Hans Jelitto

Technische Universität Hamburg | TUHH · Institute of Advanced Ceramics

A planetary correlation with the planets of our solar system has been found for the pyramids of Giza and now also for the pyramids at Teotihuacán in Mexico. This is a revised and extended version of the P4 Program Description from June, 2015. Concerning Giza, the extension relates mainly to the comparison between the planetary constellations and th...

A planetary correlation has been detected concerning the pyramid area at Teotihuacán, Mexico. The central Avenue of the Dead seems to represent a logarithmic astronomical scale and the pyramids, the temple of Quetzalcoatl, the solid barriers on the avenue and the Rio San Juan define markers on this scale. All of our eight planets, the Sun, the aste...

Different models for the fracture toughness, K_IC, of porous materials have been proposed to describe K_IC as a function of the porosity P. They have in common that beside P at least one additional parameter exists that has to be adjusted to the measured data. Based on the cubic structure, we present a geometrical 3D model without any arbitrary par...

(Einleitung) Vor zwei Jahrzehnten wurde erstmals die These veröffentlicht, dass die drei Pyramiden in Gizeh die inneren drei Planeten unseres Sonnensystems Merkur, Venus und Erde repräsentieren [1, 2]. Dies beruht zum einen auf drei Gleichungen, die die Größen der drei Pyramiden präzise festlegen, zum anderen lässt sich die Anordnung der Pyramiden...

REMARK: The "full-text" only contains the cover page of the book! ------ (Klappentext) Seit langer Zeit schon geben uns die drei großen Pyramiden am Ursprung des Nildeltas Rätsel auf. Wie wurden sie errichtet? Warum in dieser Form, Anordnung und zu welchem Zweck? Was ist der Grund für die gewaltige Größe der Pyramiden? Gibt es einen astronomischen...

With regard to materials in nature having extraordinary properties, one focus of our research is nacre-inspired materials. On the basis of 3D-printing, it was possible to prepare tiny bending bars in order to be tested in three-point bending (3PB). However, their cross sections are not rectangular but have a special geometric shape. Therefore, anal...

Porous alumina layers were produced by colloidal processing of alumina with the addition of 15, 30, and 45 vol% polystyrene spheres (PS) as pore formers. Alumina laminates were designed with dense layers alternated with porous interlayers using 45 vol% of PS spheres and sintered at 1350°C. The layers’ thickness ranged from 2 to 15 μm with a random...

(Remark: Since the category postprint is not available, preprint has been chosen.) The analytical calculation of the area moments of inertia used for special mechanical tests in materials science and further generalizations for moments of different orders and broader symmetry properties has led to a new type of trigonometric power sums. The corresp...

The following astronomical tables serve as supplemental information for the publications Pyramiden, Planeten und Geheimkammern ‒ Die Planetenkorrelation von Gizeh [1], Planetary Correlation of the Pyramids at Giza and Teotihuacán ‒ P5 Program Description [2], and Pyramiden, Planeten und Geheimkammern II [3] (in preparation). The calculations were p...

Main objective of the presented research is the life time prediction of self-supporting flame-sprayed Al2O3- and Al2O3 -ZrO2 -TiO2-materials under constant load. The characteristic life time and its scatter were derived from stable crack growth tests and Weibull-statistics including the four-point-bending and ball-on-three-balls method. The potenti...

Tapes of TiO2‐MnO‐doped alumina (d‐Al2O3) and pure alumina (Al2O3) were shaped via tape casting. Laminates with three different layer numbers and respective thicknesses were produced and sintered at 1200°C. The microstructure and mechanical behavior of laminates were investigated and compared to the respective monolithic references (d‐Al2O3 and Al2...

Motivated by three-point bending tests with a nanoindenter and the necessary analysis, the area moment of inertia of tiny bending specimens, with a special "flower-shaped" cross section, is calculated analytically. If such cross sections have a four-fold rotational symmetry, it can be shown that a rotation of the cross section by any angle, with re...

3D printing is used to self‐assemble surface‐functionalized nanoparticles into supercrystalline macrostructures. The obtained columns feature high strength, favorably comparing to hierarchical composite materials, known for their exceptional mechanical properties. Further details can be found in the article, number 2000352, by A. John Hart, Gerold...

The room temperature handling of ceramic foam filters for steel melt filtration strongly depends on the mechanical properties of the materials. Against this background, the filter materials Al2O3, Al2O3 – C, and Al2O3–ZrO2 – TiO2 were compared regarding the crack growth exponent n, R-curve behaviour, and energy release during crack growth. Besides,...

