Temperature Dependence of Fracture Characteristics of Variously Heat-Treated Grades of Ultra-High-Strength Steel: Experimental and Modelling

The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨−196; 22⟩ °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson.

Ductility of Concrete Beams Reinforced with FRP Rebars

Concrete beams reinforced with FRP rebars have greater durability than standard steel reinforced elements. The main disadvantage of using FRP rebars is the low ductility of elements which may be unacceptable in certain situations. There are several different ways of increasing the ductility of concrete elements, which are analyzed in this paper. They are compared based on efficiency, influence on durability and ease of construction. Less analyzed and tested methods are given more attention to try and expand the current knowledge and possibilities. For methods that lack experimental data, theoretical analysis is undertaken to assess the possible influence of that method on the increase in ductility. Ductility was obtained by calculating bending moment–curvature diagrams of cross sections for different reinforcement layouts. One method that lacks experimental data is confining the compressive area of beams with tensile FRP reinforcement. Theoretical analysis showed that confining the compressive area of concrete can significantly increase the ductility and bending capacity of beams. Since experimental data of beams reinforced with FRP rebars in tension and confined compressive area is sparse, some suggestions on the possible test setups are given to validate this theoretical analysis. Concrete beams reinforced with FRP can be detailed in such a way that they have sufficient ductility, but additional experimental research is needed.

Composite Shaftless Roller Design for Conveyor System

Improving the performance of idlers is paramount to the performance of the conveyor system in various industries since belt conveyors can be many kilometers in length and consequently there are a huge number of rollers in use. The key intention of this work is the development of a light-weight composite idler roller. Critical design considerations are strength-to-weight ratio and performance. Most importantly, the design must reduce the weight of the roller as compared to standard steel rollers. The final design provides a significant reduction in weight of about 47 % over that of traditional steel rollers of a similar size.

In Vitro Comparison of Root Surface Treatment Effect between Root Scaling with Ultrasonic Inserts and Gracey Curette and Polishing with Different Cleaning Pastes

The aim of this study was the morphological evaluation of root surfaces subjected to manual (curette) and ultrasonic (conventional and diamond tips) scaling. The surface was then polished with a rubber cup and three medium-sized pastes. Ninety teeth were randomly divided into three groups of 30 and subjected to three different root instrumentation: (1) manual instrumentation with a Gracey® curette; (2) ultrasonic instrumentation with a standard steel tip (Universal Perio S-SERIES: USU, Hu-Friedy, Chicago, IL, USA) at a power equal to 50%; and (3) with a diamond tip (Punta Piezo Serie E Scaling, Hu-Friedy, Chicago, IL, USA) at a power of 20%. Each group of the instrumented teeth was then divided in three subgroups of 10 and subjected to 30 s of rubber polishing with three different polishing pastes with medium grain sizes in single-dose cups: (1) Ultrapro Tx cool mint medium®; (2) Stomyprox media®; and (3) Nupro medium orange®. Polyether root surface replicas were then taken from all 90 samples and analyzed by SEM to evaluate surface morphology after scaling and polishing procedures. All scaling techniques caused an alteration of the root surface without statistically significant difference, whereas polishing resulted in maintenance or improvement of the surface texture.

Feasibility Analysis of Bolted Joints with Composite Fibre-Reinforced Thermoplastics

The use of composite materials has shown steady growth in recent years due to their excellent specific mechanical properties and the possibility to reduce the weight of vehicles without impairing their safety and comfort. Continuous fibre-reinforced thermoplastic composites (CFRTP) show dynamic, acoustic, and damping properties far superior to steel and can be recycled and repaired. Their excellent properties make CFRTP good candidates for anti-vibration and shock absorbing components, however, out-of-plane mechanical properties hinder the anchoring to the vehicle’s body by means of bolted connections. The results obtained in this study show how the maximum torque that can be applied without cracks or breakage phenomena is lower than in standard steel joints. Although the preload’s value is admissible, this one is reduced over time due to relaxation phenomena associated with the viscoelastic behaviour of thermoplastic matrix. The results obtained can be improved with the integration of metal inserts in connections’ areas. In this study, a case study of a gear mount replacing the steel core with CFRTP reinforced with inserts is carried out. The results show a reduction above 50% in weight, opening the possibility of lighter structures in the automotive sector.

Corrosion Behavior of L245N Standard Steel in CO2 Saturated Brine under Flow Condition

The corrosion behavior of oilfield used L245N standard steel was tested in simulated oilfield solution by dynamic high-temperature autoclave. The corrosion products were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Electrochemical impedance spectroscopy (EIS) respectively. In addition, the corrosion rates and surface morphological characteristics of the steels after different exposure times were studied. The results showed that the corrosion rate decreased sharply and then increased with time in the high salinity flow solution, which was related to the formation of corrosion scale and the remaining cementite within it. At the beginning of the exposure time, the formed corrosion scale became thicker, resulting in a significant decrease of the corrosion rate. While with increasing time, on the one hand, the increased remaining cementite within corrosion scale facilitated the corrosion by the galvanic corrosion between the remaining cementite and the ferrite within the metal. On the other hand, the protective effect of corrosion scale formed on the remaining cementite skeleton declined due to the formation of large amounts of FexCa1−xCO3, which also promoted the corrosion rate of the steels, both these ways contributed to a slow increase of corrosion rate.

In Silico Analysis of Elastomer-Coated Cerclage for Reducing Sternal Cut-Through in High-Risk Patients

Background: AISI 316L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to post-operative complications. A biocompatible elastomer (Pellethane®) coating on the standard wire is proposed to mitigate the cut-through effect. Methods: Simplified peri-sternal and trans-sternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 to 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. Results: It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the trans-sternal contacts in comparison to peri-sternal contacts. Conclusions: Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane® will majorly address the cut-through complication.

Scientific Rationale for the Movable Pipeline Technology for Transporting CNG by Sea

A new efficient CNG module design for the transportation of natural gas by sea is proposed and substantiated. A mathematical model for determining the technical and economic parameters of a movable pipeline module, which is designed for transporting natural gas in a compressed state and consists of a frame structure, the dimensions of which correspond to the 40-foot marine container size and a pipe coil is described. To facilitate construction, it is proposed that a large portion of the coil be made in the form of a two-layer composite construction. The inner layer consists of standard steel tubes or adapters, and the outer layer is fiberglass wound on them. On the basis of the mathematical model an algorithm and a program were compiled, which allowed to determine the technical and economic parameters of the movable pipeline module. The results obtained for the Caspian region are analyzed.