Non-destructive Laboratory Testing Research Articles

Testing the strength of thin feather-edge monolithic multilayered zirconia crowns: A pilot study with a novel acoustic test

Intoduction: Limited research has explored the mechanical characteristics of recently introduced multilayered monolithic zirconia (MZC) crowns with feather-edge margins design. Moreover, most of the conventional techniques for evaluating the mechanical behavior of brittle dental ceramics rely on destructive tests, making it impossible to precisely evaluate real strength values due to premature crack initiation detection failure. Objectives: The main objective of the study was to assess the load capacity of translucent multilayered monolithic zirconia crowns with feather-edge margin thicknesses of 0.4 mm and 0.5 mm. Additionally, the research introduced a novel non-destructive acoustic emission testing (AET) technique in the laboratory to identify early cracks in dental ceramics. Methods: Forty multilayered zirconia crowns produced using computer-aided design and computer-aided manufacturing (CAD/CAM) technology were evenly divided into two groups, each with distinct feather-edge margin thicknesses: 0.5 mm (group 1) and 0.4 mm (group 2). These crowns were securely cemented onto customized polymethyl methacrylate (PMMA) dies using a universal restorative glass ionomer. Subsequently, the crowns underwent a compressive axial loading test, controlled by an innovative AET crack detection system rooted in the principles of non-destructive laboratory testing. Fractographic analysis was conducted to determine the location of crack or eventual fracture. Results: The proportion of MZCs with a crack was statistically higher than the proportion with a fracture in the whole sample (p<0.001). In addition, the results showed that the crowns in group 1 exhibited higher loading values than those in group 2. The mean loading capacity in group was 911.2 N ± 614.7 N. Two locations of crack and fracture were registered: occlusal and marginal. No statistical association was observed between the two groups for the location of cracks or fractures. Conclusions: The feather-edge crowns with a 0.5 mm margin thickness had a higher loading capacity than those with a 0.4 mm. However, the latter supports loads that exceed occlusal force in the oral cavity suggesting that 0.4 mm feathered edge MZCs may be a valid and less invasive alternative to thicker margins. The novel load-to-fracture AET setup proved effective in detecting early crack initiation, suggesting it as a promising method for assessing the mechanical properties of brittle materials prior to failure, potentially impacting the field of dentistry. However more advanced research is needed to enhance the accuracy of the proposed technique. Clinical implications: The examined MZC demonstrates the ability to withstand occlusal forces in a patient’s mouth, offering clinical practitioners the option of embracing minimally invasive dentistry through the use of 0.4 mm feather-edge MZC in their treatment options. Furthermore, the positive results from the innovative acoustic emission testing technique, facilitating early crack detection, indicate a promising future for studying the behavior of brittle materials in dental laboratory testing.

Consolidating Efficiency of Nanolime Product CaLoSiL on Porous Limestone

The effects of the double and the multiple application (2 to 6) of Calosil® (IBZ-Salzchemie GmbH, Halsbruecke, Germany) E25, IP 25 and E50 products were studied on Maastricht limestone, which is characterized by high porosity and large pores. Both destructive and non-destructive laboratory tests we performed in order to assess the consolidating efficiency of the nanolimes—the bending and compressive strengths, ultrasound velocity measurement, porosity determination and SEM examination. Except for the compressive strength, the other characteristics were investigated in the depth profile of stone specimens to find the distribution of the treatment product within the substrate. The performed tests showed good penetration of CaLoSiL nanolime products into the studied limestone. The bending strengths of limestone samples after double treatment using nanolime E 25, IP25 and E 50 were found to be increased by 50%, 44% and 89%, respectively, whereas the compressive strength increased by 50%, 23% and 73%. The porosity of the stone was reduced by the treatment, but only slightly, to an acceptable extent. The higher sum of performed nanolime applications resulted in a higher strengthening effect but at the same time at the uneven distribution of the product in the stone specimen, which was followed by an increase in the strength and decrease of open porosity in the surface part. SEM examination showed a modification of the stone microstructure by the added binder.

