Material characteristics of push-out tests Vanova, P; Orolin, P; Dubecky, D
IOP conference series. Materials Science and Engineering,
12/2021, Letnik:
1209, Številka:
1
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Abstract
Two types of push-out tests were carried out at the Centre of Research and Innovation in Construction, the Technical University of Košice - one at a composite based on steel continuous shear ...connector and the second one at the same connector, however made of glass-laminate material. For further research, the material characteristics of the material used needed to be found. In this article, the material tests performed as well as their results are presented.
Perfect graphene is believed to be the strongest material. However, the useful strength of large-area graphene with engineering relevance is usually determined by its fracture toughness, rather than ...the intrinsic strength that governs a uniform breaking of atomic bonds in perfect graphene. To date, the fracture toughness of graphene has not been measured. Here we report an in situ tensile testing of suspended graphene using a nanomechanical device in a scanning electron microscope. During tensile loading, the pre-cracked graphene sample fractures in a brittle manner with sharp edges, at a breaking stress substantially lower than the intrinsic strength of graphene. Our combined experiment and modelling verify the applicability of the classic Griffith theory of brittle fracture to graphene. The fracture toughness of graphene is measured as the critical stress intensity factor of and the equivalent critical strain energy release rate of 15.9 J m(-2). Our work quantifies the essential fracture properties of graphene and provides mechanistic insights into the mechanical failure of graphene.
This article focuses on the specifics in characterizing the properties of additively manufactured, cement-based materials in their hardening and hardened states. Such characterization is required for ...the material development, structural design, and quality control of both printable material and 3D-printed elements. The related challenges are associated with the printed material's layered structure, which results in higher degrees of anisotropy and inhomogeneity in comparison to conventionally cast concrete. Thus, in the production of test specimens, the particularities of the real-scale 3D-printing process must be considered. Here a distinction is made between the production of samples for material testing prior to or parallel to actual application and those extracted from full-scale elements. Specifics of destructive testing are analyzed with emphasis on mechanical characteristics, while the discussion of non-destructive testing mainly addresses the geometry of the deposited layers and printed elements, measuring deformations, and finding such defects as voids and gaps. Finally, approaches required for developing/adapting guidelines and standards for testing of 3D-printed, cement-based materials are discussed.
To investigate the insertion/pull-out performance of splints produced by hand casting, thermoforming, milling, and 3D printing.
A total of 120 identical mandibular splints (n = 8 specimens per group) ...were manufactured with hand casting, thermoforming, milling, and 3D printing. The splints were stored in water at 37°C for 10 days and then placed onto cobalt-chromium arches and fixed on one side. Forces were applied to the other side (centric, perpendicular 50 N, 1 Hz) at two different positions (teeth 46 and 44/45) to pull out, and the test was then reset. The number of pull-out cycles until failure was recorded. The fracture behavior of the splints was investigated and characterized as fracture in the loading position, fracture at the fixation, or combined fracture. Splints were pulled off until fracture as a control (v = 1 mm/minute). Finite element analysis was used to verify the results. Statistical analyses were conducted with one-way ANOVA, post hoc Bonferroni, Pearson correlation, and Kaplan-Meier log-rank tests (α = .05).
The mean pull-off cycles varied from 7,839 (V-Print) to 1,600,000 (Optimill) at the tooth 46 position (FDI numbering system) and from 9,064 (Splint Comfort) to 797,750 (Optimill) at the 44/45 position. Log-rank test showed significantly (P < .001) different pull-out cycles between the systems (chi-square: 61,792 to 122,377). The thickness of the splints varied between 1.6 ± 0.2 mm (Splint Comfort) and 2.3 ± 0.1 mm (V-Print). Thickness and number of cycles were correlated (Pearson: 0.164; P = .074). The pull-off forces of the control varied significantly (P ≤ .040), ranging from 13.0 N (Keysplint) to 82.2 N (Optimill) at the tooth 46 position and from 25.2 N (Keysplint) to 139.0 N (Optimill) at the 44/45 position.
The milled and cast splints survived more pull-off cycles than the printed or thermoformed splints. The pullout performance showed differences among the tested splint systems and indicated the influence of the material properties and processing.
A Perspective is presented on the history and current understanding of molecular gels and the factors that must be considered to characterize them. The abilities of the most important structural, ...dynamic, and rheological tools available currently to provide the information necessary to follow the formation of a molecular gel from its initial sol phase and then to define it at different distance and time scales are discussed. Approaches to determining a priori when a molecule will gelate a selected liquid, as well as possible methodologies for overcoming current limitations in understanding molecular gels, are presented. Finally, some of the many potential and realized applications for these materials are enumerated.
