Effect of Polymer Liners in Different Via Shapes: Impact on Crosstalk Induced Delay

The performance of a through silicon via (TSV) based 3D integrated circuit technology is primarily dependent on the choice of an appropriate liner material. The most commonly used liner material SiO2 is undergoing considerable reliability challenges such as coefficient of thermal expansion (CTE) mismatch, scallop formation, and interfacial delamination related problems. Therefore, TSVs employed with a polymer liner have achieved significant attention in recent years due to their low dielectric constant and excellent step coverage along the via surface that can effectively reduce thermal stress and crosstalk induced delay. This paper presents a comprehensive and accurate RLGC model for different via shapes considering the impact of various liner materials on the crosstalk induced delay. Considering an accurate via geometry and material properties at 32 nm and 45 nm technology, the proposed equivalent RLGC parameters include the cumulative effects of TSV metal, liner, bump, and the silicon substrate. The aforementioned parameters are used to model a novel T-type equivalent electrical network of cylindrical, tapered, and coaxial TSVs considering a coupled driver-via-load (DVL) setup. The proposed equivalent models of different via shapes are used to demonstrate the worst-case crosstalk induced delay in TSVs under the influence of various liner materials. Considering a tapered TSV, a significant improvement in crosstalk induced delay at 32 nm w.r.t. 45 nm technology is observed as 53.5%, 33.76%, and 19.12% at aspect ratios of 2.4, 3, and 4, respectively for the BCB liner.

Fretting and corrosion of metal liners from modular dual mobility constructs

Aims Dual mobility implants in total hip arthroplasty are designed to increase the functional head size, thus decreasing the potential for dislocation. Modular dual mobility (MDM) implants incorporate a metal liner (e.g. cobalt-chromium alloy) in a metal shell (e.g. titanium alloy), raising concern for mechanically assisted crevice corrosion at the modular liner-shell connection. We sought to examine fretting and corrosion on MDM liners, to analyze the corrosion products, and to examine histologically the periprosthetic tissues. Methods A total of 60 retrieved liners were subjectively scored for fretting and corrosion. The corrosion products from the three most severely corroded implants were removed from the implant surface, imaged using scanning electron microscopy, and analyzed using Fourier-transform infrared spectroscopy. Results Fretting was present on 88% (53/60) of the retrieved liners, and corrosion was present on 97% (58/60). Fretting was most often found on the lip of the taper at the transition between the lip and the dome regions. Macrophages and particles reflecting an innate inflammatory reaction to corrosion debris were noted in six of the 48 cases for which periprosthetic tissues were examined, and all were associated with retrieved components that had high corrosion scores. Conclusion Our results show that corrosion occurs at the interface between MDM liners and shells and that it can be associated with reactions in the local tissues, suggesting continued concern that this problem may become clinically important with longer-term use of these implants. Cite this article: Bone Joint J 2021;103-B(7):1238–1246.

Adverse reaction to metal debris due to fretting corrosion between the acetabular components of modular dual-mobility constructs in total hip replacement: a systematic review and meta-analysis

Modular dual-mobility (MDM) constructs can be used to reduce dislocation rates after total hip replacement (THR). However, there are concerns about adverse reaction to metal debris (ARMD) as a result of fretting corrosion between the metal liner and shell. This systematic review reports outcomes following THR using MDM components. It was registered with PROSPERO and conducted in line with Cochrane and PRISMA recommendations. Sixteen articles were included overall, with meta-analysis performed on relevant subsets using a random intercept logistic regression model. Estimated median incidence of ARMD requiring revision surgery within study follow-up period was 0.3% (95% CI 0.1 – 1.8%, from 11 cohort studies containing 1312 cases). Serum metal ion levels were mildly raised in 7.9% of cases, and significantly raised in 1.8%, but there was no correlation with worse clinical hip function scores within studies. Dislocation rate was 0.8%. Revision rate was 3.3%. There are mixed reports of wear on the backside of the metal liner from the acetabular shell and screw heads. Both implant design and component malseating are implicated, but currently it is unclear to what extent each factor is responsible. Studies were poor quality with high risk of confounding, especially from trunnion corrosion. We have made recommendations for further work. In the meantime, surgeons should be aware of the potential risk of ARMD when considering using an MDM prosthesis, and, if selecting one, must ensure proper seating of the liner and screws intraoperatively. Cite this article: EFORT Open Rev 2021;6:343-353. DOI: 10.1302/2058-5241.6.200146

