Experimental and numerical characterization of imperfect additively manufactured lattices based on triply periodic minimal surfaces

Lattices based on triply periodic minimal surfaces (TPMS) are attracting increasing interest in seminal industries such as bone tissue engineering due to their excellent structure-property relationships. However, the potential can only be exploited if their structural integrity is ensured. This requires a fundamental understanding of the impact of imperfections that arise during additive manufacturing. Therefore, in the present study, the structure-property relationships of eight TPMS lattices, including their imperfections, are investigated experimentally and numerically. In particular, the focus is on biomimetic network TPMS lattices of the type Schoen I-WP and Gyroid, which are fabricated by laser powder bed fusion from the biocompatible alloy Ti-42Nb. The experimental studies include computed tomography measurements and compression tests. The results highlight the importance of process-related imperfections on the mechanical performance of TPMS lattices. In the numerical work, firstly the as-built morphology is artificially reconstructed before finite element analyses are performed. Here, the reconstruction procedure previously developed by the same authors is used and validated on a larger experimental matrix before more advanced calculations are conducted. Specifically, the reconstruction reduces the numerical overestimation of stiffness from up to 341% to a maximum of 26% and that of yield strength from 66% to 12%. Given a high simulation accuracy and flexibility, the presented procedure can become a key factor in the future design process of TPMS lattices

Structure-property relationships of imperfect additively manufactured lattices based on triply periodic minimal surfaces

Lattices based on triply periodic minimal surfaces (TPMS) have recently attracted increasing interest, but their additive manufacturing (AM) is fraught with imperfections that compromise their structural integrity. Initial research has addressed the influence of process-induced imperfections in lattices, but so far numerical work for TPMS lattices is insufficient. Therefore, in the present study, the structure–property relationships of TPMS lattices, including their imperfections, are investigated experimentally and numerically. The main focus is on a biomimetic Schoen I-WP network lattice made of laser powder bed fusion (LPBF) processed Ti-42Nb designed for bone tissue engineering (BTE). The lattice is scanned by computed tomography (CT) and its as-built morphology is examined before a modeling procedure for artificial reconstruction is developed. The structure–property relationships are analyzed by experimental and numerical compression tests. An anisotropic elastoplastic material model is parameterized for finite element analyses (FEA). The numerical results indicates that the reconstruction of the as-built morphology decisively improves the prediction accuracy compared to the ideal design. This work highlights the central importance of process-related imperfections for the structure–property relationships of TPMS lattices and proposes a modeling procedure to capture their implications

Reformation als Kommunikationsprozess

Beim Hussitismus bzw. Utraquismus in Böhmen und der reformatorische Bewegung ab 1517 in Sachsen handelt es sich um zwei unterschiedliche Reformationen, jedoch mit einer Fülle von sachlichen und personalen Verbindungslinien. Diese rücken im vorliegenden Band erstmalig in einen gemeinsamen Fokus.»Wir sind alle Hussiten«, bekannte Martin Luther 1520 nach der Lektüre von Schriften des tschechischen Reformators Jan Hus, der gut einhundert Jahre zuvor als Ketzer verbrannt worden war. Die beiden Reformatoren verbinden, ebenso wie die von ihnen ausgehenden Erweckungs- und Erneuerungsbewegungen, viele Ähnlichkeiten, Übereinstimmungen und parallele Entwicklungsverläufe. Dennoch werden sie meist getrennt betrachtet. Der Sammelband analysiert Aspekte der Reformation in Böhmen und Sachsen und rückt so die beiden religiösen Brennpunkte in einen gemeinsamen Fokus. Methodisch wählen die Beiträgerinnen und Beiträger dabei einen kommunikationsgeschichtlichen Zugang

Precipitation in the Mediterranean Region Observed with TRMM Microwave Data

Self-organized networks require some mechanism to ensure cooperation and fairness in the face of individual utility maximizing users and potential malicious attacks. Otherwise, network performance can be seriously deteriorated. One promising approach are decentralized reputation systems. However, these are vulnerable to users with an interest in passing on false information. Robustness against liars has not yet been analyzed in detail. In this paper, we provide a first step to the robustness analysis of a reputation system based on the deviation test as introduced in [6]. Users accept second hand information only if this does not differ too much from their reputation values. We show that the system exhibits a phase transition: In the subcritical regime, the reputation system is robust and the lying has no effect. In the supercritical regime, the lying does have an impact. We obtain the exact critical values via a mean field approach. We then use explicit computation to verify the mean field results. Thus, we can give conditions under which the deviation test makes the reputation system robust. We also obtain quantitative results on what goes wrong in the supercritical regime

Analysis of the Algerian severe weather event in November 2001 and its impact on ozone and nitrogen dioxide distributions

An analysis of the severe weather event in November 2001 over the western Mediterranean is presented focusing on satellite-based trace gas measurements from the Global Ozone Monitoring Experiment (GOME) on board the European Remote Sensing Satellite (ERS-2). This study is supplemented by a synoptic analysis and simulations of the three-dimensional stratospheric chemical transport model ROSE. Arctic air masses moved rapidly from Scandinavia to the Iberian peninsula and were mixed with subtropical air over the still warm Mediterranean Sea. This caused severe thunderstorms and extreme rainfall along the coasts of Morocco and Algeria and later on the Balearic Islands. Associated with the meridional transport an intrusion of stratospheric air below 3 km above sea level was observed. The maximum potential vorticity (PV) derived from UK Meteorological Office analysis data was about 9.3 potential vorticity units (pvu) at 330 K at the equatorward position of 35°N. These very high values went along with remarkably enhanced total ozone levels obtained from GOME backscatter measurements of collocated GOME/ERS-2 overpasses. Further investigation of GOME data showed unusually high levels of nitrogen dioxide (NO2) above the western Mediterranean. We present a new method to derive the tropospheric content of nitrogen dioxide (NO2) from a combination of satellite measurements and results of a chemical transport model. We show that about two-third of the total atmospheric content of nitrogen dioxide in the observed plume is found in the troposphere, due to lightning activity, advection and vertical transport in the thunderstorms from the planetary boundary layer (PBL) to atmospheric levels above clouds

Effect of Atmospheric Variability and Aircraft Flight Parameters on the Refraction of Sonic Booms

This study deals with the potential audibility of sonic booms from supersonic aircraft at the ground as a consequence of the aircraft flight parameters and the atmospheric variability. A ray tracing model is used to decide whether a sonic boom emitted downwards by a high flying supersonic aircraft hits the ground or is refracted upwards before it reaches the ground. Aircraft altitude, speed, and flight direction are systematically changed within realistic ranges. The meteorological data rely on a homogeneous reanalysis dataset for eleven years over the domain of Europe with a very high vertical resolution. The cases of sonic booms hitting or not hitting the ground are identified for various situations and respective frequency distributions are derived. In addition, the angle of incidence of rays arriving at the ground and the turning-level height of rays not reaching the ground are studied as the intensity of sonic booms also depends on these parameters. It turned out that sonic-boom rays are refracted such that they do not reach the ground if the flight altitude is rather high (long propagation path) and the aircraft speed remains between Mach numbers of 1.05 and 1.25. Sonic-boom rays not reaching the ground are furthermore possible if the aircraft heading is mainly upwind, the temperature mostly increases along the propagation direction of the ray, and a wind speed maximum exists below flight level. The probability of sonic-boom rays not reaching the ground generally increases from north to south, but also depends on the season