Minimum Thickness Requirements Research Articles

Classification system for maxillary fixed dental prostheses.

To present an addendum to existing fixed dental prostheses (FDPs) classification system for maxillary prostheses. The new classification identifies the relationships between FP-1 (fixed prostheses) designs and newly developed clinical interdental gingival contours. Clinical and laboratory descriptions of the various types of full-arch fixed prostheses are described with photographic illustrations. Benefits and limitations of the various prosthetic designs are explained. Surgical differences in the amount of alveolectomy are illustrated. One clinical case is demonstrated. A new classification system for maxillary implant fixed complete dentures is presented. The new system will serve as an improved communication aid for clinicians, patients, and laboratory technicians. Treatment of patients with edentulous maxillae and/or terminal dentitions and implant fixed complete dentures include several options relative to design and materials. Restorative space can have a major impact on prosthesis design and longevity. Early on in dental implant therapy, prostheses were generally made with cast metal frameworks, denture bases and denture teeth. Prosthetic complications were widely reported. With increased clinical experience and improved materials, computer-aided design and computer-aided manufacturing (CAD-CAM) protocols were developed that allowed stronger prostheses to be constructed in reduced or small restorative volumes. FP-1 ceramic implant-supported fixed prostheses (CISFPs) are designed to replace only the dental hard tissues and to promote preservation and rehabilitation of gingival soft tissues. The physical properties and minimum thickness requirements in full arch prostheses are influenced by several factors including distances between implants and rigid connector sizes. FP-1 CISFPs may be the closest prostheses the profession can offer edentulous patients that mimic the look, feel, and function of missing dentitions. Aesthetic outcomes of FP-1 CISFPs are variable and depend on a multitude of factors. This article presented a classification system that builds on existing classification by identifying the level of papilla heights achieved with FP-1 CISFPs.

On criteria of minimum thickness of plating for ships in composite materials

The paper discusses the selection of the minimum thickness of the plating for ships made of composite materials. The reasons for restrictions are considered as the prevention of filtration and protection from contact damage. It has been established that there are two fundamental approaches: the actual thickness and the mass of the reinforcement. With the examples of ship accidents, the limitations of existing approaches to minimum thickness requirements are considered. The practice of classification societies on thickness regulation is analyzed, the approaches and the resulting thicknesses of bottom and side shells are compared, and also the ratio of inner and outer skin thicknesses. The influence of exceeding the minimum thicknesses is noted on the example of the interceptor boat project. For Russian classification societies, proposals have been formulated to improve the requirements.

Probabilistic assessment of ACI 318 minimum thickness requirements for two-way slabs

ABSTRACT Following the ACI 318 design code and to control deflections, structural engineers must adhere to minimum thickness requirements for reinforced concrete (RC) slabs. However, these requirements do not account for various influencing variables such as span length, aspect ratio and applied live load. This paper assesses the adequacy of the ACI 318 minimum thickness requirements for two-way RC slabs through a probabilistic approach using Monte Carlo simulation (MCS). The probability distribution of the span-to-depth ratio (SDR) was fitted to the Burr distribution, and the goodness-of-fit test was applied to assess the fitting. Then, the effect of span length, aspect ratio, and live load on the maximum allowable SDR was evaluated, considering all material properties and applied loads as random variables. The analyses have shown a high correlation between the studied variables and the SDR. Therefore, multiple regression analysis was carried out, and four prediction models were proposed to conservatively predict the SDR for two-way slabs. The accuracy of the prediction models was statistically tested by comparing calculated to predicted SDR values, and a 10% maximum relative error was exhibited. The proposed prediction models were accurate for all practical ranges of span length, aspect ratio and live load in two-way slabs.

In-Situ Resistance Optimization for ALD Nanocomposite Resistive Materials

Atomic layer deposition (ALD) made resistive nanocomposite materials can be used in many emerging applications such as charge draining layers for electron optic and MEMS devices, functional resistive layers in electron/ion amplifying microchannel plates (MCPs) which are used in photodetectors and mass spectrometry, HF resistance with tunable electrical conductivity coatings for stabilizing Li-ion battery cathode materials, selective solar absorbing coatings for concentrated solar power (CSP), and barrier and encapsulation coatings. Over the last decade, we have worked broadly on the research and development of resistive nanocomposite coatings. In this context, we have developed many nanocomposite materials with tunable resistance based on mixing conducting ALD metal and insulating ALD metal oxide or metal fluoride processes. These ALD nanocomposite materials show robust material performance in many of the applications listed above. Here we are particularly targeting a functional resistive coating that now commercially used for manufacturing large area ALD-MCPs. For this, there are two key topics that we are addressing a) Minimum thickness requirement for resistive coating which provides a stable targeted resistance behavior for MCPs, and b) Can we tune the temperature coefficient of resistance (TCR) of the ALD nanocomposite materials so that the ALD MCPs can operate over a wide temperature range without affecting their performance. To address these two topics, we have utilized in-situ resistance monitoring during the ALD nanocomposite process. With this method we have optimized resistive nanocomposite material ALD processes e.g. (M:Al2O3 where M= W and Mo) for MCPs and also targeted the desired TCR of the materials and achieved ultra-low TCR values. We believe these optimized coatings will reduce the ALD-MCP processing time substantially and enable ALD-MCPs and photodetectors to operate over a broader temperature range compared to existing ALD-MCPs.

