Sandwich structures are employed in many different fields including automobile, marine, and aircraft structures. However, debonding may take place at the core-face sheet interface, reducing the stiffness of the structure. Debonding may occur for a variety of reasons, including initial manufacturing faults, changes in service loads, tool drops, and foreign object impacts. It is critical to comprehend how debonding zones impact the vibration of sandwich structures because decreases in the natural frequencies (NF) could lead to a structure vibrating at resonance and lead to structural failure. This paper investigates the influence of debonding shapes and debonding locations on the free-vibration behavior of sandwich structures. Different sandwich structures that have varied debonding shapes at various locations are modeled using COMSOL MULTIPHYSICS. Debonding is modeled by using the CZM model. Validation studies were performed to validate the current study. After the validation study, free vibration analysis of all the sandwich structures was performed and the first six NF were obtained from the simulations. The results show the influence of the debonding shapes and debonding locations on the NF of the sandwich structures. From the results, it was observed that both the debonding shapes and debonding locations significantly change the NF of the sandwich structures. The debonding shapes cause a reduction and an increase depending on the debonding location. It was also revealed that both debonding shapes and debonding locations have a significant effect on the vibration behavior of sandwich structures. Using this method, the debonding shape and location, delamination shape, and location can be predicted using machine learning algorithms. This study includes free vibration analysis of sandwich structures with different debonding shapes and locations, and the results show that natural frequencies change depending on the debonding shapes and locations. This information can be implemented in machine learning for use in the field of damage detection and utilized to predict the shape and location of delamination in sandwich structures.
Pod posadzką kościoła św. Elżbiety we Wrocławiu znajduje się pomieszczenie stanowiące zabezpieczony wykop archeologiczny. Powstało ono w końcu XX wieku w celu ekspozycji reliktów poprzedniego kościoła odkrytych w 1976 roku. Plany te nie zostały zrealizowane, a krypta nigdy nie pełniła funkcji ekspozycyjnej. Dla badań architektonicznych stanowi jednak kluczowy punkt kościoła. Położenie w jego centralnej części pozwalana dostęp do reliktów świątyni z XIII wieku oraz pozostałości po przebudowach kościoła w okresie średniowiecza i nowożytności – aż do końca XX wieku. Jako taka została w latach 2021–2022 zinwentaryzowana oraz przebadana metodą stratygraficzną. W efekcie powstało kompletne rozwarstwienie chronologiczne krypty. Wydzielono siedem faz budowlanych składających się na zapis całej historii kościoła. Umożliwiło to próbę rekonstrukcji dziejów kościoła późnoromańskiego oraz niektórych partii istniejącego.
EN
Underneath the floor of St. Elizabeth’s Church inWrocław is a room that is a secured archaeological excavation. It was created at the end of the twentieth century to display the relics of the former church discovered in1976. These plans were not implemented and the cryp twas never used as an exhibition space. For architectural research, however, it represents a key point in the church. Its location in its central part allows access to the relics of the thirteenth-century church, as well as there mains of the church’s alterations in the medieval and early modern periods—up to the end of the twentieth century. As such, it was inventoried in 2021–2022 and surveyed using the stratigraphic method. The result was a complete chronological stratification of the crypt. Seven construction phases were separated, making up the record of the entire history of the church. This enabled an attempt to reconstruct the history of the late Romanesque church and some parts of the existing one.
W artykule przedstawiono badania rozwarstwienia prefabrykowanych sprężonych belek betonowych. Głównym celem programu badań jest określenie wpływu kształtu zespolenia na zachowanie się belek zespolonych. Zbadano żebrowe prefabrykowane belki sprężone z pełnym zespoleniem, zerwaną adhezją i zerwaną adhezją oraz tarciem. Pomiary z wykorzystaniem technologii cyfrowej korelacji obrazu (DIC) wraz z analizą charakterystyki siła-przemieszczenie wykazały decydujący wpływ długości rozwarstwienia na pracę elementu. Powstawanie lokalnego poślizgu w płaszczyźnie zespolenia związane było z propagacją zarysowań giętnych i ukośnych. Zarysowanie dochodzące do strefy podparcia należy uznać za moment rozwarstwienia elementu zespolonego.
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The article presents a study of the interface behavior of precast pre-stressed composite beams. The main objective of the research program is to determine the influence of the interface’s shape on the composite element’s behavior. The rib-shaped precast prestressed beams with full bond, broken adhesion and broken contact were tested. DIC measurements with force-displacement relations analysis showed a crucial impact of cracking length on element performance. The formation of the local slip of the interface was related to the propagation of flexural and shear cracks. The crack reaching the support zone should be considered the moment of debonding of the composite element.
Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's ModeI fracture toughness test findings. The MBT technique's 𝐺Ic values for initiation and propagation are 0.533 and 0.679 KJ/m2 , respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the 𝐺IIc values for the CBBM technique are 1.65 KJ/m2 for non-pre cracked and 1.4 KJ/m2 for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness.
The article aims at assessing the influence of the drill bit material on the bearing strength of holes made in glass fabric reinforced epoxy composite. Six twists made of widely used drill materials such as high speed steels and carbides in different configurations were selected to drill holes in the composite. In the first stage of the work, optimum drilling parameters were selected and then used for drilling holes in specimens tested in single lap shear experiments. For each tested specimen two different delamination factors, one based on the delamination area and another - on its diameter, were calculated in order to assess the quality of the holes and then compared to the results of the bearing strength experiments. The results of the bearing tests showed that the highest strength was achieved for the high speed steel drill with titanium coating while the lowest for the cemented carbide drill. This finding is in opposition to the majority of results reported in literature.
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Celem artykułu jest przedstawienie problemów jakościowych, jakie występują podczas procesu tłoczenia, a związane są one z wadami i defektami materiału. Już w trakcie wcześniejszych operacji produkcyjnych i technologicznych może dojść do problemów, które mają wpływ na jakość wytwarzanej blachy.
Purpose: Present paper addresses the formulation of delamination-fretting wear failure predictive equation in HAp-Ti-6Al-4V interface of hip arthroplasty femoral stem component using multiple linear regression model. Design/methodology/approach: A finite element computational model utilising adaptive meshing algorithm via ABAQUS/Standard user subroutine UMESHMOTION is developed. The developed FE model is employed to examine effect of different HAp-Ti-6Al-4V interface mechanical and tribological properties on delamination-fretting wear behaviour. The FE result is utilised to formulate predictive equations for different stress ratio conditions using multiple linear regression analysis. Findings: Delamination-fretting wear predictive equations are successfully formulated with significant goodness of fit and reliability as a fast failure prediction tool in HAp coated hip arthroplasty. The robustness of predictive equations is validated as good agreement is noted with actual delamination-fretting wear results. Research limitations/implications: The influence of different mechanical and tribological properties such as delamination length, normal loading, fatigue loading, bone elastic modulus and cycle number under different stress ratio on delamination-fretting wear failure is analysed to formulate failure predictive equations. Practical implications: The formulated predictive equation can serve as a fast delamination-fretting wear failure prediction tool in hip arthroplasty femoral stem component. Originality/value: Limited attempt is done to explore the potential of utilizing multiple linear regression model to predict failures in hip arthroplasty. Thus, present study attempt to formulate delamination-fretting wear failure predictive equation in HAp -Ti-6Al-4V interface of hip arthroplasty femoral stem component using multiple linear regression model.
In recent years, manufacturing industries have demanded high-performance materials for structural components development due to their reduced weight, improved strength, corrosion, and moisture resistance. The outstanding performance of polymer nano-composites substitutes the use of conventional composites materials. This study is concerned with the machining of MWCNT and glass fiber-modified epoxy com posites prepared by a cost-effective hand layup procedure. The investigations were carried out to estimate the generation of the thrust force (Th) and delamination factors at entry (DFentry) and exit (DFexit) side during the drilling of fiber composites. The effect of varying constraints on the machining indices was explored for obtaining an adequate quality of hole created in the epoxy nano-composites. The outcome shows that the feed rate (F) is the most critical factor influencing delamination at both entry and exit side, and the second one is the thrust force followed by wt.% of MWCNT. The statistical study shows that optimal combination of S (1650 Level-2), F (165 Level-2), and 2 wt.% of MWCNT (Level-2) can be used to minimize DFentry, DFexit, and Th. The drilling-induced damages were studied by means of a high-resolution microscopy test. The results reveal that the supplement of MWCNT substantially increases the machining efficiency of the developed nano-composites.
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The work present the coupled circuit method applied to an eddy current nondestructive testing (EC-NDT) problems. The device is consisting on a conductive multilayer structure having an air gap (delamination), or a physical defect (lack of material). The purpose of the study is to identify the presence of the delamination when a physical defect can occur simultaneously. The use of Coupled Circuits Method permits to reduce the discretization to only the active parts without mesh air gap. The results obtained are compared to finite elements ones. A good agreement is observed between results. Interesting and useful conclusions are made.
