The goal of this work is to quantitatively examine the effect of adhesive resin cement on the probability of crack initiation from the internal surface of ceramic dental restorations. The possible crack bridging mechanism and residual stress effect of the resin cement on the ceramic surface are examined. Based on the fracture-mechanics-based failure probability model, we predict the failure probability of glass-ceramic disks bonded to simulated dentin subjected to indentation loads. The theoretical predictions match experimental data suggesting that both resin bridging and shrinkage plays an important role and need to be considered for accurate prognostics to occur.
As a standard test-bar permanent mold, the ''Stahl'' Mold has been widely used in foundries to assess the properties of cast alloys. However, inferior mechanical properties are often obtained with this mold due to shrinkage-induced microporosity in the gage section. In order to improve the mechanical properties, a design modification comprising a thin knife ingate between the feeder and test-bar cavity was evaluated in this work. The new design was studied by computeraided simulation. Simulations predicted that the knife ingate improved the metal feeding capability and reduced the shrinkage microporosity at the gage section from 3 to 1 pct. Experimental verification work has been undertaken with aluminum alloy A356, and the results were analyzed by a statistics theory-based factorial analysis method. The new design resulted in main effects with ultimate tensile strength (UTS) improvement of 20 MPa (relative 12 pct) and elongation increment of 2 pct (relative 45 pct) for the as-cast test bars.
Hole enlargement while drilling (HEWD) is now widely used in deepwater applications. It provides reduced-clearance casing programs, improves drilling in swelling formations, and helps equivalent circulating density (ECD) management. HEWD applications commonly use an underreamer in a BHA with a rotary steerable system (RSS). Currently, traditional reamer placement results in a long portion of unenlarged hole—rathole—which requires an extra trip to enlarge. A new BHA design is being sought to eliminate the second trip requirement—the objective is to find a feasible solution. Placing the reamer closer to the bit would forgo the need for a second trip; however, the placement of a traditional reamer is limited by its design. In response to such limitation, a solution is proposed to design a rathole elimination (RHE) BHA which includes a lower reamer placed between MWD/LWD tools and the RSS. During HEWD, the lower reamer is in passive (off) mode while a traditional reamer is active. Upon reaching TD, the BHA is tripped back to position the lower reamer above the rathole and is then activated to enlarge the rathole. This RHE BHA design thereby eliminates the second trip requirement. This paper discusses the operational learnings and drilling performance of the proposed RHE BHA design. A field test in Texas is presented and documents the downhole dynamic performance of the single-trip BHA. Drilling dynamics measurement modules (DDMM) were positioned near the reamers to measure the downhole drilling dynamics. This run captured data for traditional HEWD operations and rathole elimination operations. To ensure stable drilling operations, a time-based dynamic simulation perfomed a prerun parametric sensitivity study to help identify the optimal parameters that could deliver high ROP, low vibration, and low stick-slip. A roadmap was made for operational guidelines based on simulation analysis. The test was successfully completed with stable HEWD and RHE operations observed. After completion of the run analysis of the DDMMs, measured downhole dynamic data showed stable downhole drilling dynamics during both HEWD and RHE operations. The RHE operation generated similar levels of vibration and stick-slip at the reamer and MWD/LWD tools compared with the HEWD operation. This field test shows that a single-BHA design can deliver stable drilling dynamics in both HEWD and RHE operations, and demonstrates the capability of the solution in eliminating the second trip requirement. This single-trip RHE BHA design will not only reduce operational costs, but will also lower HSE risk by enabling less BHA handling on the rig floor.
Downhole vibration is detrimental to drilling efficiency and can cause MWD/LWD tool failure, drillstring fatigue, bit/PDM damage. Preventing or mitigating BHA instability is critical to improve drilling efficiency, increase ROP and reduce drilling costs. To prevent dynamic instability requires an in-depth understanding of the BHA's downhole behavior in terms of the actual phenomenon and ability to determine root cause. Downhole RPM and vibration data sent to surface from MWD/LWD usually have very low frequency limited by telemetry. Because vibrations are measured at a distance from the bit, the data may not capture detailed bit behavior patterns. The low frequency data is typically used in combination with steady-state response or static analysis models developed to predict interaction between the drillstring and wellbore. Results produced by these type systems have been less than optimal. To obtain superior quality downhole vibration data, a high-frequency drilling dynamics measurement module (DDMM) was recently developed to capture and measure bit/BHA dynamic response. The authors will describe the application of the new module to measure and record downhole RPM, acceleration at bit/BHA at sampling frequencies up to 2048-Hz. Analysis verified the high-frequency data produces more specific details about dynamic behavior compared to standard data. The module can be positioned at any location within the BHA or directly above the bit. The high-frequency data is used in conjunction with a unique time-based dynamic simulation system to verify and confirm the modeling's prediction of ROP/RPM, acceleration and drillstring instability including stick-slip/whirl. When drilling dysfunction is observed, the time-based modeling system has the potential to ascertain the root cause not typically identified in measured data. This system approach is cost effective and can be highly effective at preventing or mitigating complex instability issues. Three DDMM field tests are presented that document the capability of the combined testing and modeling system approach to achieve better understanding of downhole dynamics: Case Study 1 Rotary BHA with one DDMM positioned at top of bit. Analysis of actual downhole data from DDMM shows large RPM variation at the bit which was confirmed by the time-based modeling system. The two data plots showed good correlation between axial/lateral acceleration (acceleration/g's vs time/sec). Case Study 2 Motor BHA with two DDMMs installed. One positioned at top of motor another at top of the bit. Analysis of actual data documents stick-slip at the bit and top of motor which is confirmed by the modeling system. Detailed analysis of the two data plots revealed good correlation between actual and modeled data with both depicting negative RPM at the top of the motor with increased acceleration at the occurrence of stick-slip (RPM vs time/sec). Case Study 3 Motor BHA with two DDMMs installed. One positioned at top of motor, another at top of bit. Analysis of actual data documents stick slip at the top of motor which was confirmed by the modeling system. Further analysis of the modeling data plot identified stick-slip coupled with BHA whirl. The case studies document accurate modeling predictions of ROP/RPM and acceleration corroborated by the measured data. Modeling also successfully predicted dynamic instability issues identified by actual DDMM measurement and gave specific details about coupling of stick-slip and BHA whirl not observed in the measured data.
This work is a case study of applying Bayesian analysis, a statistical data method, in the design optimization of permanent test-bar mold. The permanent test-bar mold is used in casting foundry to examine the metal quality. Since the current standard test-bar mold suffers from shrinkage porosity which detracts from best properties, a modified design is recently proposed to improve the mechanical properties. In order to validate the new design, Bayesian data analysis method is utilized to analyze the experimental data from the two designs. The effects of the mold designs and casting process operational parameters on the mechanical properties of castings are compared. Main effect to the mechanical properties is identified based on the Bayesian analysis.
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