Katia Casavola

Politecnico di Bari, DMMM - Mechanical Mathematical and Management Department, Faculty Member

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From 2005, Prof. Casavola works in the field of Mechanical Design (SSD ing-ind/14) at the Engineering School I of the Politecnico di Bari. She teached Experimental Mechanics I (undergraduate course) and Mechanical Behaviour of Materials (graduate course). She teached also Engineering Techniques 2 at the Architectural Faculty of Politecnico di Bari. Prof. Casavola is full professor of Mechanical Design (SSD ING-IND/14) at the Engineering School I of the Politecnico di Bari and she teaches Design and Experimentation of Innovative Materials (graduate course).
Prof. Casavola’s research activity is concerned with mechanical characterization of materials (steel, aluminium alloy, titanium alloy, aluminium foam sandwich, composite materials, sintered materials, polymeric and biodegradable materials), fatigue and fracture of metallic materials, mechanical strength of welded structures, experimental stress analysis, residual stress measurements, thermal and thermo-mechanical analysis of welding cycles, monitoring of electronic board and components by means of speckle interferometry.
Prof. Casavola is in charge of the scientific management of Lab. of Mechanical Behavior of Materials, Lab. of Residual Stresses Measurements and Lab. of Experimental Stress Analysis and Lab. of Telemetry at Politecnico di Bari.

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Papers by Katia Casavola

Effects of process parameters on the residual stresses measurements on titanium plates by using ESPI

Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it ... more Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it is, at the moment, the only technique to be ruled by a standard. Many improvements were introduced along the years and recently research papers investigated the feasibility to use optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally speaking, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area, to be intended as the portion of the image captured by the CCD camera whose data are used to calculate the strain values, are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is investigated. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame up to 50% of the yield strength. Drilling speeds ranging between 5000 ÷ 50000 rpm were investigated by using an electronically controlled mill. Results obtained at different speeds and for different locations of the analysis area were compared with the theoretical expected value and with results from a numerical model implemented in ANSYS®.

Preparation of Explanted Coronary Stents for Investigation of Material Properties

Materials Today: Proceedings, 2016

The most commonly used treatment method for coronary artery disease is stent deployment, because ... more The most commonly used treatment method for coronary artery disease is stent deployment, because it has several advantages against the traditional heart surgery. The long-term follow-up of coronary stents is necessary, yet nearly three decades since the first stent was implanted in a human coronary artery and still a few publications deal with in vitro investigation of material properties of stents after their in vivo life. This work covers the preparation process of coronary artery stents explanted from human cadavers for further research. To determine the dissolution method several carotid arteries, coronary arteries and new stents were used. After evaluating the stereomicroscope, SEM and EDS results eight explanted artery segment were dissolved from twelve implanted stents.

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Caratterizzazione meccanica di nuovi materiali compositi “stitched/RFI

Scopo del presente lavoro è individuare le prestazioni meccaniche di un nuovo materiale composito... more Scopo del presente lavoro è individuare le prestazioni meccaniche di un nuovo materiale composito costituito da fibre lunghe a modulo standard e resina epossidica termoindurente tenacizzata. Tale composito è tessuto con vari layer, ciascuno contenente fasci di fibre paralleli ed affiancati tra loro secondo l’orientazione propria del layer stesso, sovrapposti e tenuti uniti mediante processo di cucitura delle preforme, successivamente impregnate con resina a caldo e sotto pressione (RFI). Al fine di simulare le condizioni di esercizio del materiale è stata condotta una campagna di prove meccaniche a caldo e ad elevata umidità relativa (71°C) per simulare un invecchiamento accelerato del materiale e le condizioni di lavoro delle parti di composito vicine ai motori, a freddo (-54°C) per simulare le condizioni di lavoro in volo, e a temperatura ambiente (23°C). Sono state eseguite diverse tipologie di prova: trazione, trazione open hole e filled hole, compressione, compressione open hole e filled hole, taglio, flessione, bearing con 1 e 2 fastners. Il confronto dei risultati tra le diverse temperature ha evidenziato gli effetti benefici del raffreddamento del materiale a -54°C, rispetto ai test condotti alle altre due temperature di prova ed ha inoltre mostrato che le caratteristiche di resistenza, contrariamente alle aspettative, non hanno risentito dell’aumentare della temperatura per via del comportamento stabile delle fibre di carbonio. L’analisi delle differenti tipologie di prova ha inoltre messo in evidenza che una maggiore percentuale di fibre lungo la direzione di prova conferisce al materiale migliori caratteristiche di resistenza.