Strength coefficient estimation by indirect methods

Introduction. In exploration, construction, and mining operations it is necessary to assess the physical and mechanical properties of rocks. However, laboratory rock tests are expensive, time-consuming, and require a large number of quality rock samples. There is a problem of rapid evaluation of physical and mechanical properties by indirect, non-destructive methods. The problem is considered on the example of one of the basic properties, the strength coefficient according to Protodiakonov's scale. Research methodology included the analysis of the main indirect methods of determining the strength coefficient based on strength, elastic and acoustic properties of rocks on the grounds of statistical empirical relationships of V. V. Rzhevskii, G. Ia. Novik, L. I. Baron; K. L. Ter-Mikaelian, A. I. Beron, and M. M. Protodiakonov. The most promising methods based on non-destructive laboratory tests of modulus of elasticity and longitudinal wave velocity are selected. Results and conclusions. The strength coefficient was calculated by several methods on the example of siliceous sandstones, selected from the exploration well of the gas-bearing field. The results were compared with each other and with cadastral references and materials. The most optimal for calculations were the dependences of V. V. Rzhevskii, G. Ia. Novik, and L. I. Baron when evaluating the strength coefficient by the modulus of elasticity, and the dependences of A. I. Beron and L. I. Baron when calculating based on acoustic characteristics.

Tsallis entropy modeling of Pressure Stimulated Currents when cement-based materials are subjected to abrupt repetitive bending loadings

Pressure Stimulated Currents (PSCs) are emitted while brittle materials of high electrical resistivity are subjected to mechanical loading. The PSCs are related to the generation of cracks and the consequent evolution of cracks’ network in the bulk of the specimen. In the experimental protocol described here cement-mortar beams of rectangular cross-section were subjected to Three-Point Bending (3PB) repetitive loading/unloading loops. The qualitative and quantitative characteristics of the recorded PSCs match corresponding recordings previously published. More specifically, during the load increase a spike-like PSC emission was recorded followed by a relaxation of the PSC, after reaching its final value. The relaxation process of the PSC was then studied in terms of non-extensive statistical physics (NESP) based on Tsallis entropy equation. The behavior of the Tsallis parameter was studied in relaxation PSCs in order to investigate its potential use as an index for monitoring the crack evolution process with a potential use in non-destructive laboratory testing of cement-based specimens of unknown internal damage level. This analysis of the experimental data indicated that the value of the entropic index q exhibits a characteristic decrease attaining the critical value of 1.25 while reaching the ultimate strength of the specimen, and thus could be used as a forerunner of the expected failure.

Predicting fracture of mortar beams under three-point bending using non-extensive statistical modeling of electric emissions

Weak electric signals termed as “Pressure Stimulated Currents, PSC” are generated and detected while cement based materials are found under mechanical load, related to the creation of cracks and the consequent evolution of cracks’ network in the bulk of the specimen. During the experiment a set of cement mortar beams of rectangular cross-section were subjected to Three-Point Bending (3PB). For each one of the specimens an abrupt mechanical load step was applied, increased from the low load level (Lo) to a high final value (Lh), where Lh was different for each specimen and it was maintained constant for long time. The temporal behavior of the recorded PSC show that during the load increase a spike-like PSC emission was recorded and consequently a relaxation of the PSC, after reaching its final value, follows. The relaxation process of the PSC was studied using non-extensive statistical physics (NESP) based on Tsallis entropy equation. The behavior of the Tsallis q parameter was studied in relaxation PSCs in order to investigate its potential use as an index for monitoring the crack evolution process with a potential use in non-destructive laboratory testing of cement-based specimens of unknown internal damage level.The dependence of the q-parameter on the Lh (when Lh<0.8Lf), where Lf represents the 3PB strength of the specimen, shows an increase on the q value when the specimens are subjected to gradually higher bending loadings and reaches a maximum value close to 1.4 when the applied Lh becomes higher than 0.8Lf. While the applied Lh becomes higher than 0.9Lf the value of the q-parameter gradually decreases. This analysis of the experimental data manifests that the value of the entropic index q obtains a characteristic decrease while reaching the ultimate strength of the specimen, and thus could be used as a forerunner of the expected failure.