The 3D-model published in the recent paper “A geometric model for the fracture toughness of porous materials” by Jelitto/Schneider (2018) is extended for the case of closed porosity with low density, like in polymer foams. At constant porosity, this model predicts the fracture toughness to be independent of the pore size. On the other hand, the wel...

In order to translate the exceptional properties of colloidal nanoparticles to macroscale geometries, assembly techniques must bridge a 10⁶‐fold range of length. Moreover, for successfully attaining a final mechanically robust nanocomposite macroscale material, some of the intrinsic nanoparticles’ properties have to be maintained while minimizing t...

R-curve and controlled stable crack growth behaviour of ZrB2–17vol.-%SiC and ZrB2–45vol.-%SiC ceramic composites was studied on V-notched samples using four-point bending at room temperature. The rising K1R behaviour was determined as a function of the crack extension Δa with a crack bridging mechanism being dominant in such behaviour. Significant...

We provide numerical experimental data and detailed information about the sample preparation and the experimental methods, used by different research groups for measuring the fracture toughness of porous materials. These data are supplemental information to the publication “A Geometric Model for the Fracture Toughness of Porous Materials,” [1], whi...

Due to their unique properties and structure, thermally sprayed ceramics are applied in many fields. Their applications range from engineering ceramics to the use in high temperature units, especially since an improved thermal shock performance was observed. The present study presents an analysis of structural and mechanical properties of thermal s...

A composite-laminate formed by thick layers (~ 320 µm) of zirconia-toughened alumina (ZTA) with thin (~ 50 µm) interlayers of zirconia partially stabilized (Y-PSZ) has been fabricated by tape casting and pressureless sintering. Fracture behavior and strength has been investigated and compared to a “monolithic” reference, e.g. a stack of zirconia-to...

Multi-walled carbon nanotubes (MWNT) and tungsten disulphide nanotubes (WS2-INT) have been widely used to improve the strength and toughness of composite materials. The mechanisms of such improvements are extensively studied, but it is not often clear what prompts a specific reinforcement mechanism to work. In this work we prepared two similar syst...

Room temperature time dependent static and cyclic fatigue of ZrB2-32 vol% SiC and ZrB2-45 vol% SiC particulate ceramic composites has been studied. It was established that the presence of the grain bridging mechanism acting during static and cyclic loading plays an important role in determining a lifetime and overall time dependent mechanical perfo...

The influence of preexisting defects and the generation of new ones during flash sintering was studied in 3YSZ. Weibull statistics was used to analyse mechanical testing data from flash and conventionally sintered specimens with equal densification. The obtained values for Weibull modulus and characteristic strength are 6.09 and 371 MPa for the con...

Recent studies have shown that layered silicate clays can be used to form a nacre-like bioinspired layered structure with various polymer fillers, leading to composite films with good material strength, gas barrier properties, and high loading capacity. We go one step farther by in situ growing metal nanoparticles in nacre-like layered films based...

Lead-free ferroelectric ceramics with 2 different compositions were produced using the mixed-oxide synthesis route. The electro-mechanical properties of samples doped with potassium sodium niobate (KNN) compositions of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 and (K0.43Na0.53Li0.04)(Nb0.84Ta0.10Sb0.06)O3 were characterised using the single edge V-...

Primarily, this presentation is a compilation related to the Mercury transit on May 9, 2016. Such a transit means that the planet Mercury passes in front of the solar disk as seen from the Earth. This happens about 13 to 14 times per century. However, these transits cannot always be observed, because daytime is needed and the sky should not be cove...

(Geringfügig revidierte fünfte Edition) Dieser Aufsatz befasst sich mit den Methoden der alternativen Altertumsforschung und speziell der alternativen Pyramidenforschung, deren Problematiken und deren Vorteil. In der klassischen Ägyptologie existieren bzgl. der Gizeh-Pyramiden noch viele ungeklärte Fragen. Beispielsweise gibt es bis heute eine auff...

Intergranular Nanostructure Effects on Strength and Toughness of Si3N4. -- Biljana Mikijelj, Zubair Nawaz, Jamie J. Kruzic, Juan Idrobo, Jeffrey J. Swab, Husseyin Özcoban, Hans Jelitto, Gerold A. Schneider, Theo Fett, and Yi Liu -- J. Am. Ceram. Soc., 98 [5], 1650–1657 DOI: 10.1111/jace.13484 (2015). -- In the recently published article the aut...