PL
W pracy przedstawiono metodę obwodów sprzężonych zastosowaną do badań nieniszczących prądów wirowych (EC-NDT). Urządzenie składa się z przewodzącej konstrukcji ze szczeliną powietrzną (rozwarstwieniem) lub wadą fizyczną (brak materiału). Celem badania jest identyfikacja obecności rozwarstwienia, gdy jednocześnie może wystąpić wada fizyczna. Zastosowanie metody obwodów sprzężonych pozwala zredukować dyskretyzację tylko do aktywnych części bez siatkowej szczeliny powietrznej. Uzyskane wyniki porównuje się z wynikami elementów skończonych. Obserwuje się dobrą zgodność wyników.
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Layer composites reinforced with fabrics – laminates are construction materials in which mechanical properties can be shaped by designing their microstructure appropriately. However, the multi-phase microstructure of laminates makes it difficult to calculate the strength of the laminate constructions, especially when the reinforcement is a fabric. The article presents a special calculation model for determining the strength of an exemplary construction element made of laminate reinforced with a roving fabric with a plain weave made of carbon fibers. The computational model reflected in a simplified way the laminate microstructure, i.e. the number and orientation of the reinforcement fabric layers and its weave, and enabled a simulation of the behavior of the construction element under load up to fracture, which occurred as a result of breaking the reinforcement and interlayer crack – delamination. The simulation results were compared with the results of experimental stand tests. A method of modifying the computational model for laminates reinforced with non-plain weave was also suggested.
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Layered metallic materials (LMMs) offer superior properties in comparison to their counterpart monolithic sheets. Single-point incremental forming (SPIF) has emerged as an economical solution to produce LMM parts. However, delamination can limit the formability of such parts. In this study, the delamination analysis during SPIF of layered sheets was performed. Steel/steel bi-layer sheets were fabricated by roll bonding. These sheets were produced at thickness reduction ratios of 47%, 58% and 70%. The bond strength and fracture toughness in mode I and mode II were determined by T-peel and tensile shear tests, respectively. When the thickness reduction ratio was increased from 47 to 70%, an increase in bond strength was observed with 572% increase in mode I and 15.6% in mode II, respectively. On the other hand, with the same percent increase in thickness reduction, the critical strain energy release showed an increase of 3992% in mode I and 20% decrease in mode II. Surface-based cohesive zone model was used to define the interface between layers during numerical simulation of SPIF for delamination analysis. To validate the numerical results, SPIF of given bi-layer sheet was performed experimentally and a good agreement between the numerical and experimental results was observed.
Laminated Aluminum Composite Structure (LACS) has shown great potential for replacing traditional bulk aluminum parts, due to its ability to maintain low manufacturing costs and create complex geometries. In this study, a LACS, that consists of 20 aluminum layers joined by a structural tape adhesive, was fabricated and tested to understand its impact performance. Three impact tests were conducted: axial drop, normal and transverse three-point bending drop tests. Numerical simulations were performed to predict the peak loads and failure modes during impacts. Material models with failure properties were used to simulate the cohesive failure, interfacial failure, and aluminum fracture. Various failure modes were observed experimentally (large plastic deformation, axial buckling, local wrinkling, aluminum fracture and delamination) and captured by simulations. Cross-section size of the axial drop model was varied to understand the LACS buckling direction and force response. For threepoint bending drop simulations, the mechanism causing the maximum plastic strain at various locations in the aluminum and adhesive layers was discussed. This study presents an insight to understand the axial and flexural responses under dynamic loading, and the failure modes in LACS. The developed simulation methodology can be used to predict the performance of LACS with more complex geometries.
The aim of the presented work is to determine (i) mechanical properties of the ascending aorta wall (DAA) and the wall of the ascending aortic aneurysm (DAAA), in which spontaneous dissection resulting from the evolving disease occurred, and (ii) the strength of the interface between the layers in the above-mentioned vessels. Methods: The mechanical tests were divided into two steps. In the first step the mechanical properties of the of DAA and DAAA walls were examined on the basis of uniaxial stretching until rapture. In the next step the mechanical parameters of the interface between layers of DAA and DAAA walls were determined by the peeling test. Results: Higher values of tensile strength (max) and Young’s modulus (E) were obtained for the DAAA group, to which the dissecting wall of the ascending aortic aneurysm was classified. For circumferential samples, the difference between the DAAA and DAA groups was 39% in the case of tensile strength and 70% in the case of the Young’s modulus. Conclusions: Summarizing, the studies performed showed that the dissection process is different in the case of the ascending aortic aneurysm wall and the ascending aorta wall. The wall of the ascending aortic aneurysm is more susceptible to dissection, as evidenced by lower values of the mechanical parameters of the interface between the intima and the media-adventitia complex. The obtained results of mechanical properties tests confirm that dissection and aneurysm should be treated as separate disease entities that may coexist with each other.