Residual Stress on Aisi 300 Sintered Materials

Conference Proceedings of the Society for Experimental Mechanics Series, 2011

The hole-drilling method (HDM) is a convenient and effective method for measuring residual stress... more The hole-drilling method (HDM) is a convenient and effective method for measuring residual stresses near the surface of an isotropic linear-elastic material. The measurement procedure is relatively simple, and has been standardized in ASTM Standard Test Method E837. The HDM is also versatile and can be performed in laboratory or in situ, on components ranging widely in size and shape. It is often referred to as a "semidestructive" technique, since the small hole will not, in many cases, significantly impair the structural integrity of the part being tested. The basic principle was first introduced by Mathar in 1934. Since that time, many researchers have further developed the method, culminating in the establishment of a standardized procedure ASTM E837. At least three established methods are available for estimating non-uniform residual stress fields from relaxed strain data from the incremental HDM. They are the Power Series, the Integral and the ASTM E837-08 Methods. These methods rely on finite element calculated calibration data, utilize different approaches for stabilizing and smoothing the non uniform residual stress field, and do not have the theoretical shortcomings of the two traditional methods (the Incremental Strain and the Average Strain Methods). Since the strain variations during drill depends on many factors hardly predictable and checkable a priori, it seems that the best calculation method should be evaluated for each particular experiment. This paper compares the Power Series, Integral and ASTM E837-08 methods as procedures for determining non-uniform residual stress fields using strain relaxation data from the HDM. Specimens made of AISI Maraging 300 steel by means of Selective Laser Melting are investigated and the residual stress profiles performed by means of all three stress calculation procedures are also presented and compared.

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Residual Stress on Ti6Al4V Hybrid and Laser Welded Joints

Conference Proceedings of the Society for Experimental Mechanics Series, 2011

Ti6Al4V alloy combines mechanical strength, deformability, excellent fatigue and corrosion resist... more Ti6Al4V alloy combines mechanical strength, deformability, excellent fatigue and corrosion resistance and high strength to weight ratio. Furthermore, the mechanical behavior remains excellent at high temperature. Such characteristics make this material attractive for numerous applications (structural, aerospace and naval) because of recent improvements in welding techniques (laser, hybrid laser/MIG) that allow realizing high quality titanium welded joints. However some problems

Characterization and Prediction of Cracks in Coated Materials: Direction and Length of Crack Propagation in Bimaterials

International Scholarly Research Notices, 2015

The behaviour of materials is governed by the surrounding environment. The contact area between t... more The behaviour of materials is governed by the surrounding environment. The contact area between the material and the surrounding environment is the likely spot where different forms of degradation, particularly rust, may be generated. A rust prevention treatment, like bluing, inhibitors, humidity control, coatings, and galvanization, will be necessary. The galvanization process aims to protect the surface of the material by depositing a layer of metallic zinc by either hot-dip galvanizing or electroplating. In the hot-dip galvanizing process, a metallic bond between steel and metallic zinc is obtained by immersing the steel in a zinc bath at a temperature of around 460°C. Although the hot-dip galvanizing procedure is recognized to be one of the most effective techniques to combat corrosion, cracks can arise in the intermetallic δ layer. These cracks can affect the life of the coated material and decrease the lifetime service of the entire structure. In the present paper the mechanic...

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Weight minimization of truss structures with Big Bang-Big Crunch

The Big Bang  Big Crunch (BB BC) optimization method is a recently developed meta-heuristic alg... more The Big Bang  Big Crunch (BB BC) optimization method is a recently developed meta-heuristic algorithm that mimics the process of evolution of the universe. BB BC has been proven very efficient in design optimization of skeletal structures but yet computationally more expensive than classical meta-heuristic algorithms such as genetic algorithms and simulated annealing. To overcome this limitation, the paper presents a novel hybrid formulation of BB BC where the meta-heuristic search is hybridized by including gradient/pseudo-gradient information as a criterion to perform new explosions. Each new trial design is formed by combining a set of descent directions and eventually corrected in order to improve it further. The new BB BC algorithm is successfully tested in two classical weight minimization problems of a spatial 25-bar truss and a planar 200-bar truss.

