T Matikas | University of Ioannina/Greece (original) (raw)

Papers by T Matikas

Mechanical Behavior of Advanced Materials

The transverse tensile strength of the fiber-matrix interface plays an important role in controll... more The transverse tensile strength of the fiber-matrix interface plays an important role in controlling a number of failure modes in polymer matrix composites (PMCs). These include the transverse failure of 90° plies, as well edge delamination in PMC laminates. On the other hand, while significant attention has been focused in the PMC literature on interface shear failure, such as under pull-out conditions, little attention has been focused on the interface tensile strength. In order to avoid edge effects, a cruciform geometry was selected for evaluating the tensile strength. SiC fibers with different types of coatings were evaluated inside an epoxy matrix, and the bond strength was estimated from the mechanical test data. Interface failure was confirmed using optical, dye penetrant, and an ultrasonic shear wave back reflection technique. Tests using straight sided specimens confirmed that singularities at specimen edges have significant influence on interface failure, and hence must b...

Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduct... more Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The properties of advanced composites rely on the quality of the fiber-matrix bonding. Service-induced damage results in deterioration of bonding quality, seriously compromising the load-bearing capacity of the structure. While traditional methods to assess bonding are destructive, herein a nondestructive methodology based on shear wave reflection is numerically investigated. Reflection relies on the bonding quality and results in discernable changes in the received waveform. The key element is the “interphase ” model material with varying stiffness. The study is an example of how computational methods enhance the understanding of delicate features concerning the nondestructive evaluation of materials used in advanced structures. 1.

The non-destructive monitoring of the damage evolution in carbon fiber reinforced polymers (CFRPs... more The non-destructive monitoring of the damage evolution in carbon fiber reinforced polymers (CFRPs) during mechanical loading is a key issue in many applications, especially in aerospace structures. Recent studies have shown that the mechanical deformation and the electric resistance of CFRPs are closely connected, and, as a result, the material can inherently

Components in rotational machinery such as turbine blades used in military aircraft engines are s... more Components in rotational machinery such as turbine blades used in military aircraft engines are subjected to low-amplitude, high-frequency loads in the kHz range. Under high cycle fatigue (HCF), the initiation state of a crack consumes most of the life of the component. Vibratory stresses may therefore result in unexpected failures of the material. Hence, there is a need for HCF studies to address HCF-related failures of turbine engines and to develop a life prediction methodology. Ultrasonic fatigue provides accelerated HCF testing enabling the simulation of realistic loading conditions for testing materials used in structural components subjected to vibratory stresses. Specimen design is critical for optimum ultrasonic fatigue testing. The objective of this study is therefore to develop analytical modelling necessary for the design of test coupons to be fatigue tested at ultrasonic frequencies.

In the current study, a research was conducted in three different steel categories of high and me... more In the current study, a research was conducted in three different steel categories of high and medium ductility such as B400c, B450c and B500b under seismic loads which were simulated with low cycle fatigue tests. Based on the results of mechanical tests, SEM and EDX on the above steel specimens before and after accelerated corrosion it is important to mention the negative role of sulfides, as it is mainly MnS inclusions, with existence of chloride ions and buckling phenomena in Structural Integrity of rebars.

ANNOTATION Internal damage accumulation of Ti-6Al-4 V specimens subjected to controlled levels of... more ANNOTATION Internal damage accumulation of Ti-6Al-4 V specimens subjected to controlled levels of low cycle fatigue (LCF) and high cycle fatigue (HCF) is being studied. The material was processed into a forged plate with a duplex microstructure representing engine components. The purpose of the controlled-damage samples is to create calibration standards for damage characterization and quantification for the novel nondestructive technique of nonlinear acoustics (NLA). Nonlinear acoustics provides real-time, in-situ monitoring of internal damage during mechanical· testing. The knowledge gained from transmission electron microscopy (TEM) is being used to develop a new characterization method for fatigue damage accumulation by the NLA technique in the crack precursor stage, which is prior to c~ack nucleation. The desired outcome is a methodology to predict the remaining life in fatigue loaded samples using the nondestructive, nonlinear acoustic technology.

$Research paper thumbnail of AE monitoring of the fracture behavior of mortar specimens modified with waterproofing adhesives$

Nowadays, the use of adhesives in building materials for enhancing the mechanical properties and ... more Nowadays, the use of adhesives in building materials for enhancing the mechanical properties and the final performance at the maximum level is standard practice. Moreover, the interest of the construction industry for extensively testing the effectiveness of the new modified products is increased. This study aims to examine the fracture behavior of mortar specimens modified with waterproofing adhesives using acoustic emission (AE). For the mortar beams' production, the portion of active mix water has been changed with the use of different kinds of emulsion resins for investigating the waterproofing mechanism at final usage. For this, the slurries that have been examined are commonly used at the construction of swimming pools. The specimens were tested in three-point bending and compression. The ultrasonic velocity of the samples was also determined. The results indicate that the use of adhesives in mortars can be successfully characterized by AE and ultrasonic parameters, making...

The demands for constructions with high mechanical performance, located in seismic areas, express... more The demands for constructions with high mechanical performance, located in seismic areas, expressed through EC2 and EC8part3, were importantly satisfied mainly with the use of Tempcore dual phase steel bars. High mechanical performance of dual phase steel comes from the combination of the mechanical properties of each individual phase. However, several times have been reported problems concerning their structural cohesion. In the present study four different technical classes (DP) of reinforcing steel bars were used: B500c, B450c, B400c and B500b. SEM and EDX analyses were used, focusing not only on the internal defects regions of the materials (before and after corrosion), but also on the external areas affected by pitting corrosion. Moreover, in terms of the experimental procedure, mechanical tensile tests were conducted, on both corroded and non corroded reinforcing steel bar specimens and the pertinent results are analyzed. The conclusion from the present study is that both inte...