The paper deals with numerical modeling of delamination of laminate plate consists of unidirectional fiber reinforced layers. The methodology adopts the first-order shear laminate plate theory and fracture and contact mechanics. There are described sublaminate modeling and delamination modeling by the help of finite element analysis. With the interface modeling there is calculated the energy release rate along the lamination front. Analytical expressions for total energy release rate and its mode components are given in terms of interface variables and plate stress resultant discontinuities. Numerical results are given for mixed mode delamination problems by implementing the method in a 2D finite analysis, which utilizes shear deformable plate elements and interface elements. Numerical example is done by the commercial ANSYS code.
PL
Artykuł dotyczy numerycznego modelowania rozwarstwienia płyty laminowanej składającej się z warstw zbrojonych jednokierunkowo włóknami. W metodologii przyjęto teorię płyty laminowanejna ścinanie pierwszego rzędu oraz mechanikę pękania i kontaktu. Opisano modelowanie sublaminatowe i modelowanie delaminacji za pomocą analizy elementów skończonych. Przy modelowaniu interfejsu obliczono szybkość uwalniania energii wzdłuż czoła laminatu. Wyrażenia analityczne dla całkowitej szybkości uwalniania energii i jej składników modalnych podano w odniesieniu do zmiennych interfejsowych i wynikających z nich nieciągłości naprężeń płyt. Wyniki liczbowe podano dla problemów delaminacji w trybie mieszanym poprzez zastosowanie metody w dwuwymiarowej skończonej analizie, która wykorzystuje odkształcalne na ścinanie elementy płytowe i elementy interfejsu. Przykład numeryczny obliczono z wykorzystaniem programu ANSYS.
W artykule przedstawiono wyniki rozwoju rozwarstwień skał wokół wyrobiska przygotowawczego w KWK „Dobropolskaja” na Ukrainie. Konstrukcję stacji pomiarowych wykonano zgodnie z metodą WNIMI (Wszechzwiązkowy Instytut Miernictwa Naukowo- Badawczy). Stacje pomiarowe były wyposażone w rozwarstwieniomierze, które zainstalowano bezpośrednio w przodku chodnika. Analizę dynamiki rozwoju strefy rozwarstwienia skał stropu wyrobiska sporządzono na podstawie wyników przemieszczeń rozwarstwieniomierzy wielopunktowych. W podsumowaniu podano czas, dla którego w górotworze skalnym zaczynają pojawiać się deformacje, których dalszy rozwój może doprowadzić do obwałów stropu powyżej strefy skotwionej. Stwierdzono, że dla warunków górniczo-geologicznych poziomu 450, zakotwiony strop przemieszcza się bez znacznych rozwarstwień na głębokości od konturu 1,0 ÷ 2,3 m, a odcinek stropu na głębokości między 0,5 ÷ 1,0 m odspaja się od wyżej leżącej części.
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This paper presents the results of development of delaminations of rocks around preparatory gateroad in hard coal mine „Dobropolskaja” in Ukraine. The construction of measuring stations were carried out in accordance with the method of the Institute of Metrology WNIMI (All-union Metrology Institute for Scientific Research). Measuring stations were equipped with deep datum points, installed directly in the forehead of gateroad. In order to analyze the dynamics of the development of zone around the damaged rock excavation, deformation graphs of rocks depending on the distance from the contour of the excavation on the basis of deep datum points movements were prepared. In conclusion, the period of time for which the rock mass began to demonstrate deformation, which can later lead to roof falls outside the protected area through bolt support, was given. It was found that for the geological – mining conditions on the 450 level, the bolted roof is moved without any significant delamination at a depth of 1,0 ÷ 2,3 m, and a section of roof at a depth of between 0.5 ÷ 1.0 m is loosening from the above-lying parts.
W artykule przedstawiono wyniki badań dołowych parametrów geomechanicznych górotworu oraz jakości obudowy betonowej wyrobisk w otoczeniu georeaktora podziemnego zgazowania węgla. Badania te obejmowały pomiary: parametrów mechanicznych węgla i skał, rozwarstwienia skał oraz wytrzymałości i struktury obudowy. W badaniach wykorzystano penetrometr hydrauliczny, kamerę otworową, młotek Schmidta, metodę pull-out, rozwarstwieniomierz oraz georadar. Badania te przeprowadzone zostały w trakcie prowadzenia eksperymentu Podziemnego Zgazowania Węgla (PZW) w Kopalni Doświadczalnej (KD) „Barbara".
