Application of Thermography in Analysis of Fatigue Strength of Materials and Structures

Termografija, kao nerazorna metoda, ima sve veću primjenu u istraživanjima i industriji. U radu je prikazana primjena termografije u procjeni koncentracije naprezanja te zamora materijala i konstrukcija. Na primjerima uzoraka s koncentratorima naprezanja prikazana je primjena termografije u analizi metalnih materijala. U tu svrhu uspoređeni su rezultati klasičnih ispitivanja na umarlici s tri termografske metode: termoelastičnom analizom naprezanja, Risitanovom metodom te metodom praćenja širenja zone plastifikacije i loma. Termoelastičnom analizom naprezanja na ciklički opterećenim uzorcima dobiva se raspodjela naprezanja te koncentracije naprezanja na površini materijala. Risitanova metoda na temelju mjerenja porasta temperature ciklički opterećenog uzorka s porastom opterećenja predviđa dinamičku čvrstoću uzorka. Zbog velike disipacije topline u zoni plastifikacije i pukotine, brze srednjovalne kamere omogućuju praćenje tijeka plastifikacije i širenja pukotine. Opisane metode primjerene su za dinamička ispitivanja, nerazorne su i beskontaktne te ne utječu na rezultate ispitivanja.Thermography is becoming more and more relevant method in industry and as a research tool. It is an accepted method in many fields where non-destructive testing is carried out. In this paper focus was on evaluation of stress concentrations and fatigue of metal structures. Three thermographic methods: Thermoelastic stress analysis, Risitano method and acquisition of plastification zone and fracture propagation, are addressed and compared with results of classical cyclic testing of Al2024 alloy specimens. Specimens with three types of stress concentrator are used; 3 mm triangular notch, R3 mm circular notch, and a hole with 6 mm diameter. All thermographic methods showed high level of coincidence with classical fatigue tests. Thermoelastic stress analysis provides first stress invariant field for cyclic loaded sample, revealing stress concentrations near notches. Risitano method, from thermal dissipations at various levels of cyclic load, estimates dynamic strength of materials. Fast cooled middle-wave infrared cameras enable locating and tracing material plastification and fracture propagation. The outcomes of all evaluated methods are in accordance with each other

Application of Thermography in Analysis of Fatigue Strength of Materials and Structures

Termografija, kao nerazorna metoda, ima sve veću primjenu u istraživanjima i industriji. U radu je prikazana primjena termografije u procjeni koncentracije naprezanja te zamora materijala i konstrukcija. Na primjerima uzoraka s koncentratorima naprezanja prikazana je primjena termografije u analizi metalnih materijala. U tu svrhu uspoređeni su rezultati klasičnih ispitivanja na umarlici s tri termografske metode: termoelastičnom analizom naprezanja, Risitanovom metodom te metodom praćenja širenja zone plastifikacije i loma. Termoelastičnom analizom naprezanja na ciklički opterećenim uzorcima dobiva se raspodjela naprezanja te koncentracije naprezanja na površini materijala. Risitanova metoda na temelju mjerenja porasta temperature ciklički opterećenog uzorka s porastom opterećenja predviđa dinamičku čvrstoću uzorka. Zbog velike disipacije topline u zoni plastifikacije i pukotine, brze srednjovalne kamere omogućuju praćenje tijeka plastifikacije i širenja pukotine. Opisane metode primjerene su za dinamička ispitivanja, nerazorne su i beskontaktne te ne utječu na rezultate ispitivanja.Thermography is becoming more and more relevant method in industry and as a research tool. It is an accepted method in many fields where non-destructive testing is carried out. In this paper focus was on evaluation of stress concentrations and fatigue of metal structures. Three thermographic methods: Thermoelastic stress analysis, Risitano method and acquisition of plastification zone and fracture propagation, are addressed and compared with results of classical cyclic testing of Al2024 alloy specimens. Specimens with three types of stress concentrator are used; 3 mm triangular notch, R3 mm circular notch, and a hole with 6 mm diameter. All thermographic methods showed high level of coincidence with classical fatigue tests. Thermoelastic stress analysis provides first stress invariant field for cyclic loaded sample, revealing stress concentrations near notches. Risitano method, from thermal dissipations at various levels of cyclic load, estimates dynamic strength of materials. Fast cooled middle-wave infrared cameras enable locating and tracing material plastification and fracture propagation. The outcomes of all evaluated methods are in accordance with each other

Fatigue Failures in Industry and Their Repairs – Case Studies

In spite of numerous and expensive researches in the field of fatigue, cracks and failures caused by fatigue occur every day in all fields of human activity. The paper presents some typical fatigue damages in industry and transport. Fatigue failure of the main engine lateral support (at bulk carrier), fatigue cracks on the large portal crane, and fatigue cracks and failures of the large gear wheel of the cement mill are described. The complete fatigue damage analysis and repair procedures are presented, too

Failure analysis of the rolls with grooves

he failure analysis of the rolls with grooves on the 3-high-roughing mill stand for hot rolling is presented. Detailed analysis of all the elements which influenced the failure was carried out, namely: the position and the place of all failures are determined and all fracture surfaces are described; the rolling forces are determined by analytical and experimental methods; numerical analysis of the local stresses due to rolling forces is performed with finite element method; stress time history of the individual local stress and stress spectrum are obtained from service loads; prop- erties of the roll material (strength, hardness, toughness and ductility) is determined by experimental testing. Based on the results of investigation, main causes of failures are presented