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Numerical and experimental optimization of a critical part of a parking brake

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Non-uniform residual stress fields on sintered materials

The hole-drilling method (HDM) is a convenient and effective method for measuring residual stress... more The hole-drilling method (HDM) is a convenient and effective method for measuring residual stresses near the surface of an isotropic linear-elastic material. The measurement procedure is relatively simple, and has been standardized in ASTM Standard Test Method E837. The HDM is also versatile and can be performed in laboratory or in situ, on components ranging widely in size and shape. It is often referred to as a “semidestructive” technique, since the small hole will not, in many cases, significantly impair the structural integrity of the part being tested. The basic principle was first introduced by Mathar in 1934. Since that time, many researchers have further developed the method, culminating in the establishment of a standardized procedure ASTM E837. At least three established methods are available for estimating non-uniform residual stress fields from relaxed strain data from the incremental HDM. They are the Power Series, the Integral and the ASTM E837-08 Methods. These methods rely on finite element calculated calibration data, utilize different approaches for stabilizing and smoothing the non uniform residual stress field, and do not have the theoretical shortcomings of the two traditional methods (the Incremental Strain and the Average Strain Methods). Since the strain variations during drill depends on many factors hardly predictable and checkable a priori, it seems that the best calculation method should be evaluated for each particular experiment. This paper compares the Power Series, Integral and ASTM E837-08 methods as procedures for determining non-uniform residual stress fields using strain relaxation data from the HDM. Specimens made of AISI Maraging 300 steel by means of Selective Laser Melting are investigated and the residual stress profiles performed by means of all three stress calculation procedures are also presented and compared.

Discussion On The Thermal Field Produced By Laser Annealing For The Residual Stress Relaxation

Considerations On The Choice Of The Drilled Hole Diameter In ESPI-HDM Residual Stress Measurements In Ti6Al4V

During the years the Hole Drilling Method (HDM), that is the most common approach to measure resi... more During the years the Hole Drilling Method (HDM), that is the most common approach to measure residual stresses in components, has grown up in equipment sophistication. Nowadays, in fact, full field optical techniques are becoming increasingly adopted in replacing strain gage transducers. Their advantages consist in providing higher sensitivity and avoiding the long and expensive step of transducers application. The hole diameter represents one of the several parameters involved in the drilling process, its extension affects the entity of strain relieved. Drilling a hole with a bigger diameter allows to obtain higher strain that are, as a consequence, easier to detect and to measure. On the contrary, a hole with a small diameter should be preferred in view of the subsequent repairing process. Furthermore, being the analysis area related to the area of the hole, using higher diameter of the drill bit could compromise the analysis itself due to the limited area around the hole, particu...

Structural response of polyethylene foam-Based sandwich panels subjected to edgewise compression

This study analyzes the mechanical behavior of low density polyethylene foam core sandwich panels... more This study analyzes the mechanical behavior of low density polyethylene foam core sandwich panels subjected to edgewise compression. In order to monitor panel response to buckling, strains generated in the facesheets and overall out-of-plane deformations are measured with strain gages and projection moiré, respectively. A finite element (FE) model simulating the experimental test is developed. Numerical results are compared with moiré measurements. After having been validated against experimental evidence, the FE model is parameterized, and a trade study is carried out to investigate to what extent the structural response of the panel depends on the sandwich wall construction and facesheet/core interface defects. The projection moiré setup utilized in this research is able to capture the sudden and very localized buckling phenomena occurring under edgewise compression of foam-based sandwich panels. Results of parametric FE analyses indicate that, if the total thickness of the sandwich wall is fixed, including thicker facesheets in the laminate yields a larger deflection of the panel that becomes more sensitive to buckling. Furthermore, the mechanical response of the foam sandwich panel is found to be rather insensitive to the level of waviness of core-facesheet interfaces.

