The Annals of “Dunarea de Jos” University of Galati. Fascicle IX, Metallurgy and Materials Science

Temperature Effects on the Dimensions of CoCr Alloys: Dilatometric Study

Mirabela Georgiana MINCIUNĂ — 2026-03-15

Cobalt-chromium (Co-Cr) alloys are widely employed in biomedical and dental applications due to their favourable mechanical properties, corrosion resistance, and thermal stability. This study investigates the effect of silicon (Si) addition on the chemical composition and dimensional behavior of Co-Cr alloys, with an emphasis on their suitability for removable partial denture frameworks. A series of Co-Cr alloys with variable Si content (0.5–7.05 wt.%) were analysed using optical emission spectrometry and dilatometry to establish correlations between composition and thermal expansion.
The experimental approach provides new insights into how silicon content modifies the thermal behavior and dimensional stability of Co-Cr alloys during heating up to 1200 °C. The novelty of this research lies in the systematic evaluation of Si addition as a compositional variable in Co-Cr dental alloys, which has not been extensively explored in relation to dilatometric behavior. The study demonstrates that controlled silicon enrichment not only reduces the linear thermal expansion coefficient but also enhances structural stability during thermal cycling, minimizing the risk of deformation or mismatch with low-fusing dental ceramics. These findings bridge the gap between alloy chemistry and thermal compatibility, offering a scientific basis for optimizing alloy formulations used in precision dental restorations.

The outcomes provide valuable guidelines for the development of advanced Co-Cr-Si alloys with improved dimensional accuracy and thermal performance, contributing to the reliability and longevity of metal-ceramic prosthetic components.

Failure Case Study Series Part One: Analysis of Oxygen Compressor Shaft Breakage

Liviu GURĂU — 2026-03-15

This paper presents the results of a failure analysis of an oxygen compressor shaft using seven basic steps. The findings of this work form the basis for corrective and preventive actions to enhance equipment reliability and prevent future recurrence. The paper also offers a simple and direct approach to determine the root cause of structural component failure.
Visual inspection, specimen selection and preservation, high-stress area identification, chemical analysis with comparison to standards, hardness testing, optical microscopy, scanning electron microscopy (SEM), and EDS analysis were performed. A comprehensive metallurgical analysis of the oxygen compressor shaft failure provided substantial insights into the underlying mechanism, indicating shaft misalignment and bending-induced fatigue as the primary causes, with poor steel quality contributing to faster crack initiation and propagation.

Analysis and Prognosis of Surface Subsidence in the Jiu Valley

Dacian Paul MARIAN — 2026-03-15

Surface subsidence resulting from underground mining activities is a critical environmental and engineering concern that has garnered substantial attention in both academic and practical contexts. The phenomenon occurs when the removal of underground materials, such as coal, minerals, or ores, leads to the collapse or settling of the surface. This study examines mining operations conducted within the thick coal seams of the Jiu Valley Coal Basin in Romania, which utilize longwall mining techniques featuring roof control through caving or top coal caving methods. The analysis focuses on the complex deformations of the ground surface that have occurred over time as a direct result of coal extraction activities in specific mining sectors of the basin. Furthermore, the phenomenon of ground surface subsidence is investigated using the CESAR-LCPC finite element code. The modeling is conducted under the assumptions of elastic and elasto-plastic behavior. A temporal analysis of ground surface deformation is also conducted using a profile function. The results obtained from the modeling are subsequently compared with a comprehensive dataset of in situ measurements.

