodologia prognozowania trwałości zmęczeniowej oraz jej walidacja w oparciu o przyspieszone badania niezawodności dźwigni skoku wirnika nośnego

Because the industrial products have lifetimes, without failing, of up to millions of cycles, it is mandatory that the aerospace field puts into practice the accelerated testing techniques. The lifetime prediction methodology for industrial products presented in this paper was put into practice by performing accelerated reliability testing on an aerospace product (the pitch link of a helicopter). The results showed a significant reduction of the testing time and costs. One important aspect highlighted in this paper is the equivalence between accelerated reliability testing and the traditional reliability testing, by using the two fundamental principles of the accelerated experiments: first, the stresses applied must not alter the physical mechanism through which the defects are produced and second, the conservation of the distribution laws of the failure times. In this way, by equivalence of the accelerated experiments, the methodology contained in this paper was validated.Ponieważ okresy bezawaryjnego użytkowania produktów przemysłowych stosowanych w w branży lotniczej mogą wynosić nawet kilka milionów cykli, badanie niezawodności tych wyrobów wymaga zastosowania technik badania przyspieszonego. Metodologię prognozowania czasu pracy produktów przemysłowych przedstawioną w niniejszym artykule wykorzystano w badaniach przyspieszonych niezawodności dźwigni skoku wirnika nośnego helikoptera. Wyniki wykazały, że proponowana metoda pozwala na znaczną redukcję czasu i kosztów badania. Ważnym aspektem, podkreślonym w niniejszej pracy, jest równoważność przyspieszonych i tradycyjnych badań niezawodności, którą można uzyskać respektując dwie podstawowe zasady eksperymentów przyspieszonych: po pierwsze, zastosowane naprężenia nie mogą zmieniać fizycznego mechanizmu, który prowadzi do powstania wady, a po drugie, należy przestrzegać praw dotyczących rozkładu czasów uszkodzeń. Przeprowadzone badania potwierdzają poprawność proponowanej metody

Management of accelerated reliability testing

Pojam upravljanja nalazi se u svakoj aktivnosti iz programa ubrzanog ispitivanja pouzdanosti za industrijske proizvode, počevši od planiranja, realizacije i statističke obrade podataka. Ubrzano ispitivanje pouzdanosti (Accelerated Reliability Testing - ART) je eksperiment u kojemu: fizika mehanizma degradacije slična je mehanizmu u stvarnom radu uz primjenu danih kriterija; mjerenje pouzdanosti u velikoj je korelaciji s takvim mjerenjima u stvarnom radu uz primjenu danih kriterija. ART je degradacija industrijskih proizvoda zbog starenja koja dovodi do normalnog kvara kod rada na razinama naprezanja mnogo višim nego što bi se pri normalnoj uporabi moglo očekivati. Uzimajući u obzir aspekte u odnosu na statističku obradu eksperimentalnih podataka, odredili smo glavne parametre pouzdanosti, koji zatim određuju glavne karakteristike u odnosu na performansu i vrijeme proizvoda pod garancijom.The concept of management is found in every activity from the program of accelerated reliability tests for industrial products, starting from the planning, the realization and the statistical processing of the results. Accelerated Reliability Testing (ART) is an experiment in which: the physics of degradation mechanism is similar to the mechanism in the real operation using given criteria; the measurement of reliability has a high correlation with these respective measurements in the real operation using given criteria. An ART is an aging degradation of industrial products to produce normal failure by operating at stress levels much higher than would be expected in normal use. Taking into account the aspects regarding the statistical processing of experimental data, we determined the main reliability parameters, which in turn determine the main characteristics regarding the performance and the warranty period of the product

Design and Manufacturing Process for a Ballistic Missile

Designing a ballistic missile flight depends on the mission and the stress to which the missile is subject. Missile’s requests are determined by: the organization of components; flight regime type, engine configuration and aerodynamic performance of the rocket flight. In this paper has been developed a ballistic missile with a smooth fuselage type, 10 control surfaces, 8 directional surfaces for cornering execution, 2 for maneuvers of execution to change the angle of incidence and 4 stabilizers direction. Through the technology of gluing and clamping of the shell and the use of titanium components, mass of ballistic missile presented a significant decrease in weight and a structure with high strength