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Calibration of barkhausen noise for residual stress measurement

Industry has been searching for ways to measure residual stresses accurately, quickly and easily ... more Industry has been searching for ways to measure residual stresses accurately, quickly and easily without damage to the material being tested. Several methods have been developed; however, these are either destructive or of limited capability. A less conventional approach, the magnetic Barkhausen noise (MBN) method, is of particular interest because of its potential as a non-destructive industrial tool to measure residual stress and other microstructural parameters. The purpose of this study is evaluation of the relation between residual stress and magnetic Barkhausen noise in Fe360 Steel specimens. A MBN-stress calibration set-up was developed. To control the accuracy and the effectiveness of the developed system and procedure, various MBN measurements were carried out; hardness measurements were also conducted.

Drilling speed effects on accuracy of HD residual stress measurements

ABSTRACT The effect, on the residual stress measurement accuracy, of the drilling speed of the en... more ABSTRACT The effect, on the residual stress measurement accuracy, of the drilling speed of the end-mill during the hole-drilling measurements was evaluated in Ti6A14V. In spite of the well-known consideration that the highest achievable speed should be used during hole drilling, very few experimental works exist analyzing the effects of using lower velocities. Hole-drilling experiments were performed in this study by measuring the released strain by electronic speckle pattern interferometry. A known stress state was generated by loading the sample in a four point bending frame up to 50% of the yield strength. Drilling speed ranging in 5,000 ÷ 50,000 rpm was investigated by using an electronically controlled mill. The expected stress field, evaluated by a numerical model in ANSYS®, was compared with the measured one at different drilling speeds.

Acoustic emission analysis of aluminum specimen subjected to laser annealing

ABSTRACT This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen... more ABSTRACT This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during local annealing process by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a consequence of residual stress relieving. This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.

Effects of Strain’s Error on Residual Stresses Calculated by HDM

Conference Proceedings of the Society for Experimental Mechanics Series, 2012

The hole-drilling method is an effective and popular semi-destructive technique for residual stre... more The hole-drilling method is an effective and popular semi-destructive technique for residual stress (RS) measurement. It consists in drilling a very small hole into the specimen. Consequently, RS relaxes in the hole and stresses in the surrounding region change causing strains also to change. A strain gage rosette, specifically designed and standardized measures these strains. Using stress–strain relationships, the RS field is calculated from the measured strains. In the case of not uniform RS, an incremental technique is used in which relieved strains are measured during a series of small hole depth increments. In contrast to the uniform stress case, not uniform stress calculations are extremely sensitive to errors in the measured strain: small strain measurement errors can cause significant variations in calculated stresses, particularly for stresses far from the surface.

Tensioni Residue in Componenti Sinterizzati

Sommario Il processo di Selective Laser Melting (SLM) è una delle tecnologie più interessanti tra... more Sommario Il processo di Selective Laser Melting (SLM) è una delle tecnologie più interessanti tra i processi di prototipazione rapida grazie alla possibilità di realizzare complessi manufatti 3D in metallo, con densità elevata e con proprietà meccaniche comparabili a quelle dei componenti prodotti con tecnologie convenzionali. Questo obiettivo può essere raggiunto utilizzando laser in grado di garantire elevati valori della densità di energia con basse velocità di scansione. Queste condizioni, unitamente ad una appropriata strategia di scansione, permettono la completa fusione delle particelle di polvere. Il meccanismo di fusione/solidificazione genera tensioni termiche residue altamente variabili nei pezzi prodotti con il processo SLM. Questo lavoro si propone di studiare la distribuzione di tensioni residue generate in componenti prodotti in acciaio 18 Ni Marage 300 al variare della strategia di scansione e dei principali parametri di processo. La misura delle tensioni residue vie...

Investigation on Fracture Behaviour of Turbine Blades Under Self‐Exciting Modes

Strain, 2008

: This paper investigates the failure mechanisms of turbine blades occurring during similar cond... more : This paper investigates the failure mechanisms of turbine blades occurring during similar conditions of turbine operation. Optical techniques are utilised to identify critical frequencies that may be the cause of blade fractures. For that purpose, time average, stroboscopic holographic interferometry and holographic moiré are utilised to record vibration patterns. Strain maps are computed from stroboscopic and holographic moiré patterns. Stress distributions are computed under the assumption of linear elasticity. It is found that stress trajectories deduced from holographic measurements match well with the initial trajectories of crack observed for the in‐service broken specimens. This fact allows the excitation modes causing blade fractures to be identified. Finite element analyses carried out on models corrected in view of the experimentally observed vibration modes provide the values of stress causing fracture initiation. The paper discusses the failure mechanisms of the blades on the basis the experimental evidence and finite elements results. The observed failure modes seem to be a form of the principal normal stress fracture criterion. An argument based on damage accumulation explains the observed behaviour. Further evidence on failure mechanisms is gathered from scanning electron microscope images of the fractured specimens.

