Željko Božić

University of Zagreb · Faculty of Mechanical Engineering and Naval Architecture, Dept. of Aeronautical Engineering

This study investigates the influences of the critical resolved shear stress (CRSS) values on calculating the number of cycles for the fatigue crack initiation cycle of X10CrMoVNb9-1 (P91) under cyclic loading conditions at room temperature while considering varied surface roughness on microstructure models. The micropillar compression test was uti...

Three-parameter optimisation of a wing-fuselage attachment lug was applied to its thickness, rounding radius, and radius of pin hole, using the fatigue life and mass as criteria. Numerical simulation of fatigue crack growth by finite element method (FEM) and Separating Morphing and Adaptive Remeshing Technology (SMART) was used to evaluate the numb...

https://authors.elsevier.com/a/1iZEnWK0QbniP

The Locati method for accelerated fatigue testing can be successfully applied in preliminary fatigue testing of components and in production quality control. The method uses only one test sample and assumes that the slope of the S-N curve is known a priori. In this paper, a modified Locati method is presented in which the initial approximation of t...

The damage caused by impact of hard particles on aircraft components is called Foreign object damage (FOD) and it may cause premature failure. 7075-T6 is one of the alloys frequently used for manufacturing aircraft parts and components. In this paper, the failure mechanism of a damaged 7075-T6 specimen subject to rotating bending was explained from...

Modeling fiber-reinforced concrete at failure by fracture is a challenging task because we need insight into the post-peak behaviour of the model after failure, including crack propagation. In this paper, we present the basic properties of the fiber-reinforced concrete model and its ability to capture the phenomena in three-point bending tests. In...

In this study, an analytical method for fast spectral fatigue-life prediction under Broad-Band random loading is proposed. It is based on the power spectral density of stress in the structure and the Rice peak stress distribution of a stationary Gaussian random process. The novel simple closed-form solution employs special HyperGeometric function w...

The significant increase in applications of Additive Manufacturing (AM) has led to various investigations in this field. Three-dimensional (3D)-printed parts might be subjected to different environmental conditions during their service life. Therefore, a profound knowledge on this subject can significantly help to increase structural performance of...

Thrust bearings are undoubtedly one of the essential parts of turbines and compressors. However, there are many cases in which asymmetric load occurs on the bearings due to e.g. thermal deformations, production inaccuracies or a simple deflection of the shaft. The presented research deals with some basic steps involved in comprehensive research rel...

The aircraft industry is a leading industry in terms of the implementation of new materials and technologies. In the development of a light aircraft several different materials were considered for the engine cover design and the final decision was to select a composite material. Part of the research performed on the cover design is presented in thi...

Corrosive marine environment has negative impact on welded steel structures, so it is necessary to investigate the effect of sea exposure on such materials. This research investigates the change of mechanical properties and surface condition of AH36 shipbuilding steel butt-welded specimens exposed to natural marine environment for prolonged periods...

Additive technology has recently grown from experimental rapid prototyping to the production of functional engineering components for various applications, but the inherent quality of additive manufacturing and significantly weaker mechanical properties in comparison with traditional manufacturing still limit their application. Hence, a modified fu...

Fatigue crack growth in orthopaedic locking compression plates (LCP), under four-point bending, has been simulated by the extended finite element method (xFEM) to assess LCP optimal geometry in respect to remaining life. Loads corresponded to those occurring in human tibia during gait cycle for different body weights (60, 90 and 120 kg). Experiment...

Failure and fatigue life prediction becomes more important for design of composite marine vessels and structures as their application as constructive material increases. Harsh environmental operational conditions have a great impact on such structures. Realistic environmental input parameters for structural modeling of marine structures are crucial...

Mechanical behaviour of butt-welded joint specimens made of AH36 shipbuilding steel exposed to real marine environment for prolonged periods is analyzed experimentally and numerically in this paper. After the specimens were extracted from experiment site, standardized tensile tests have been performed along with the Charpy impact and hardness tests...

The progress of additive manufacturing technology brings many new questions and challenges. Additive production technology allows the design of machine elements with less mass, but at the same time with the same stiffness and load capacity. By using additive manufacturing, it is possible to produce gears in the form of shell shape with infill insid...

