Compressive properties of cell structures manufactured by photo-curing technology liquid polymer resins – Polyjet Matrix

The article presents the results of compressive strength tests of cylindrical samples with a hexagonal cell structure. The samples were made of MED 610 material using the photo-curing technology liquid polymer resins. The compressive strength was estimated on the basis of a static compression test of the printed elements. It has been shown that the PolyJet Matrix 3D printing technology enables the printing models with a thin-walled cell structure, which, while maintaining the appropriate strength properties, can be used in the design and production of certain utility models.

Evaluation of the Effects of Different Composite Types on the Shear Bond Strength: An in vitro Study

Introduction: The aim of this in vitro study was to determine and compare the shear bond strength (SBS) of two types of composites. Material and Methods: Twenty cylindrical samples were prepared and divided into two control and case groups. The case group consisted of 10 cylindrical samples of two types of composites (3M and Vivadent), and the control group, which was divided into two subgroups of 5, included only one type of composite (3M or Vivadent). After preparation, the samples were transferred to the Instron device for testing the SBS. The data were analyzed by SPSS version 15 software using Smirnov-Kolmogorov test for studying the normal distribution of data and t-student test for independent populations. Results: Heliomolar (Ivoclar-Vivadent) composite (microfill) showed the lowest SBS, but the difference was not significant (P>0.05). The highest SBS was for Filtek Z100 (3M ESPE) composite. There were no fracture lines in the interface of the two composites. Conclusion: This confirms that proper use of adhesives can prevent fracture in the interface of different composites. So, using two different composite brands on each other does not reduce the bond strength between them.

3D Numerical Modelling of the Application of Cemented Paste Backfill on Displacements around Strip Excavations

This article presents laboratory and spatial numerical modeling of cemented paste backfill. The first part of the research concerned laboratory tests of a mixture of sand, water, and variable cement content (5%, 10%, and 15%). The density and curing time of the mixture were determined. Moreover, cylindrical samples with a diameter of 46 mm and a height of 92 mm were constructed, for which compressive and tensile strength were calculated after one, two, three, and four weeks. The second part of the research concerned 3D numerical modeling with the use of RS3 software. For the exploitation field with dimensions of 65 m × 65 m, a strip-mining method was designed. The main objective of the research was to determine the changes in displacements around the haulage room and transportation roadway located in the immediate vicinity of the exploitation field. For the first time in numerical modeling, a two-sided strip method was used for the four stages of mining the ore deposit where the post-mining space was filled with a cemented paste backfill. Based on this research, the compressibility coefficient was determined.

Flexural Strength and Depth of Cure of Single Shade Dental Composites

Aims: This work aims to assess the flexural strength and depth of cure of Optishade, Omnichroma and Z350 dental resin composites. Study Design: Experimental Laboratory Study. Methods: To assess flexural strength as per ISO standards, 15 samples of each of the three materials were made (n=5) with the dimensions 25x2x2 mm. They were then subjected to 3 point bending testing on a universal testing machine. To assess depth of cure as per ISO standard, 15 cylindrical samples 4 mm in diameter and 6 mm in height were created (n=5) and scraping test was performed. Results: There was a significant difference between the 3 materials in both flexural strength and depth of cure. Z350 had the lowest depth of cure and the highest flexural strength. Conclusion: Within the limitations of this study, all three tested materials fell within the ISO requirementsfor dental resin compositesfor both flexural strength and depth of cure.

Kinematics of steam film wetting while quenching cylindrical samples in thermal oils

The paper presents the determination of the velocity of the vapor front along the outer wall of a cylindrical specimen in the process of two-dimensional axisymmetric quenching of the samples in thermal oils. One thermal oil is Isorapid 277 HM heated to 40°C and the other thermal oil is Marquench 722 heated to 90°C. The experimental setup of the work consists of heating to a temperature of 850°C, then quenching three dimensionally different cylindrical probes. The dimensions of the probe were: ϕ25x100 ϕ50x150 and ϕ75x225 mm. All quenchings were done in strictly controlled conditions of the flow rate of the quenchant around the cylinder as well as maintaining the temperature of the quenchant within the maximum 40±2.5°C or 90d3°C, during the quenching of the samples. The velocity of movement of the steam front on the outer surface of the cylinder was determined from the time-measured values of temperatures at the marked points of each sample. The analysis of the steam front movement velocity along the cylinder wall starts from the moment the lower base of the probe touches the quenchant. During the process of immersing the test probe in the quenchant, in addition to measuring the temperatures in time, the time of lowering the probe to contact with the quenchant sample was also measured. The approximate average velocity of the vapor front was determined based on the indications of the lower and middle thermocouples located 1.5 mm below the outer surface of the cylinder wall. Based on the distance of one half the height of each probe and time, the velocity of the steam film movement or the kinematics of the steam film wetting was obtained. The obtained results were compared with the results of quenching in water and aqueous solutions of the same probes under the same strictly controlled conditions.