Open hole compressive strength of composite laminates and sandwich panels: comparison between Budiansky–Fleck–Soutis model and experiments

Plastics, Rubber and Composites, 2012

ABSTRACT In this study, the compressive behaviour of carbon fibre reinforced plastic quasi-isotro... more ABSTRACT In this study, the compressive behaviour of carbon fibre reinforced plastic quasi-isotropic laminates and sandwich panels with carbon fibre reinforced plastic face sheets and syntactic foam core has been investigated. Experimentally determined open hole strengths have been compared with theoretical predictions obtained by applying a linear cohesive zone model. The unnotched compressive strength has been experimentally determined, and the in-plane fracture toughness has been analytically predicted as input parameters of the model. Buckling phenomena occurred on some specimens, and they have been taken into account. Evaluation of macroscopic failure modes in compression tests on unnotched specimens led to a better understanding on the advantages of the analytical model and on the possibility of applying the model to sandwich structures. The experimental results were in good agreement with the analytical prediction by the Budiansky–Soutis–Fleck cohesive zone model, and the difference between theoretical and experimental open hole strengths of Syncore sandwich panels was &lt;9%.

Experimental and numerical study of static and fatigue properties of titanium alloy welded joints

Mechanics of Materials, 2009

Titanium and its alloys have high specific strength, good mechanical properties at high temperatu... more Titanium and its alloys have high specific strength, good mechanical properties at high temperature, high resistance to corrosion and to attack by most acid solutions. Such characteristics make this material attractive for numerous applications because of recent improvements in welding techniques that allow to realize high quality welded joints. For example, new utilizations of titanium alloys are currently being studied

Effects of process parameters on the residual stresses measurements on titanium plates by using ESPI

Preparation of Explanted Coronary Stents for Investigation of Material Properties

Materials Today: Proceedings, 2016

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Caratterizzazione meccanica di nuovi materiali compositi “stitched/RFI

Residual Stress on Aisi 300 Sintered Materials

Conference Proceedings of the Society for Experimental Mechanics Series, 2011

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Residual Stress on Ti6Al4V Hybrid and Laser Welded Joints

Conference Proceedings of the Society for Experimental Mechanics Series, 2011

Characterization and Prediction of Cracks in Coated Materials: Direction and Length of Crack Propagation in Bimaterials

International Scholarly Research Notices, 2015

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Weight minimization of truss structures with Big Bang-Big Crunch

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Numerical and experimental optimization of a critical part of a parking brake

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Non-uniform residual stress fields on sintered materials

The hole-drilling method (HDM) is a convenient and effective method for measuring residual stress... more The hole-drilling method (HDM) is a convenient and effective method for measuring residual stresses near the surface of an isotropic linear-elastic material. The measurement procedure is relatively simple, and has been standardized in ASTM Standard Test Method E837. The HDM is also versatile and can be performed in laboratory or in situ, on components ranging widely in size and shape. It is often referred to as a “semidestructive” technique, since the small hole will not, in many cases, significantly impair the structural integrity of the part being tested. The basic principle was first introduced by Mathar in 1934. Since that time, many researchers have further developed the method, culminating in the establishment of a standardized procedure ASTM E837. At least three established methods are available for estimating non-uniform residual stress fields from relaxed strain data from the incremental HDM. They are the Power Series, the Integral and the ASTM E837-08 Methods. These methods rely on finite element calculated calibration data, utilize different approaches for stabilizing and smoothing the non uniform residual stress field, and do not have the theoretical shortcomings of the two traditional methods (the Incremental Strain and the Average Strain Methods). Since the strain variations during drill depends on many factors hardly predictable and checkable a priori, it seems that the best calculation method should be evaluated for each particular experiment. This paper compares the Power Series, Integral and ASTM E837-08 methods as procedures for determining non-uniform residual stress fields using strain relaxation data from the HDM. Specimens made of AISI Maraging 300 steel by means of Selective Laser Melting are investigated and the residual stress profiles performed by means of all three stress calculation procedures are also presented and compared.