This study is dealing with the effect of the grain size on the fatigue lifetime of metallic components, which is represented in the form of (S-N) Wöhler curves of two different grain sizes. The micro-models containing the microstructures of the two different grain sizes are handled by employing the Finite Element Method (FEM) and the required numbe...

The article deals with the specification of the most suitable machining parameters for three newly designed end mills in the term of stability of the deep groove machining, at which the depth of cut is minimally twice higher the diameter of the cutter. Online vibration analysis was selected as a tool for goal achievement. The partial objective of t...

In this work, Design of Experiments is applied to identify which factors mostly influence the residual stress distribution in an hourglass specimen subject to the impact of a foreign object. The specimen is made of 7075-T6, that is one of the most popular alloys in the aeronautical sector. After the impact, the specimen is assumed to be tested with...

Plain bearings are undoubtedly one of the main parts of the power machines (such as a turbine or compressor). However, there are many cases when in large power equipment is occurring asymmetrically loading on bearings due to thermal deformations, production inaccuracies, or simple deflection of the shaft. Presented research deals with the numerical...

Fracture properties of various types of concrete, like plain or fiber reinforced concrete are determined in 3-point bending experiments resulting in a force-displacement diagram. Standard properties of concrete are then determined using technical norms. However, post-peak behavior of concrete, including crack propagation, cannot be described using...

The automotive industry has been making a strong shift toward electrically powered vehicles lately. Electric traction motors, needed for such an application, should have high power density, high efficiency and last but not least, a reliability. The permanent magnet synchronous motor (PMSM), was originally designed as a traction motor for a full ele...

A closed-form explicit solution for statistical fatigue life assessment under broad-band stochastic loading is proposed herein. Obtained solution is valid for stationary, random and ergodic zero mean Gaussian stress process. It is based on Rice/Lalanne peak stress probability distribution function. The solution is given in terms of special Gaussian...

The blades of axial turbomachines (steam and gas turbines, axial compressors) are highly stressed by centrifugal force, temperature, and alternating fluid forces, which leads to vibrations and fatigue cracking. This requires the studious engagement of designers and technologists. In this paper, a procedure for accelerated fatigue testing of a gas t...

In this paper determination of mechanical properties of composite material using experimental and numerical approach is presented. The mechanical properties of a laminate obtained in the experiment are used for verification of numerically obtained values, as well as estimation of the load-carrying capacities of composite engine cover of light aircr...

This paper presents an analytical study on stability and performance of supercritical linear active vibration isolation systems. The systems analyzed are consisted of source and receiving bodies. Receiving body is to be protected from vibrations. Supercritical scheme means that the uncoupled natural frequency of the receiving body is smaller than t...

Additive manufacturing of polymers results in low strength and inherently defective parts with limited application, hence the reason for selectively reinforcing the material using continuous fibers for improving the mechanical properties for which there are indications deviation from the classical laminate theory (CLT) theory and the rule of mixtur...

The aim of the paper is to investigate the influence of compressive residual stresses on the fatigue initiation life (S-Nini) curve of AISI 1141 steel. The analysis has been performed by means of a micro-structurally-based fatigue crack initiation modelling approach. The focus is set on the local (surface) residual stresses typically imposed by a s...

The indentation test is one of the most commonly employed techniques for the characterization of mechanical properties of materials. It is an efficient and useful tool for the evaluation of mechanical properties of small volumes of materials, e.g., hardness, elastic modulus and fracture toughness, etc., through analyzing the relationship between co...

Spiral bevel gear, used in a crane drivetrain, experienced wear, damage and fracture during standard operation. Experimental and numerical procedures were combined to determine the origins of the failure. Experimental procedures consisted of visual examination of the gear, optical and electron microscopy of the teeth, analysis of chemical compositi...

Fatigue life of a loosened total hip prosthesis femoral component cemented into bone was investigated assuming loads specified by the standard ISO 7206-4. The total hip prosthesis CAD model was developed by implementing a 3D scanning procedure. Based on the created CAD model, the FE model was developed. A linear elastic analysis was carried out for...

