Determination of Characteristics of a Laminated Torsion Bar Spring by Using Correction Coefficients in Respect to Clamping Conditions

The laminated torsion bar is used for many mechanical purposes where a large angle with decreasing or increasing torque is necessary. The design of laminated torsion bar relates to dissipation of energy by friction between laminae, number of laminae and clamp conditions at the end of bar. The paper presents theoretical, experimental and numerical analysis of a laminated torsion bar with different numbers of laminae. Results show that in the design of a laminated torsion bar it is necessary to consider correction coefficients with respect to the geometry of laminae and the clamping conditions on both sides of the laminated torsion bar. In this paper the correction coefficients are experimentally determined. We present the procedure for determination of correction parameters for the calculation of the laminated torsion spring characteristics with a relatively large ratio of width and thickness, (h/b > 7) for low rigidity of the individual lamella

Influence of Variable Support Conditions on Topology Optimization of Load-Carrying Parts

The paper addresses the importance of proper modeling of boundary conditions in preparing a FEA model for topology optimization of load-carrying structural parts. More specifically, the focus is on possible variations of support conditions during the service life of a structural part. Such variations emerge from various reasons, for example, from a fixing screw becoming loose. Since such variations are not deterministic and may cause the structural part to operate within a wide range of various conditions, this paper aims to improve the insight into this problem and to suggest a way to mitigate it. For this purpose, a bracket intended to carry a hydraulic motor is used as a test example and the topology of its design is optimized under various support conditions. The results are then analyzed in order to evaluate the consequences, caused by variations of the supports. Furthermore, a novel optimization procedure scheme is proposed based on selective load cases activity. This procedure aims to reduce the computational effort that may otherwise increase by an order of magnitude due to addition of all possible support variations. It is shown that adequate preparation of load cases that include all possible support conditions is of extreme importance since otherwise the part may behave badly in practical application even if its design looks to be quite reasonable. The new proposed optimization procedure also proves to reduce the needed computational effort substantially

Model for fatigue lifetime prediction of torsion bars subjected to plastic presetting

Prednaprezanje torzijskog štapa je uobičajena metoda za povećanje elastičnog kuta uvijanja i zakretnog momenta, ali ono skraćuje vijek trajanja do zamora. Opruge se koriste kao prigušivači kod strojeva s gusjenicama. Opruge, napravljene od sitno zrnatog čelika visoke čvrstoće, klase VCN, omogućuju visoki nivo absorbirane energije. Svaka i najmanja promjena tijekom postupka prednaprezanja ima veliki utjecaj na vijek trajanja do zamora. Unutar istog opterećenja, opruge mogu pokazati nisko ili visoko cikličko ponašanje na zamor u odnosu na različite stupnjeve prednaprezanja. Na osnovi izvršenih ispitivanja predlaže se model za vijek trajanja do zamora i nivoe smičnog naprezanja. Uzimajući u obzir provedena ispitivanja na zamor, moguće je optimizirati geometriju torzijskog štapa kako bi izdržao željeni broj ciklusa.The torsion presetting of a spring-bar is a common technique for extending the elastic twist-angle and increasing torque, but it reduces fatigue lifetime. Spring-bars are used as shock absorbers in caterpillar machines. Spring-bars, made from high strength fine-grain steel, grade VCN, provide a high level of absorbed energy. Any slight change in the presetting procedure has a strong influence on fatigue-lifetime. Within the same loading range, springs can exhibit low-cyclic or high-cyclic fatigue behavior regarding different presetting levels. A model for fatigue-lifetime and shear-stress levels is proposed on the basis of performed tests. Considering prescribed fatigue tests, it is possible to optimize a spring bar\u27s geometry, in order to survive the required number of cycles

Model for fatigue lifetime prediction of torsion bars subjected to plastic presetting

