The Opportunity of Modern High-Toughness Technical Ceramics for Undersea Systems

A confluence of recent developments in the formulation and processing of technical ceramics enables an important opportunity for submersible designers, namely, the reliable use of ceramics having density of near 3 g/cm3, compression strength of >4 GPa, tensile strength of >690 MPa, and fracture toughness (KIc) of 8‐10 MPa-m1/2. Concurrent developments in high-strength brazing of ferrous and nickel-based metals to these tough ceramics enables the integration of pressure envelopes with removable endcaps or ports, as well as optimum stiffener configurations and other internal or external design features. The specific opportunity presented by this confluence of tough ceramics and brazed metallic fittings is the possibility of full-ocean-depth (>6,000 m) dry submersible structures with weight/displacement (W/D) ratio < 0.7, as compared to W/D > 1.0 for metallic structures. Self-buoyant dry hull structures at these depths will greatly expand submersible design options, minimizing the need for full-ocean-depth syntactic foams to float key functionalities. The processing of these ceramics requires a cold isostatic press (CIP) or slip cast “green forming” step, plus sintering to near full density, followed by hot isostatic press (HIP) to final density. Present HIP facilities can support processing of 81-cm diameter × 190-cm-long ceramic vessels and brazing of ceramic/metal assemblies to ~163-cm diameter × 254-cm-long in the United States. If larger ceramic pressure hull components are desired, a “tiled” ceramic structure can be assembled and brazed or bonded together with thin metallic skins in a sandwich structure.

COPING MANUFACTURED TECHNIQUE OF SPINELL SLIP CAST ALL CERAMIC BY CONVENTIONAL METHODS AND CAD/CAM

Background: Ceramic restorations is divided into two kindsnamelyPorcelain Fused to Metal (PFM) and all-ceramic restorations. In ceram spinell is one of the materials needed for manufacturing anterior coping of all ceramic which has better aesthetic than in other in ceram. Methods which have been done are Conventional Slip Cast by application of spinell paste on refractory die manually and CAD/CAM computer-based technique. The difference of mentioned previously methods is few step-in slips cast methods can be performed only by one step CAD/CAM methods. Objective: To discover the differences between Conventional Slip Cast methods and CAD/ CAM methods. Review: Application of CAD/CAM methods has few advantages compared to conventional methods. Since few step-in conventional methods can be performed only one step in CAD/CAM methods. Conclusion: In order to shorten the time in manufacturing spinell all-ceramic, the dental technician may use CAD/CAM methods. Few advantages of CAD/CAM methods compare to slip cast methods are not necessary to do die to block out, die duplication, wetting agent spraying, vitasonic and ultrasonic usage, giving border by ink pen for determining application border, preparing spinell paste for coping application. Those steps all can be performed only by scanning, design, and milling by CAD/CAM methods. Besides that, coping result produced by CAD/ CAM methods has good accuracy due to spinell block utilization which has better homogenous composition.

Dynamic modeling of the turning process of slip-cast fused silica ceramics using the discrete element method

Simulation of brittle regime machining of materials (such as ceramics) is often difficult because of the complex material removal mechanisms involved. In this study, the discrete element method is used to simulate the dynamic process for machining of slip-cast fused silica ceramics. Flat-joint contact model is exploited to model contacts between particles in synthetic discrete element method models. This contact model is suitable for modeling of brittle materials with high ratios (higher than 10) of unconfined compressive strength to tensile strength. The discrete element method has the ability to simulate initiation, propagation, and coalescence of cracks leading to chip formation in the brittle regime of cutting. Applying the discrete element method, the influences of operating conditions on the creation of surface/subsurface damages, chip formation, and cutting forces are studied. It is shown that the parameters of the material model determined from conventional calibration tests do not provide quantitatively accurate prediction of cutting forces. As such, model updating is carried out using the forces obtained in the cutting experiments, and the numerical results are verified against experimental cutting forces. The differences between experimental and numerical machining forces are in the range of 10%–30%. Finally, the results of discrete element method simulations reveal that the nature of micro-crack propagation is brittle in the machining process of ceramics.