Failures of rotating equipment often cause severe consequences, so it is necessary to study their integrity and life as detailed as possible, especially when crack is detected. In the case studied here, hydro power plant turbine shaft is analysed by using fracture mechanics parameters both for static and dynamic loading in order to assess its struc...

This paper is a continuation of our work on modelling and parameter identification in fibre reinforced concrete with steel fibres. The main characteristic of this material in failure is that fibres do not break but get pulled-out of the concrete matrix and the bond between the fibre and the matrix (bond-slip law) strongly influences the behaviour i...

The 7075-aluminum alloy is often used in aerospace, automotive, and maritime sectors owing to its high strength-to-weight ratio. Application of Physical Vapor Deposition (PVD) coating has proved to increase tribological properties and corrosion resistance. However, the effects of these coatings on the fatigue strength of coated materials remain to...

The research presented in this paper is based on the use of extended finite element method (XFEM) for stress intensity factors (SIFs) determination in the case of fatigue crack presented in the wing-fuselage attachment lug used in light aerobatic aircraft. The presence of the through crack at the attachment lug hole is not allowed since its growth...

The paper presents strain-based fatigue assessment of the rotating demining tiller tool. In order to make a cost reduction, the idea was to replace initially applied high strength steel with unalloyed structural steels. To maintain the same or almost the same durability, the original geometry needed to be improved. The LCF theory was chosen as the...

The exhaust nozzle represents a part of a jet engine which is crucial to its overall performance, since it accelerates the flow of hot gases out of the engine and creates a thrust. During its long service, it is exposed to elevated temperatures and high compressive and hoop stresses, which makes the cracks’ occurrence in the exhaust nozzle’s inner...

Crack propagation in 3PB specimen has been investigated experimentally by using Digital Image Correlation (DIC) technique. For this purpose, specimens were taken from butt welded plates, made of P460NL1 micro-alloyed steel. Fatigue pre-crack of 3PB specimens was introduced in the weld metal. Specimens were then statically loaded and analyzed using...

Due to the worldwide decrease in the quantity of potable water in the last decade, the desalination station is among one of the most important methods to treat seawater to supply the dry regions, Sahara regions and the offshore regions with purified water. During the desalination process, many problems can appear including the corrosion problems th...

Puffiness formation can occur during process of pipelines component fabrication and transportation or during construction, operation, maintenance and their repair processes. The present paper addresses issues related to pipeline design and associated with the unintended actions due to external loads or ground movements. These may introduce longitud...

The paper analyzes plastic limit loads for cracked tubes containing twin collinear axial through-wall cracks under internal pressure. Calculations of these loads are based on small strain finite element limit analysis using elastic-perfectly plastic materials. Flow stress as the average value of the yield stress and the ultimate tensile strength wa...

This paper presents an analytical analysis and optimization of vibration-induced fatigue in a generalized, linear two-degree-of-freedom inerter-based vibration isolation system. The system consists of a source body and a receiving body, coupled through an isolator. The isolator consists of a spring, a damper, and an inerter. A broadband frequency f...

On the basis of the calculation of the stress field around the corrosion-damaged areas on the external part of a pipeline used for the transport of hydrocarbons, an analysis of the effect of the level of post-repair burst pressure by composite patches is proposed. This work examines some points of views on the burst pressure standards calculation o...

Due to its remarkable strength-to-weight ratio, the bimodal Ti-6Al-4V titanium alloy is widespread in high performance engineering sectors. Its good corrosion resistance is due to a surface oxide, which however can be damaged under cyclic loading and in harsh environments. This paper aims to clarify the fracture behavior of some specimens quasi-sta...

A reverse engineering procedure based on optical 3D scanning was implemented to generate a total hip prosthesis CAD model needed to create the finite element model of the femoral component cemented into cortical bone. Finite element fracture analyses of a loosened femoral component shaft of the total hip prosthesis damaged with a crack was performe...

The aim of this study is to analytically and numerically model the vibration-induced helical spring fatigue in a generalized vibration isolation system. The system consists of a receiving body and a dynamically active base coupled through a passive isolator. The isolator consists of a coupling helical spring and an inerter. System inherent damping...