Procedia Structural Integrity

Thermosense: Thermal Infrared Applications XXXVIII

In this work the influence of the microstructure at the vicinity of the interface on the fracture... more In this work the influence of the microstructure at the vicinity of the interface on the fracture behavior of particulate-reinforced aluminum alloy matrix composites (Al/SiCp composites) is studied by using thermographic tools. In particular, infrared thermography was used to monitor the plane crack propagation behavior of the materials. The deformation of solid materials is almost always accompanied by heat release. When the material becomes deformed or is damaged and fractured, a part of the energy necessary to initiate and propagate the damage is transformed in an irreversible way into heat. The thermal camera detects the heat wave, generated by the thermo-mechanical coupling and the intrinsic dissipated energy during mechanical loading of the sample. By using an adapted detector, thermography records the two dimensional "temperature" field as it results from the infrared radiation emitted by the object. The principal advantage of infrared thermography is its noncontact, non-destructive character. This methodology is being applied to characterise the fracture behavior of the particulate composites. Infrared thermography is being used to monitor the plane crack propagation behavior of such materials. Furthermore, an innovative approach to use microscopic measurements using IR microscopic lenses was attempted, in order to enable smaller features (in the micro scale) to be imaged with accuracy and assurance.

Journal of Applied Mechanical Engineering

In this study the influence of corrosion and seismic load (low-cycle fatigue LCF) in the mechanic... more In this study the influence of corrosion and seismic load (low-cycle fatigue LCF) in the mechanical performance of reinforcing steel bars of S400 grade with 10 mm nominal diameter was investigated. There took place 140 tensile, LCF and salt spray tests which performed on reinforcing bars in different conditions. The results show that the corrosion level and surface conditions are the main parameters which affect to the low-cycle fatigue life of reinforcing bars. Moreover, through a non-linear regression analysis of the experimental data, a model of predicting the expectancy life of the corroded rebars was conducted. This prediction was based on two models: the first model was about an imposed of (total) strain amplitudes (ε α) and the second model on predicting the strength degradation per cycle of fatigue in correlation with the plastic strain amplitudes (ε p). Both the experimental study and the prediction modeling conducted for the same steel grade S400 with and without ribs. The model prediction of non-linear regression analysis, show a good agreement with the observed experimental results and adequately confirmed the experimental results showing that from the first levels of corrosion, the degradation of their life expectancy was obvious as well the rebars without ribs (smoothed) which present more advanced mechanical behavior and life expectancy against to the respective ribbed rebars.

Plastics, Rubber and Composites, 2016

The scope of this study is the real-time monitoring and evaluation of the healing process using n... more The scope of this study is the real-time monitoring and evaluation of the healing process using novel testing procedures and non-destructive evaluation techniques. In this work, the healing approach that has been followed is that of the intrinsic Diels–Alder (DA) and retro-DA mechanism. Two polymers were used as adhesives in single lap-joint specimens that were subjected to static tensile loading. The healed specimens were subjected to the same testing procedure as the one before the first failure and the healing efficiency was assessed by the correlation of the experimental results prior and after healing. Acoustic emission and infrared thermography were employed with the destructive tests so as to monitor changes in the acoustic and the thermal profile between the virgin and the ‘healed’ specimen.

Smart Materials and Nondestructive Evaluation for Energy Systems 2016, 2016

The corrosion behavior of metallic structures is an important factor of material performance. In ... more The corrosion behavior of metallic structures is an important factor of material performance. In case of aluminum matrix composites corrosion occurs via electrochemical reactions at the interface between the metallic matrix and the reinforcement. The corrosion rate is determined by equilibrium between two opposing electrochemical reactions, the anodic and the cathodic. When these two reactions are in equilibrium, the flow of electrons from each reaction type is balanced, and no net electron flow occurs. In the present study, aluminum alloy tensile-shape samples are immersed in NaCl solution with an objective to study the effect of the controlled pitting corrosion in a specific area. The rest of the material is completely sealed. In order to investigate the effect of pitting corrosion on the material performance, the specimens were subjected to cyclic loading. The effect of corrosion on the fatigue life was assessed using two complimentary nondestructive methods, infrared thermography and acoustic emission.

Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, and Civil Infrastructure 2016, 2016

This paper deals with the use of complimentary nondestructive methods for the evaluation of damag... more This paper deals with the use of complimentary nondestructive methods for the evaluation of damage in engineering materials. The application of digital image correlation (DIC) to engineering materials is a useful tool for accurate, noncontact strain measurement. DIC is a 2D, full-field optical analysis technique based on gray-value digital images to measure deformation, vibration and strain a vast variety of materials. In addition, this technique can be applied from very small to large testing areas and can be used for various tests such as tensile, torsion and bending under static or dynamic loading. In this study, DIC results are benchmarked with other nondestructive techniques such as acoustic emission for damage localization and fracture mode evaluation, and IR thermography for stress field visualization and assessment. The combined use of these three nondestructive methods enables the characterization and classification of damage in materials and structures.

Proceedings of the 6th International Conference on Emerging Technologies in Non-Destructive Testing (Brussels, Belgium, 27-29 May 2015), 2015

Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2009, 2009

Surface deterioration is the most common type of concrete damage. In the case of subsurface damag... more Surface deterioration is the most common type of concrete damage. In the case of subsurface damage the difficulty of characterization increases as there is no visual evidence of the crack. Additionally since the close to surface layer of the material is intact, the sensitivity of the longitudinal wave velocity, which is typically measured for inspection purposes, is questionable. In the

Advanced Topics in Scattering Theory and Biomedical Engineering, 2010