This report briefly describes and provides the Fortran source code of a parallelized version of the P4 program, based on “OpenMP,” which includes parallelization of the implemented VSOP87 subroutine. The P4 program is applied and described in detail in “Planetary Correlation of the Giza Pyramids – P4 Program Description.” The new version enables th...

Die folgenden astronomischen Tabellen dienen als Zusatzinformation zum Aufsatz „Pyramiden, Planeten und Geheimkammern ‒ Die Planetenkorrelation von Gizeh“ [1]. Eine zukünftige Ergänzung der Daten ist möglich. Die Berechnungen erfolgten mit dem Programm P4 auf der Basis der VSOP87-Theorie. Letztere ist für Merkur, Venus, das Erde-Mond-System und Mar...

We report on mechanical tests on interpenetrating-phase nanocomposite materials made by vacuum impregnation of nanoscale metal networks with a polymer. The metal component is nanoporous gold made by dealloying, whereas two epoxy resins and polyurethane are explored as the polymer component. The composites are strong and deformable in compression. A...

For more than 4500 years people have been fascinated by the pyramids of Giza. Now, there are very strong hints for a correlation between the three great pyramids in Giza and the three inner planets of our solar system: Mercury, Venus, and Earth. This assumption originally was based on three equations, connecting the sizes of the pyramids and planet...

Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE2O3 additions (RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La–Lu additions, but surprisingly were progressively lower for Y- and Lu-doped samples. The lower strength and toughness were associated wit...

This article contains additional information to the Report KfK-4960 (Kernforschungszentrum Karlsruhe, today: KIT), published by V. Corcalciuc and the author in 1991. Therein, the Quasi Free Break-up Model, introduced originally by Robert Serber, was used to calculate triple differential cross sections for particle-particle coincidences in nuclear b...

In order to develop and verify a dielectric breakdown model for bulk insulators thicker than 100 μm, the knowledge of the dominating conduction mechanism at high electric fields, or respectively voltages, is necessary. The dielectric breakdown is the electrical failure of an insulator. In some existing breakdown models, ohmic conduction is assumed...

The breakdown strength as well as the mechanical strength of ceramic materials decreases with increasing volume. The volume-effect of the mechanical strength can be explained by the Weibull theory. For the breakdown strength the same explanation has been often assumed. In order to validate this assumption breakdown strength and mechanical strength...

In this work, the compressive elastic modulus and failure strength values of bovine enamel at the first hierarchical level formed by hydroxyapatite (HA) nanofibers and organic matter are identified in longitudinal, transverse and oblique direction with uniaxal micro-compression method. The elastic modulus values (∼70 GPa) measured here are within t...

Ceramic composites found in nature, such as bone, nacre, and sponge spicule, often provide an effective resolution to a well-known conflict between materials' strength and toughness. This arises, on the one hand, from their high ceramic content that ensures high strength of the material. On the other hand, various pathways are provided for stress d...

The main idea is that a correlation exists between the three inner planets and the three pyramids of Giza. Now, this correlation has been extended to the inner system of chambers and corridors in the Cheops Pyramid. Interestingly, this correlation precisely defines a "Sun position" and a "Mars position" within the pyramid. Are these locations candi...

In the present study, the fracture toughness and the corrosion behaviour of particle reinforced alumina-steel composites were investigated. Composites, only differing in their type of matrix steel, were produced by Ti-activated pressureless infiltration. The aim was to clarify the influence of the matrix phase on the electrochemical properties as w...

Zur Anordnung und Größe der Pyramiden von Gizeh wurde eine Planetenkorrelation entdeckt. Die drei Pyramiden, benannt nach den Pharaonen Mykerinos, Chefren und Cheops, scheinen in dieser Reihenfolge den inneren drei Planeten des Sonnensystems zu entsprechen: Merkur, Venus und Erde. Die Pyramidenanordnung definiert anscheinend eine Konstellation der...

Fracture mechanical investigations of non-conducting, air-filled cracks in piezoelectric ceramics require knowledge of the electrical permeability of the crack gap. It is well known from experiments that this electrical permeability is significantly greater than the electrical permeability of an air-filled gap with smooth faces as considered in com...

The Single Edge V-Notched Beam (SEVNB) method is a well-known method to determine the R-curve of a material. Knowing the applied force and the corresponding crack length, the fracture toughness can be calculated easily under the assumption of a straight crack front. However, the crack front usually exhibits a curved shape when growing in a stable m...

The bulk breakdown behaviour of alumina single crystals with two different crystal orientations, {1 1 2¯ 0}-plane (single crystal A) and {0 0 0 1} -plane (single crystal C), have been studied. Therefore, plan-parallel single crystal samples were electrically loaded until dielectric breakdown was achieved. For each crystal orientation, a characteris...