This paper presents an optimization and numerical analysis of vibration-induced fatigue in a two degree-of-freedom inerter-based vibration isolation system. The system is comprised of a primary, e.g. source body, and a secondary, e.g. receiving body, mutually connected through an isolator. The isolator includes a spring, a dashpot and an inerter. I...

The primary objective of the single tooth fatigue test is to generate gear-tooth bending fatigue data at a comparatively low price. Assuming a negligible influence on fatigue data, the effect of friction is not evaluated. The aim of this study is to evaluate the effect of tooth friction on tooth bending fatigue life and on the location of the crack...

This paper deals with the initiation of a short crack and subsequent growth of the long crack in a carbon steel under cyclic loading, concluded with the estimation of the complete lifetime represented by the Wöhler (S-N) curve. A micro-model containing the microstructure of the material is generated using the Finite Element Method and the according...

The structural strength of a total hip prosthesis was investigated based on a 3D scanning procedure of a hip prosthesis and Finite Element Analysis. 3D scanning was performed by the ATOS 3D scanner, and the CAD model was built using Geomagic Design X software. The obtained CAD model was imported to Finite Element simulation software Abaqus to gener...

This paper presents a method for predicting fatigue crack propagation in welded stiffened panels accounting for the effects of residual stresses. Well known power law models were employed to simulate fatigue life for a welded stiffened panel specimen damaged with a central crack. Stress intensity factor values (SIF) were obtained in finite element...

For most engineering alloys, the long fatigue crack growth under a certain stress level can be described by the Paris law. The law provides a correlation between the fatigue crack growth rate (FCGR or da/dN), the range of stress intensity factor (ΔK), and the material constants C and m. A well-established test procedure is typically used to determi...

The axle pin is one of the most critical components of a wind turbine. Because 2 bearings are mounted on the axle pin, it is not subjected to torque and is designed only to carry bending stresses. The axle is usually made by a casting process, which can induce defects. After casting of the axle pin, radial surface cracks were detected outside by ul...

This paper deals with the modelling of short crack initiation within a microstructure of medium carbon steel under fatigue loading, as well as with the influence of overload on the crack initiation period. Studies on the long crack growth show that the overload introduces first an increase in the crack growth rate that is then followed with a decre...

The influence of welding residual stresses in stiffened panels on effective stress intensity factor values and fatigue crack growth rate is studied in this paper. Interpretation of relevant effects on different length scales such as dislocation appearance and microstructural crack nucleation and propagation are taken into account using Molecular Dy...

Numerical modelling and simulations were carried out in order to analyze fracture mechanisms for stiffened panels, damaged by a single and multiple cracks, and subjected to lateral pressure. For that purpose finite element models for stiffened panel specimens were developed using shell elements. Material property data used in the simulation were ob...

The influence of welding residual stresses in stiffened panels on effective stress intensity factor (SIF) values and fatigue crack growth rate is studied in this paper. Interpretation of relevant effects on different length scales such as dislocation appearance and microstructural crack nucleation and propagation is taken into account using molecul...

The influence of welding residual stresses in stiffened panels on effective stress intensity factor values and fatigue crack growth rate was studied in this paper. Interpretation of relevant effects on different length scales such as dislocation appearance and microstructural crack nucleation and propagation are taken into account using Molecular D...

This paper presents the implementation of fatigue crack growth power law equations based on ΔK, ΔJ-integral and ΔCTOD fracture mechanics parameters determined in an FE analysis, to plates with multiple site damage (MSD). Results of fatigue tests with constant amplitude tensile loading carried out on mild steel plate specimens damaged with a single...

This paper presents the developed fatigue crack growth models based on parameters Delta K, Delta J-integral and Delta CTOD determined by using linear elastic and elastic plastic FE analysis. The fatigue crack growth threshold values of the considered crack growth driving force parameters, below which crack propagation does not occur, were taken int...

Supervising and health monitoring of structures can assess the actual state of existing structures after initial loading or in the state of operation. Structural life management requires the integration of design and analysis, materials behavior and structural testing, as given for several examples. Procedure of survey of structural elements and cr...