Reduced Scale Experimental Modelling of Distributed Thermal Response Tests for the Estimation of the Ground Thermal Conductivity

The knowledge of the ground thermal properties, and in particular the ground thermal conductivity is fundamental for the correct sizing of the Ground Coupled Heat Pump (GCHP) plant. The Thermal Response Test (TRT) is the most used experimental technique for estimating the ground thermal conductivity. This paper presents an experimental setup aimed to realise a suitable scale prototype of the real borehole heat exchanger (BHE) and the surrounding ground for reduced scale TRT experiments. The scaled ground volume is realised with a slate block. Numerical analyses were carried out to correctly determine suitable geometric and operational parameters for the present setup. The scaled heat exchanger, inserted into the block, is created with additive technology (3D printer) and equipped with a central electrical heater along its entire depth and with temperature sensors at different radial distances and depths. Present measurements highlight the possibility to reliably perform a TRT experiment and to estimate the slate/ground thermal conductivity with an agreement of about +12% with respect to measurements provided by a standard commercial conductivity meter on proper cylindrical samples of the same material and onto 10 different portions of the slate block.

Effect of sample geometry and aggregate type on expansion due to alkali-silica reaction

Late expansions due to alkali-silica reaction were observed in field samples for some aggregates and supplementary cementing materials (SCM) combinations despite meeting the 2-year expansion criterion of the concrete prism test. This fosters a research into the effect of sample geometry and aggregate reactivity on alkali leaching and expansion of lab samples. Larger samples showed less leaching compared to standard prisms. Cylinders of 100 mm-diameter showed higher expansion than 75 mm-standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. Alkali leaching from concrete samples and alkali release from some aggregates could lead to cylindrical samples having higher expansion and better correlation to field samples compared to standard concrete prisms.

Echogenic Advantages of Ferrogels Filled with Magnetic Sub-Microparticles

Ultrasonic imaging of ferrogels (FGs) filled with magnetic nanoparticles does not reflect the inner structure of FGs due to the small size of particles. To determine whether larger particle size would improve the acoustic properties of FGs, biocompatible hydrogels filled with 100–400 nm iron oxide magnetic sub-microparticles with weight fraction up to 23.3% were synthesized and studied. Polymeric networks of synthesized FGs were comprised of chemically cross-linked polyacrylamide with interpenetrating physical network of natural polysaccharide—Guar or Xanthan. Cylindrical samples approximately 10 mm in height and 13 mm in diameter were immersed in a water bath and examined using medical ultrasound (8.5 MHz). The acoustic properties of FGs were characterized by the intensity of reflected echo signal. It was found that the echogenicity of sub-microparticles provides visualization not only of the outer geometry of the gel sample but of its inner structure as well. In particular, the echogenicity of FGs interior depended on the concentration of magnetic particles in the FGs network. The ultrasound monitoring of the shape, dimensions, and inner structure of FGs in the applied external magnetic field is demonstrated. It is especially valuable for the application of FGs in tissue engineering and regenerative medicine.

Effect of sample geometry and aggregate type on expansion due to alkali-silica reaction

Late expansions due to alkali-silica reaction were observed in field samples for some aggregates and supplementary cementing materials (SCM) combinations despite meeting the 2-year expansion criterion of the concrete prism test. This fosters a research into the effect of sample geometry and aggregate reactivity on alkali leaching and expansion of lab samples. Larger samples showed less leaching compared to standard prisms. Cylinders of 100 mm-diameter showed higher expansion than 75 mm-standard prisms; however, both sample shapes showed similar expansions for one tested aggregate when used with SCM. Alkali leaching from concrete samples and alkali release from some aggregates could lead to cylindrical samples having higher expansion and better correlation to field samples compared to standard concrete prisms.