The Application of Pulsed Thermography Image Processing Method to Longwave Bolomteric Infrared Cameras

Pulsed infrared thermography is a NDT method for evaluating polymer reinforced structures. As our former research was performed on advantageous cooled middle-wave camera, in this contribution gradient based image processing method has been applied on long-wave bolometric cameras. Different wavelengths and camera sensitivities have been compared on prefabricated specimen. To demonstrate the capability of approach, examples from floating vehicles industry have been presented

Fatigue Failures in Industry and Their Repairs – Case Studies

In spite of numerous and expensive researches in the field of fatigue, cracks and failures caused by fatigue occur every day in all fields of human activity. The paper presents some typical fatigue damages in industry and transport. Fatigue failure of the main engine lateral support (at bulk carrier), fatigue cracks on the large portal crane, and fatigue cracks and failures of the large gear wheel of the cement mill are described. The complete fatigue damage analysis and repair procedures are presented, too

The Application of lR Thermography to the NDT and Thermal Stress Analysis

Advantages of using Infrared Thermography as a Non Destructive Testing method is resulting in the growing interest for method in the field of composite structures. The presented research is focused on Glass Reinforced Polymer structures. Methods, such as Pulse Thermography, Pulsed Phase Thermography and Lock-in Thermography are re-ferred. The Pulse Thermography together with the gradient based approach is addressed for the case of wind turbine blades. The gradient based image processing approach enables filtering out anomalies with the goal to make clearer distinction and evaluation. The Ther-moelastic Stress Analysis, as a method similar to the Lock-In Thermography, is presented as an NDT approach for evaluating stress distribution of cyclic loaded structures

Crush performance of multifunctional hybrid foams based on an aluminium alloy open-cell foam skeleton

Multifunctional hybrid foams were developed and tested by combining aluminium alloy open-cell (OC) foam specimens with polymers, epoxy resin and silicone rubber. The rectangular OC foam specimens were impregnated with polymer, completely filling the voids. The aim of this work was to evaluate the effect of the polymer presence in the voids of aluminium alloy OC foam specimens (varying their size, e.g. height to width ratio) on the crush performance of the resulting hybrid foams. Quasi-static and dynamic uniaxial compressive tests and infrared thermography were used to compare the behaviour of hybrid foams with conventional (unfilled) OC foam specimens. Results show an improvement of the compressive strength and energy absorption capacity of hybrid foams, especially when infiltrated with epoxy resin. The results show that the epoxy leads to higher capacity of specific energy absorption of the hybrid foams, while silicone leads to lower capacity of specific energy absorption in comparison to the OC foam specimens. The high energy absorption values of OC foams embedded with silicone are not enough to compensate for the mass increase due to the silicone filler. The use of the polymers as a void filler changes the typical layer-wise collapse mechanism of the OC foam. The silicone rubber causes a non-symmetric deformation, being much more complex and unstable in the case of the longer hybrid foams, which deform by buckling (lateral instability). The epoxy resin enforces a symmetric deformation by folding in the middle of the hybrid foams.publishe

Bending performance evaluation of aluminium alloy tubes filled with different cellular metal cores

A comprehensive bending performance and energy absorption capability of aluminium alloy tubes filled with different cost-effective cellular metal cores were experimentally evaluated for the first time. The following cellular metal cores were evaluated: i) Advanced Pore Morphology (APM) foam, ii) hybrid APM foam and iii) Metallic Hollow Sphere Structures (MHSS). The results have been compared also with the performance of aluminium alloy tubes filled with (ex-situ and in-situ) closed-cell aluminium alloy foam. The three-point bending tests have been performed at two loading rates (quasi-static and dynamic) and supported by infrared thermography to evaluate the deformation mechanism, damage progress and failure modes. A thorough heat treatment sensitivity (due to the fabrication procedures of composite structures) study on the aluminium tubes has been performed as well. The results show that a reliable and predictable mechanical behaviour and failure can be achieved with proper combination of tubes and cellular metal core. A low scatter of bending properties and energy absorption capability has been observed. The hybrid APM and the ex-situ foam filled tubes achieved the highest peak load. However, they also exhibit a rapid load drop and abrupt failure once the structure has reached the peak load. The APM, MHSS and in-situ foam filled tubes show more ductile behaviour with a predictable failure mode.publishe

Mechanical, thermal, and acoustic properties of aluminum foams impregnated with epoxy/graphene oxide nanocomposites

Hybrid structures with epoxy embedded in open-cell aluminum foam were developed by combining open-cell aluminum foam specimens with unreinforced and reinforced epoxy resin using graphene oxide. These new hybrid structures were fabricated by infiltrating an open-cell aluminum foam specimen with pure epoxy or mixtures of epoxy and graphene oxide, completely filling the pores. The effects of graphene oxide on the mechanical, thermal, and acoustic performance of epoxy/graphene oxide-based nanocomposites are reported. Mechanical compression analysis was conducted through quasi-static uniaxial compression tests at two loading rates (0.1 mm/s and 1 mm/s). Results show that the thermal stability and the sound absorption coefficient of the hybrid structures were improved by the incorporation of the graphene oxide within the epoxy matrix. However, the incorporation of the graphene oxide into the epoxy matrix can create voids inside the epoxy resin, leading to a decrease of the compressive strength of the hybrid structures, thus no significant increase in the energy absorption capability was observed.publishe