Stable crack advance is required for a reliable crack growth resistance (R-Curve) measurement. In bending experiments, manual control of the mechanical load and observation of the growing crack is still being done by the operator. This work presents an approach to partly and fully automated R-curve measurements, where stable crack growth is achieve...

The present work investigates the influence of small AC, unipolar cyclic and DC electric loads on the fracture toughness of a ferroelectric ceramic. Single-edge-notched beams (SENB) of a poled and unpoled lead zirconate titanate (PZT) ceramic were fractured in a four-point-bending device under conditions of controlled crack growth. During crack adv...

The present work investigates the static and time dependent electric potential distribution around cracks in a poled ferroelectric ceramic by Kelvin Probe Force Microscopy (KFM). In a first step a Vickers indentation crack in poled lead zirconate titanate (PZT) was subjected to static electric fields of up to 500V/mm in poling direction, and the po...

High-toughness, high-strength ceramics, such as self-reinforced Si3N4, derive their superior mechanical properties from microstructures that promote very steeply rising R curves. Furthermore, accurately evaluating the R curve at the earliest stages of crack growth is necessary for correctly understanding, and predicting, the mechanical behavior. Co...

When measuring the fracture toughness of ceramics, for instance with the Single Edge V-Notched Beam (SEVNB) method, a known problem is given by the finite notch root radius. If this radius is larger than a certain small value of a few micrometers, the measured stress intensity factor is higher than the true intrinsic value. Another problem is that...

Das Verfahren und die Vorrichtung dienen zur Bestimmung von Risswiderstandskurven von Werkstoff-Proben. Die Probe wird in eine Messeinrichtung eingesetzt und mit einer Biegekraft beaufschlagt. Sowohl die Biegekraft als auch mindestens ein rissabhängiger Parameter werden gemessen. Anschließend werden die Messwerte in die Risswiderstandskurve transfo...

The fracture behaviour of metal-piezoceramic interfaces under mechanical and electrical loading is examined by four point bending using commercial multilayer actuators. The experiments are performed under stable crack growth in a custom made very stiff testing machine. Besides mechanical loading, a constant electric field was methodically switched...

The procedure for R-curve measurements on silicon nitrides obtained by a high-resolution compliance method to evaluate the bridging stress was reported. Material (Y 2O 3, MgO)-SN, a silicon nitride, was used for this study and consolidated in a two-step sintering process. Green bodies were uniaxially pressed and subsequently cold- isostatically den...

The objective of this work is to present the first results with a new technique for controlled fracture experiments, which allows for a more detailed detection of energetic mechanical processes in the specimen. In order to obtain conditions of stable crack growth in brittle materials a very stiff four-point-bending-device was constructed. In additi...

Crack-opening displacements (COD) method was used to measure crack-tip toughness in silicon nitride Si 3N 4 ceramics containing (Y 2O 3,Mg O) and (Y 2O 3, Al 2O 3). The R-curves for these materials were measured in a very stiff test device and four-point bending tests were carried out on notched bars of dimensions. Results for the first microns of...

In experimental R-curve investigations crack development usually starts from notches. The validity of R-curves depends on the size of the notch root radius. This influence is ignored in many cases. In this study it will be shown how the notch radius affects the formally computed crack resistance curve and how the initial true R-curve can be obtaine...

The fracture behavior of conducting cracks in PZT (PIC 151) was investigated under combined mechanical and electrical loads in four-point bending. Controlled crack growth in a single-edge V-notch beam (SEVNB) specimen was achieved in a very stiff displacement controlled device. During the experiments a constant electric field was applied. The mecha...

Four-point-bending V-notched specimens of lead zirconate titanate (PZT) poled parallel to the long axis are fractured under conditions of controlled crack growth in a custommade device. In addition to the mechanical loading electric fields, up to 500 V/mm are applied parallel and anti-parallel to the poling direction, i.e., perpendicular to the cra...

The fracture behavior of piezoelectric ceramic (PZT) as well as metal/PZT interfaces under mechanical and electric loading is examined in four and three point bending under conditions of controlled crack growth (see Fig. 1). The experiments are performed in a custom made very stiff testing machine. A special modulation technique, i.e. a small signa...

The fracture behavior of piezoelectric ceramic (PZT) as well as metal/PZT interfaces under mechanical and electric loading is examined in four-point-bending under conditions of controlled crack growth. The experiments are performed in a custom made very stiff testing machine. The experimental data, revealed at the interfaces, are compared with FEM-...