Computer Nonlinear Analysis of the Formation and Development of Cracks in a Travertine Stone Pavement Exposed to Bending Stress Caused by a Single Load

This paper focuses on a computer nonlinear analysis of the formation and development of cracks in a travertine stone pavement. The causes of cracking in the upper travertine layer of the tested multi-layer floor are modeled and investigated by a computer nonlinear static analysis. The paper illustrates the setting of material characteristics of the stone in the design of the material model according to the performed destructive and non-destructive laboratory tests.

Finite element analysis for the evaluation of the structural behaviour, of a prosthesis for trans-tibial amputees

The finite element analysis (FEA) has been identified as a useful tool for the stress and strain behaviour determination in lower limb prosthetics. The residual limb and prosthetic socket interface was the main subject of interest in previous studies. This paper focuses on the finite element analysis for the evaluation of structural behaviour of the Sure-flex™ prosthetic foot and other load-bearing components. A prosthetic socket was not included in the FEA. An approach for the finite element modelling including foot analysis, reverse engineering and material property testing was used. The foot analysis incorporated ground reaction forces measurement, motion analysis and strain gauge analysis. For the material model determination, non-destructive laboratory testing and its FE simulation was used. A new, realistic way of load application is presented along with a detailed investigation of stress distribution in the load-bearing components of the prosthesis. A novel approach for numerical and experimental agreement determination was introduced. This showed differences in the strain on the pylon between the experimental and the numerical model within 30% for the anteroposterior bending and up to 25% for the compression. The highest von Mises stresses were found on the foot–pylon connecting component at toe off. Peak stress of 216 MPa occurred on the posterior adjusting screw and maximum stress of 156 MPa was found at the neck of the male pyramid.

Practical Method to Understand the Effect of Aggregate Drying on the Moisture Content of Hot-Mix Asphalt

The drying of aggregates is a critical step in obtaining moisture-free hotmix asphalt (HMA). The drying depends on many factors, which include the absorption and the moisture content of the aggregates as well as the drying temperature and time. The effect of drying of the aggregates on the moisture content of the resultant HMA needs to be understood so that adequate drying can be carried out for mixes, such as warm-mix asphalt (WMA), which are produced at lower than conventional temperatures. The objectives of this study were (a) to develop a laboratory method to produce HMA samples with various moisture contents that mimic insufficient drying of aggregates in a drum mixer and (b) to develop a nondestructive laboratory testing procedure to determine moisture content of compacted HMA samples. Aggregates with relatively high and low absorption rates were selected. A practical method was developed to mimic the retention of aggregate moisture in HMA in the laboratory. Good correlation was obtained between drying time and moisture-content loss for the aggregates of high and low water absorption. An experiment with heat transfer and a simulation with a finite element method confirmed the presence of moisture and its significant effect on the thermal conductivity of the mixes, which provided a nondestructive approach to determine moisture content of compacted HMA samples.

The use of direct measurement of ankle kinetics in the calculation of energy storage and return in a dynamic elastic response prosthesis

The finite element analysis (FEA) has been identified as a useful tool for the stress and strain behaviour determination in lower limb prosthetics. The residual limb and prosthetic socket interface was the main subject of interest in previous studies. This paper focuses on the finite element analysis for the evaluation of structural behaviour of the Sure-flex™ prosthetic foot and other load-bearing components. A prosthetic socket was not included in the FEA. An approach for the finite element modelling including foot analysis, reverse engineering and material property testing was used. The foot analysis incorporated ground reaction forces measurement, motion analysis and strain gauge analysis. For the material model determination, non-destructive laboratory testing and its FE simulation was used. A new, realistic way of load application is presented along with a detailed investigation of stress distribution in the load-bearing components of the prosthesis. A novel approach for numerical and experimental agreement determination was introduced. This showed differences in the strain on the pylon between the experimental and the numerical model within 30% for the anteroposterior bending and up to 25% for the compression. The highest von Mises stresses were found on the foot–pylon connecting component at toe off. Peak stress of 216 MPa occurred on the posterior adjusting screw and maximum stress of 156 MPa was found at the neck of the male pyramid.