Additively Manufactured TPU Acoustic Metamaterials for High-Frequency Noise Mitigation in Dental Rotary Instruments

Emilian CHIFOR — 2026-03-15

Noise generated by high-speed dental turbines represents a persistent challenge in dental clinics, affecting both patient comfort and the occupational well-being of medical staff. This study investigates the potential of additively manufactured thermoplastic polyurethane (TPU) acoustic metamaterials for highfrequency noise mitigation in dental applications. A layered metamaterial panel based on periodic hexagonal unit cells is proposed and numerically evaluated as a compact and frequency-selective acoustic treatment. A vibro-acoustic simulation framework is employed to assess the sound transmission loss (STL) performance of the proposed metamaterial in comparison with a solid TPU panel of equivalent thickness. Two configurations are analysed: a reference case without acoustic treatment and a modified case in which the TPU-based metamaterial is integrated onto the head of a dental rotary bur. Overall, the findings highlight the effectiveness of compact TPU-based acoustic metamaterials as a promising solution for targeted noise mitigation in dental environments. The proposed approach combines acoustic efficiency, design flexibility, and compatibility with additive manufacturing, thereby facilitating its potential integration into dental equipment and clinical noise control strategies.

Buildings of the Future: Challenges or Opportunities?

Simona STANCA — 2026-03-15

The accelerated evolution of technology, the pressures generated by climate change, and global socio-economic transformations have led to a profound reassessment of the way residential buildings are designed and used. This paper analyses the concept of "buildings of the future" from the perspective of residential housing, highlighting both the challenges and opportunities associated with their implementation. Issues related to digitalization, sustainability, innovative materials, social impact, and urban integration are addressed, with the aim of assessing whether these transformations represent real progress or an obstacle to contemporary society.

Structure–Morphology–Defect Relationships in CaTiO₃-Based Perovskites for Environmental Applications

Adriana-Gabriela SCHIOPU — 2026-03-15

This review provides a comprehensive and critical analysis of the structure–morphology–defect relationships in CaTiO₃-based perovskites, with an emphasis on their environmental applications, particularly in water treatment and photocatalytic degradation processes. The paper systematically examines the influence of crystal structure, synthesis routes, microstructural evolution, and defect chemistry on the functional performance of CaTiO₃ materials. Special attention is given to the role of crystallographic phase stability, particle size distribution, surface area, porosity, and aggregation phenomena in controlling adsorption capacity and charge carrier dynamics. Different synthesis strategies—including solid-state reaction, sol–gel processing, hydrothermal and microwave-assisted routes, spray pyrolysis, and green mechanochemical methods—are comparatively evaluated with respect to their effects on morphology control and defect formation. Furthermore, the integration of CaTiO₃ with carbon-based materials and the development of doped or composite systems are analysed as strategies for enhancing photocatalytic activity and environmental stability.
By correlating structural features with the physicochemical performance indicators reported in the literature, this review identifies current limitations, unresolved challenges, and promising directions for future research. The analysis aims to provide a coherent framework for the rational design and optimization of CaTiO₃-based perovskites in environmental remediation technologies.

Experimental Evaluation of Patterned Reflective Surfaces for Solar Glare Reduction in Small UAV Platforms

Florin-Bogdan MARIN — 2026-03-15

Small unmanned aerial vehicles (UAVs) increasingly require optical signature control in order to reduce visual detectability during daylight operations. This study investigates the influence of mirror-type polymer surface treatments on solar glare behavior and proposes a patterned reflective configuration as a passive mitigation strategy. A small multirotor UAV platform was partially covered (35–40%) with a PET-based reflective film exhibiting high specular reflectance (approximately 80–85%), and its visual response was evaluated under direct solar illumination.
Experimental observations indicated that continuous mirror-like surfaces generate intense specular glints for surface–sun incidence angles between approximately 20° and 45°, with glare visibility durations of 1.5–2.0 seconds. To reduce glare intensity, a segmented surface pattern was introduced, decreasing the estimated effective specular area from 30–35% to 15–20%. The patterned configuration demonstrated a shorter glare duration (0.5–0.8 seconds) and a proportional reduction in glare alignment probability. The results indicate that while reflective polymer coatings may contribute to background blending under diffuse lighting conditions, continuous mirror-like surfaces increase detection risk under direct sunlight. Patterned segmentation represents a low-cost, geometrybased approach for solar glint mitigation and optical camouflage enhancement in small UAV platforms.