Prednaprezanje torzijskog štapa je uobičajena metoda za povećanje elastičnog kuta uvijanja i zakretnog momenta, ali ono skraćuje vijek trajanja do zamora. Opruge se koriste kao prigušivači kod strojeva s gusjenicama. Opruge, napravljene od sitno zrnatog čelika visoke čvrstoće, klase VCN, omogućuju visoki nivo absorbirane energije. Svaka i najmanja promjena tijekom postupka prednaprezanja ima veliki utjecaj na vijek trajanja do zamora. Unutar istog opterećenja, opruge mogu pokazati nisko ili visoko cikličko ponašanje na zamor u odnosu na različite stupnjeve prednaprezanja. Na osnovi izvršenih ispitivanja predlaže se model za vijek trajanja do zamora i nivoe smičnog naprezanja. Uzimajući u obzir provedena ispitivanja na zamor, moguće je optimizirati geometriju torzijskog štapa kako bi izdržao željeni broj ciklusa.The torsion presetting of a spring-bar is a common technique for extending the elastic twist-angle and increasing torque, but it reduces fatigue lifetime. Spring-bars are used as shock absorbers in caterpillar machines. Spring-bars, made from high strength fine-grain steel, grade VCN, provide a high level of absorbed energy. Any slight change in the presetting procedure has a strong influence on fatigue-lifetime. Within the same loading range, springs can exhibit low-cyclic or high-cyclic fatigue behavior regarding different presetting levels. A model for fatigue-lifetime and shear-stress levels is proposed on the basis of performed tests. Considering prescribed fatigue tests, it is possible to optimize a spring bar\u27s geometry, in order to survive the required number of cycles

Comparison between Stereo Optical Strain Measurements and Finite Element Results in Stress Concentration Zones

Experimental testing and deformation measurements during static loading in areas with high gradients are usually accompanied by uncertainties and inaccuracies of the applied methods. Comparison between different experimentally determined deformations and numerical calculation results of deformations at the determined measured points could be used to determine sensitivities and suitability of the particular measurement method for small deformations and pronounced levels of plastification. The paper presents analysis of combined deformation measurement methods with strain gauges and stereo-optical methods near the fatigue crack on the specimen during tensile loading. The results show that strain gauges are suitable for measurements at smaller deformations as applied for monitoring deformations during fatigue crack propagation. The stereo optical methods are suitable for measurements when significant elastic deformations occur, i.e. near the yield point, during static testing with plastic deformations and material fracture

Tlačno prednaprezanje cjevastih torzijskih opruga

This paper reports the results of a series of biaxial static compression and torsion experiments performed to evaluate the effects of static compression stress on the fatigue life of those smooth tubes made of high strength spring steel. The fatigue life of biaxial loaded springs depends, among others, on biaxial compression and torsion loading. A high shear loading ratio leads to low-cycle fatigue behaviour rather than high-cycle fatigue, because it was found that a crack was initiated at a local highly deformed area on surface of the specimen. The experimentally obtained results show a significant extension of fatigue strain life as a result of combining axial compression loading with torsion. Cracking behaviour was observed and it was noted that compression pre-stresses contribute to retardation of the fatigue crack initiation process and, consequently, contribute to the extension of fatigue life.U ovom se radu iznose rezultati niza eksperimenata dvoosnog statičkog tlačnog i torzijskog opterećenja kako bi se procijenilo djelovanje omjera tlačne napetosti na zamorni vijek trajanja cijevi napravljenih od visoko čvrstog čelika za opruge. Vijek trajanja dvoosno opterećenih opruga obzirom na zamor ovisi, između ostaloga, o biaksijalnom tlačnom i torzijskom opterećenju. Omjer opterećenja kod visokog smičnog naprezanja dovodi do nisko cikličkog više nego visoko cikličkog zamora jer se ustanovilo da se pukotina pojavila na lokalnom krajnje deformiranom dijelu na površini uzorka. Eksperimentalno dobiveni rezultati pokazuju značajan produžetak vijeka trajanja deformacije zbog zamora kao rezultat kombiniranja aksijalnog tlačnog i torzijskog opterećenja. Primijećena je pojava pukotina i zapaženo da tlačna prednaprezanja dovode do usporavanja procesa nastajanja zamornih pukotina i stoga doprinose produženju vijeka trajanja obzirom na zamor