(Einleitung): Die drei großen Pyramiden von Gizeh stellen das letzte noch stehende der antiken sieben Weltwunder dar. Wie in der Antike, so existieren heute für den staunenden Laien als auch für die moderne Forschung eine Reihe ungelöster Fragen. Dieser Beitrag handelt von neuen ungewöhnlichen Entdeckungen, welche, sollten sie sich bewahrheiten, di...

The total (linear) energy release rate for crack growth in PZT ceramics and metal/ceramics interfaces is experimentally determined using a special modulation technique. In order to achieve stable crack growth a very stiff testing machine has been developed.

Two different designs of high fracture toughness micro-laminate ceramics were produced containing 50 μm thick Si3N4 layers and 100 μm thick Si3N4 + TiN layers. The first design with external tensile layers had a predicted maximum apparent fracture toughness of 10.5 MPa m^1/2. The second design with external compressive layers had a predicted maximu...

[Remark: This article was published by the Argo-Verlag, Marktoberdorf, Germany, in Magazin 2000plus, Alte Kulturen Spezial - Pyramiden 27/221 (2006) 6-16] ------------ Kurzfassung: Der vorliegende Aufsatz befasst sich mit der geometrischen Form der Cheops-Pyramide in Gizeh. In der Ägyptologie wird der gemessene Böschungswinkel der Pyramide (51°50'4...

An experimental method is presented, which allows for measuring all components of the total energy release rate under conditions of controlled crack growth in a piezoelectric material. V-notched specimens of PZT poled parallel to the long axis are fractured in 4-point-bending. Additionally electric fields are applied parallel and anti-parallel to t...

Risse an oder in dünnen Metallelektroden stellen eine Ausfallursache für Piezo-Aktoren dar. Von Interesse sind daher die das stabile Risswachstum bestimmenden bruchmechanischen Parameter für den Piezokeramik-Elektroden-Grenzflächenriss. Die bruchmechanischen Parameter werden theoretisch und experimentell bestimmt. Die Messung der zu einem Rissforts...

In 4-Punkt-Biegung wird in längs gepolten und angekerbten PZT-Biegestäbchen ein makroskopischer Riss mit Hilfe einer eigens entwickelten Apparatur kontrolliert getrieben. Zusätzlich zur mechanischen Last wird ein elektrisches Feld parallel bzw. antiparallel zur Polungsrichtung angelegt. Dies stellt eine für die Anwendung von piezo- bzw. ferroelektr...

Four point bending samples were poled parallel to the long axis, notched and fractured. During mechanical loading, a constant electric field was applied parallel or antiparallel to the poling direction (perpendicular to the crack surface). Assuming electrical crack boundary conditions of (i) an impermeable or (ii) a completely permeable crack, the...

Approximate intensity factors are calculated in four point bending by combination of the nonlinear piezoelectric Griffith crack solution with linear finite element solutions for the impermeable and completely permeable edge crack problem.

Motivation: --> Fracture strength and fracture toughness are important properties characterizing the mechanical resistivity of the material. --> Fracture toughness of many ceramic materials depends on the crack length, especially at small length scales of < 50 µm (R-Curve). --> R-Curves contain valuable information about strength behaviour and toug...

[Remark: This article was published by the Argo-Verlag, Marktoberdorf, Germany, in Magazin 2000plus Spezial 6/156 (2000) 12-22] ------------ Kurzfassung: Antike Bauwerke wurden wiederholt auf astronomische Zusammenhänge hin untersucht, so z. B. ihre Ausrichtung in Bezug auf die Bewegung von Sonne oder Sternen. Vor diesem Hintergrund wurden für die...

In der klassischen Ägpytologie werden die zweite und dritte große Pyramide in Giza den Pharaonen Chefren und Mykerinos zugeschrieben. Dieser Aufsatz behandelt die geometrischen Eigenschaften der Formen beider Pyramiden und deren Größen. Während die Form der Chefren-Pyramide bekanntermaßen auf das pythagoräische Tripel (3, 4, 5) zurückgeführt wird,...

Die Cheops-Pyramide ist eines der Bauwerke der Antike, das am genauesten vermessen wurde. Über die Deutung ihrer geometrischen Form wird seid über 100 Jahren spekuliert. Im vorletzten Jahrhundert hat der schottische Astronom Piazzi Smyth in einem seiner Bücher die These diskutiert, die Große Pyramide besitze anstelle der regulären Form eine gewisse...