Mechanical Study of Carbon Fiber Reinforced Plastic and Thin-walled Metal Liner in Bi-Material COPV Based on Grid Theory Optimization

Composite over-wrapped pressure vessel (COPV) with ultra-thin metal liner and high strength carbon fiber reinforced plastic (CFRP) structure was widely used in space system. Meanwhile, there are some difficulties in the calculation of COPV stress-strain state related to the elastic-plastic liner and elastic composite. In this paper a novel design theory was proposed for calculating stress distribution in the bi-material COPV and determining the optimal thickness parameters of COPV based on traditional grid theory optimization. This new theory named Parameters Correspondence Relationship Structure Design Method (PCRSDM) can increase the design precision and structure performance factor of COPV compared to traditional grid theory. The correct models of mechanical characteristic between liner and CFRP are established from the view of optimized grid theory, the present theory is useful to develop a theoretical framework to calculate and design the COPV double shells. The COPV stress-strain behavior is also systemically studied by the ANSYS finite element analysis (FEA), the results show good agreement between FEA simulation and PCRSDM calculation. Both FEA and PCRSDM can meet the design requirements of COPV. A complete design, development and qualification testing of a specialized COPV used to satellite propulsion system was successfully conducted to verify the COPV design in terms of PCRSDM and FEA, the result show that PCRSDM is suitable for the design of COPV.

Buckling analysis of thin-walled metal liner of cylindrical composite overwrapped pressure vessels with depressions after autofrettage processing

The cylindrical filament wound composite overwrapped pressure vessels (COPV) with metal liner has been widely used in spaceflight due to their high strength and low weight. After the autofrettage process, the plastic deformation of the metal liner is constrained by composite winding layers, which introduce depressions to the metal liner that causes local buckling. To predict the local buckling of the inner liner with depressions of the pressure vessel after the autofrettage process, a local buckling analysis method for the metal liner of COPV was developed in this article. The finite element method is used to calculate the overall stress distribution in the pressure vessel before and after the autofrettage process, and the influence of local depressions on the buckling is evaluated. The axial buckling of the pressure vessel under external pressure is analyzed. The control equation of the metal liner with depressions is developed, considering the changes in the pressure and the bending moment of the liner depressions and its vicinity during the loading and unloading process. Taking the cylindrical COPV (38 L) with aluminum alloy liner as an example, the effects of liner thickness, liner radius, the thickness-to-diameter ratio, autofrettage pressure, and the length of straight section on the autofrettage process are discussed. The results show that the thickness of the inner liner has the most significant influence on the buckling of the liner, followed by the length of the straight section and the radius of the inner liner, while the autofrettage pressure has the least influence.

Experimental Evaluation of Using Silica Aerogels as the Thermal Insulator for Combustor Liners

An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated IR camera. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates. The measured evolution of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. Improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.

A Multi-Timescale Approach for the Prediction of Temperatures in a Gas Turbine Combustor Liner

The desire for increased engine efficiencies is driving higher firing temperatures. But this increases the risk for hot spots in solid components which can lead to durability issues. These may not be discovered until late in the design process through expensive and time consuming thermal paint tests. Historically, conjugate heat transfer simulations to predict solid temperatures have been done with steady RANS. However, Large Eddy Simulation (LES) is now being used in the early design process for gas turbine engines to account for the multiphysics of reacting flows. Incorporating the solid into these simulations poses a new challenge: the physical response time of the solid components can be orders of magnitude larger than the reacting gas phase. Running a fully coupled unsteady conjugate heat transfer analysis is therefore not tractable, but the high fidelity of the LES reacting solution is still desired. The objective of this paper is to demonstrate a multi-timescale simulation approach for conjugate heat transfer (CHT) in Simcenter STAR-CCM+ 2019.3. The combustor is solved using LES, including all relevant physics, while steady state conduction is determined in the metal liner and thermal barrier coating. Time averaged boundary conditions are transferred from the combustor to the solids, and temperature is returned through multiple exchanges until the solid temperatures reach a stable solution. A simplified case is used to verify the approach, and then results from a test combustor are compared against data. The investigation compares results obtained with PISO and SIMPLE numerical schemes.