The study aimed to evaluate the effect of thickness on the translucency parameter (TP) and whiteness index for dentistry (WID) of single-shade resin composites compared with a multi-shade resin ...composite after thermocycling. A total of 100 resin composite samples of five brands (Filtek Z250, Omnichroma, Vittra APS Unique, Zenchroma, and Charisma Diamond One) with thicknesses of 2 mm and 4 mm were prepared (n=10). CIE L*a*b* coordinates were obtained using a spectrophotometer. The resin composite samples were subjected to 10,000 thermocycles. Before and after thermocycling, TP values were calculated with the CIEDE2000 formula, and whiteness values were calculated using the WID. The influence of thickness, resin composite, and aging on these variables was analyzed using the generalized linear model (p<0.05). Omnichroma and Filtek Z250 exhibited, respectively, the highest and the lowest TP00 values compared with the other resin materials (p<0.001). The TP00 values of Zenchroma and Diamond One were similar (p>0.05). Vittra APS Unique had a lower TP than Zenchroma and Diamond One (p<0.001). Before thermocycling, the highest WID showed the combination of Vittra APS Unique with thicknesses of 2 mm (48.33±1.18). After thermocycling, the highest WID was shown in the combination of Vittra APS Unique with thicknesses of 2 mm (45.33±0.55) and 4 mm (46.23±0.94) (p<0.001). After thermocycling, the lowest WID was for the combination of Filtek Z250 with thicknesses 2 mm (21.16±0.93) and 4 mm (20.70±0.91) (p<0.001). The TP and WID values of the resin composites varied across different composites and thicknesses. Single-shade resin composites of different thicknesses demonstrated higher translucency and whiteness values than multi-shade resin composite, both before and after thermocycling.
The closure and repair of wounds after traumatic or surgical injury is of significant clinical and research importance. While sutures remain the common wound closure technique, they have many ...disadvantages. Consequently, polymeric hydrogel adhesives have emerged as essential materials for wound management and repair because of their tunable chemical and physical properties, which enable them to adhere or stick to tissues, possess sufficient mechanical strength to stay intact and be subsequently removed, provide complete wound occlusion, and act as a barrier to bacterial infection. Moreover, these materials absorb wound exudates and keep the wound moist for faster healing. This tutorial review summarizes the key chemical features that enabled the development and use of polymeric hydrogels as wound adhesives, sealants, and hemostats, their design requirements, synthetic routes, determination of properties, and the tests needed to evaluate their performances. This tutorial review is a reference and a starting point for scientists and clinicians working or interested in the field of wound management and, importantly, for the general audience who is interested in polymers for medical applications.
By combining metal nodes with organic linkers we can potentially synthesize millions of possible metal–organic frameworks (MOFs). The fact that we have so many materials opens many exciting avenues ...but also create new challenges. We simply have too many materials to be processed using conventional, brute force, methods. In this review, we show that having so many materials allows us to use big-data methods as a powerful technique to study these materials and to discover complex correlations. The first part of the review gives an introduction to the principles of big-data science. We show how to select appropriate training sets, survey approaches that are used to represent these materials in feature space, and review different learning architectures, as well as evaluation and interpretation strategies. In the second part, we review how the different approaches of machine learning have been applied to porous materials. In particular, we discuss applications in the field of gas storage and separation, the stability of these materials, their electronic properties, and their synthesis. Given the increasing interest of the scientific community in machine learning, we expect this list to rapidly expand in the coming years.
Materials research for fusion Knaster, J; Moeslang, A; Muroga, T
Nature physics,
05/2016, Letnik:
12, Številka:
5
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Fusion materials research started in the early 1970s following the observation of the degradation of irradiated materials used in the rst commercial fission reactors. The technological challenges of ...fusion energy are intimately linked with the availability of suitable materials capable of reliably withstanding the extremely severe operational conditions of fusion reactors. Although ssion and fusion materials exhibit common features, fusion materials research is broader. The harder mono-energetic spectrum associated with the deuteriumtritium fusion neutrons (14.1 MeV compared to <2 MeV on average for ssion neutrons) releases signicant amounts of hydrogen and helium as transmutation products that might lead to a (at present undetermined) degradation of structural materials after a few years of operation. Overcoming the historical lack of a fusion-relevant neutron source for materials testing is an essential pending step in fusion roadmaps. Structural materials development, together with research on functional materials capable of sustaining unprecedented power densities during plasma operation in a fusion reactor, have been the subject of decades of worldwide research eorts underpinning the present maturity of the fusion materials research programme.
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