Statistical inferences for bearings life using sudden death test

In this paper we propose a calculus method for reliability indicators estimation and a complete statistical inferences for three parameters Weibull distribution of bearings life. Using experimental values regarding the durability of bearings tested on stands by the sudden death tests involves a series of particularities of the estimation using maximum likelihood method and statistical inference accomplishment. The paper detailing these features and also provides an example calculation

OPTIMUM DESIGN OF EXPERIMENTS FOR ACCELERATED RELIABILITY TESTING

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 reliability test

Reliability and Lifetime Assessment of Glider Wing’s Composite Spar through Accelerated Fatigue Life Testing

The evaluation of the reliability and the lifetime of aerospace components has become an important segment of the design stage. The aeronautical components are subjected to complex, rigorous tests and have a long test life. The main goal in the field of aviation is to have components with high reliability and quality and to meet the mandatory requirements and regulations. The spars are stiffening components positioned along the wing and which take up most of the load and are tested for fatigue over a long period of time. The spar which was analysed in this study has a sandwich structure with GFRP (glass fiber reinforced plastic) skin and foam core. In this paper, the performances in the static and dynamic conditions of the GFRP-foam sandwich structures cut out of the composite spar of a glider were analysed. Additionally, using accelerated techniques based on the three-point fatigue bending test, the main reliability indicators of the GFRP-foam sandwich structures were determined. Using the statistical processing of the experimental data and the Inverse Power Law–Weibull acceleration model, the mean number of cycles to failure, in normal testing conditions of the GFRP-foam specimens was determined, with a value of 102,814. Using the accelerated testing techniques of the GFRP-foam sandwich structures an important decrease of the test time (8.43 times) was obtained

Mechanical Performances of Lightweight Sandwich Structures Produced by Material Extrusion-Based Additive Manufacturing

Material Extrusion-Based Additive Manufacturing Process (ME-AMP) via Fused Filament Fabrication (FFF) offers a higher geometric flexibility than conventional technologies to fabricate thermoplastic lightweight sandwich structures. This study used polylactic acid/polyhydroxyalkanoate (PLA/PHA) biodegradable material and a 3D printer to manufacture lightweight sandwich structures with honeycomb, diamond-celled and corrugated core shapes as a single part. In this paper, compression, three-point bending and tensile tests were performed to evaluate the performance of lightweight sandwich structures with different core topologies. In addition, the main failure modes of the sandwich structures subjected to mechanical tests were evaluated. The main failure modes that were observed from mechanical tests of the sandwich structure were the following: face yielding, face wrinkling, core/skin debonding. Elasto-plastic finite element analysis allowed predicting the global behavior of the structure and stressing distribution in the elements of lightweight sandwich structures. The comparison between the results of bending experiments and finite element analyses indicated acceptable similarity in terms of failure behavior and force reactions. Finally, the three honeycomb, diamond-celled and corrugated core typologies were used in the leading edge of the wing and were impact tested and the results created favorable premises for using such structures on aircraft models and helicopter blade structures

Microstructure and micro-hardness analyses of titanium alloy Ti-6Al-4V parts manufactured by selective laser melting

Selective Laser Melting (SLM) is one of the powder based additive manufacturing technologies and it is, as well, the most rapidly growing technique in Rapid Prototyping. In this paper is presented a microstructure analysis using Scanning Electron Microscope (LEO 1525 SEM), of Ti6Al4V parts exposed into a corrosion environment. The corrosion environment was generated using a salt chamber with 5% and 10% NaCl concentration and an ACS-Sunrise climatic chamber. The parts were also subjected to tests in order to determine their micro-hardness, followed by a statistical processing of the obtained data. The parts, having a lattice structure, were built on a Selective Laser Melting machine