Tensile test models for low-carbon microalloyed steels with high niobium contents

U ovom se istraživanju proučavao utjecaj parametara valjanja (2 redukcijske brzine i 3 brzine hlađenja) i kemijskih elemenata kao što su: C, Mn, Nb, Ti, Mo, Ni, Cr, Cu i B na svojstva čvrstoće niskougljičnih mikrolegiranih čelika s visokim sadržajem niobija (do 0,12 wt. % Nb). U tu je svrhu konstruiran pokusni uređaj zasnovan na inteligentnom dizajnu eksperimenata (DoE), rezultirajući s 26 odljevaka (laboratorijskih odljevaka). Kombinacijom metalografije, Electron Back-Scattered Diffraction (EBSD) i vlačnih ispitivanja proučavalo se kako obradni parametri i kemijski sastav djeluju na čvrstoću. Kada je ispitivanje rezultiralo naprezanjem, rasteznom čvrstoćom, jednoličnom deformacijom ili deformacijom zbog loma, rezultati su statistički analizirani tehnikom višestrukelinearne regresije, koja je dovela do odgovarajućih jednadžbi. Ustanovilo se da se učinak niobija na povećanje čvrstoće smanjuje kako se povećava sadržaj ugljika.In the present investigation, the effect of both: rolling parameters (2 reduction rates and 3 cooling rates) and chemical elements such as: C, Mn, Nb, Ti, Mo, Ni, Cr, Cu and B, has been studied in relation to strength properties in low-carbon microalloyed steels with high niobium contents (up to 0,12 wt. % Nb). For this purpose, an experimental set-up was designed based on an intelligent design of experiments (DoE), resulting in 26 casts (laboratory casts). A combination of metallography, Electron Back-Scattered Diffraction (EBSD) and tensile tests have been performed to study how processing parameters and chemical composition affect the strength. The results, where the proof stress, tensile strength, uniform and fracture elongations are the response variables, have been analysed statistically by means of multiple linear regression technique, leading to response equations. From the results, it was found that the effectiveness of niobium increasing the strength is reduced as carbon content increases

Model za predviđanje zamornog vijeka trajanja torzijskih štapova podvrgnutih plastičnom prednaprezanju

The torsion presetting of a spring-bar is a common technique for extending the elastic twist-angle and increasing torque, but it reduces fatigue lifetime.Spring-bars are used as shock absorbers in caterpillar machines. Spring-bars, made from high strength fine-grain steel, grade VCN, provide a high level of absorbed energy. Any slight change in the presetting procedure has a strong influence on fatigue-lifetime. Within the same loading range, springs can exhibit low-cyclic or high-cyclic fatigue behavior regarding different presetting levels. A model for fatigue-lifetime and shear-stress levels is proposed on the basis of performed tests. Considering prescribed fatigue tests, it is possible to optimize a spring bar\u27s geometry, in order to survive the required number of cycles.Prednaprezanje torzijskog štapa je uobičajena metoda za povećanje elastičnog kuta uvijanja i zakretnog momenta, ali ono skraćuje vijek trajanja do zamora. Opruge se koriste kao prigušivači kod strojeva s gusjenicama. Opruge, napravljene od sitno zrnatog čelika visoke čvrstoće, klaseVCN, omogućuju visoki nivo absorbirane energije. Svaka i najmanja promjena tijekom postupka prednaprezanja ima veliki utjecaj na vijek trajanja do zamora. Unutar istog opterećenja, opruge mogu pokazati nisko ili visoko cikličko ponašanje na zamor u odnosu na različite stupnjeve prednaprezanja. Naosnovi izvršenih ispitivanja predlaže se model za vijek trajanja do zamora i nivoe smičnog naprezanja. Uzimajući u obzir provedena ispitivanja na zamor, moguće je optimizirati geometriju torzijskog štapa kako bi izdržao željeni broj ciklusa