EN
This paper presents the results of underground investigation aiming at the assessment of influence of underground coal gasification on geomechanical parameters of rock mass and quality of concrete support in the surroundings of a geaoreactor. The investigation comprises assessment of geomechanical parameters of coal, floor and roof strata, roof displacements and concrete support strength parameters. Hydraulic penetrometer, endoscopic camera, Schmidt hammer, pull-out method, telltale and GPR (ground penetration radar) were used during measurements. The investigations were carried out during the UCG process conducted in the Experimental Mine "Barbara".
Przeglądowy artykuł zawiera stan wiedzy dotyczący modelowania delaminacji z wykorzystaniem elementów kohezyjnych w kompozytach o spoiwie polimerowym, dostępnych w komercyjnym oprogramowaniu MES (np. w programie Abaąus). W artykule opisano działanie elementów kohezyjnych w warunkach pojedynczego i mieszanego sposobu pękania elementów o charakterystyce biliniowej. Elementy kohezyjne mogą przyjmować różne charakterystyki. W artykule zostały opisane różnice w wynikach uzyskanych z wykorzystaniem różnych charakterystyk. Opisane zostały również stałe materiałowe wymagane do definicji modelu. Wyznaczenie wartości tych stałych metodą eksperymentalną jest trudne do zrealizowania. W artykule przybliżono metody eksperymentalne oraz opisano kalibrację modelu pozwalającą na oszacowanie stałych, bazując na znormalizowanych badaniach. Artykuł ma na celu wyjaśnić sposób działania elementów kohezyjnych w komercyjnych programach MES i wskazać trudności związane z ich wykorzystywaniem.
EN
This review article contain description of cohesive zone modeling before delamination front in composite materials with polymer matrix. For this purpose the cohesive elements are proposed. Work of these elements were characterized in pure and mix mode loading. Different shapes of cohesive law, their parameters and influence on performing calculation and results were described. The aimi of this article is to shortly explains work of cohesive elements which are implemented in commercial FEM programs but they are not enough described in manuals and brings closer problems which could be encountered.
The paper presents a non-destructive diagnostic technique based on guided wave propagation phenomenon used to assess the adhesive bonding between a steel bar and a concrete cover. Double-layered cylindrical specimens with different levels of debonding and its location were investigated. The influence of bonding length on the excitation of multiple modes of longitudinal guided waves was analysed. Numerical simulations of guided wave propagation in healthy and damaged specimens were conducted and differences in the occurring phenomena were specified. The analysis of the obtained results confirms the possibility to apply the guided wave propagation method in the assessment of degradation level in the adhesive bonding of multi-layered cylindrical structures.
PL
W artykule przedstawiono nieinwazyjną technikę diagnostyczną wykorzystującą zjawisko propagacji fal prowadzonych w ocenie stanu połączenia adhezyjnego pomiędzy stalowym zbrojeniem a otuliną betonową. Przeanalizowano dwuwarstwowe próbki cylindryczne z różnymi wielkościami i położeniami delaminacji między warstwami. Opisano także wpływ długości zakotwienia na wzbudzenie kolejnych modów podłużnych fal prowadzonych. Symulacje numeryczne propagacji fal zostały przeprowadzone dla prętów stalowych osadzonych w betonie w stanie bez uszkodzenia oraz z uszkodzeniem w postaci braku przyczepności między stalą a betonem. Wskazano na różnice w zachodzących zjawiskach propagacji fali w zależności od stopnia rozwarstwienia. Analiza uzyskanych rezultatów potwierdza możliwość wykorzystania zjawiska propagacji fal w ocenie stopnia degradacji połączeń adhezyjnych wielowarstwowych konstrukcji cylindrycznych.
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Finite element simulation was carried out to better understand damage formation in CF/epoxy plate in the course of a low velocity 8J impact. The plate under investigation was of [+30/−30]s lay-up. To validate the numerical results a drop test was carried out with the help of a drop tower. The interlaminar damage extent was determined with the help of C-scan. Comparison between the numerical and experimental results showed a good quantitative agreement concerning contact force time history, however, the amount of dissipated energy determined based on the numerical simulation was lower than that from the experiment,consistently, the damage extent determined based on numerical simulation was smaller than that determined by C-scan. Nevertheless, characteristic points on the plot representing contact force time history could be related to the particular damage mechanism onsets and their actions.
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