Reliability-based inspection and maintenance planning of a nuclear feeder piping system

Inspection and maintenance (I&M) is essential to ensure the integrity of feeder pipes, which are parts of the primary heat transport system in a nuclear power plant. The pipes are subject to flow accelerated corrosion (FAC), which can compromise the integrity of the piping system and lead to high repair costs. We explore the opportunity for improving I&M strategies while ensuring that the system still maintains an acceptable level of reliability. To this aim, a reliability-based planning framework is proposed, in which every pipe in the system meets the minimum thickness requirement at a specified annual probability. With this planning framework we can a) evaluate the performance of any I&M strategy constrained to a fixed reliability criterion, without requiring this strategy to be specifically designed for such a criterion; and b) find an I&M strategy optimized for this reliability level using a heuristic description of the strategy space. We demonstrate the framework with a case study, where the wall thinning due to FAC is modeled as a Gamma process with uncertain parameters. We compare the expected life-cycle cost of multiple strategies for I&M of a feeder system with 480 pipes. The proposed approach is compared with an I&M strategy currently used by the industry, which highlights the efficiency of the proposed optimization method.

Limit-state analysis of parabolic arches subjected to inertial loading in different gravitational fields using a variational formulation

For thousands of years, arches have been used as durable structures that are easy to build and that rely on gravity for their inherent stability. Since then, many researchers and engineers have studied their stability either when subjected to gravity or inertial loading. Currently, given the Insight mission to Mars and the ambitious Artemis program to the Moon, it has become apparent that there will soon be the need to design and build the first resilient extraterrestrial structures and arches represent an ideal option for such structures. This paper focuses on the stability of parabolic arches with different embrace angles subjected to different levels of equivalent inertial loading in low-gravity conditions. The results are contrasted with the well-studied circular arches. More specifically, this investigation employs variational principles to identify the imminent mechanisms and numerical methods based on the limit thrust line concept in order to estimate the minimum required thickness of parabolic arches for a given loading and in different gravitational fields. The paper shows that although parabolic arches can be much more efficient than their circular counterparts for gravitational-only loading, this is not the case for different combinations of inertial loading and embrace angles where the opposite can be true. It highlights the dominant effect of low-gravity conditions on the minimum thickness requirements for both types of arches and considers the effect of a potential additional infill for radiation shielding. Furthermore, this study reveals a self-similar behaviour, introduces a “universal” inertial loading and showcases, through the use of master curves, the areas where the parabolic arches are more efficient than their circular counterparts and those where the opposite is true. These areas can be used for the preliminary design of such structures. Additionally, the paper identifies hidden patterns associated with the developed mechanisms between the two different geometries for the different gravitational fields. Finally, it presents a case study where the need to optimise the structural form of extraterrestrial structures becomes evident.

Out-of-plane constraint loss in three point bend specimens with notches

This paper presents an experimental and numerical study of the effect of specimen thickness on the effective notch toughness Kmatρ for cleavage fracture measured using Single Edge Notch Bend (SENB) specimens containing a U-notch instead of a fatigue pre-crack. These specimens are typically used to measure a material's effective notch toughness Kmatρ and to assess failure of a structure containing a non-sharp defect using the Notch Failure Assessment Diagram (NFAD). Both the experimental data and the Finite Element (FE) failure predictions show a significant influence of specimen thickness on Kmatρ, over and above the microstructural weakest link effect arising from differences in the volume of the plastic zone. Kmatρ is a function of not only the in-plane effect of the notch radius, but also an out-of-plane constraint loss which itself is enhanced by the presence of the notch radius. Significant out-of-plane constraint loss occurred for notched specimens with a ratio of thickness B to width W of 0.5, a geometry that if pre-cracked would have met the minimum thickness requirement mandated by ASTM E1820. Doubling the thickness to B/W = 1.0 was sufficient to eliminate the out-of-plane constraint loss. The use of experimentally measured Kmatρ values in an NFAD assessment of a structure may therefore be non-conservative if B/W<1.0.

Analysis of buried pipelines laid under the pipelines operation, is subjected to operational loads

Today’s successful operation within the oil and gas industry is based on the triangle “Safety – Reliability – Profitability (Efficiency)”. It is of high importance to properly balance these different and sometimes opposite positions. The article describes the characteristics of the strength of the buried offshore pipeline. Pipe geometric imperfections as the cross section ovality, combined load effects as axial and bending loads superimposed to the external pressure, material properties as compressive yield strength in the circumferential direction and across the wall thickness etc., significantly interfere in the definition of the demanding, in such projects, minimum wall thickness requirements.

Molecular dynamics simulation of multi-groove nano-milling

This article investigates the nano-milling of multi-grooves on single crystalline copper. To explore the material removal mechanisms, molecular dynamics (MD) simulations were carried on both sequential and simultaneous nano-milling processes. It was found that to obtain quality grooves; a simultaneous multi-grooving requires a larger wall thickness between two adjacent grooves. Under sequential nano-millings or a simultaneous nano-milling with same rotational direction of the tools, the minimum wall thickness can be identified by residual stress distribution analysis. Under a simultaneous nano-milling with opposite rotational direction of the tools, this requirement of minimum wall thickness is better identified by strain rate distribution analysis. Overall, the simultaneous nano-milling with opposite rotational direction of the tools gives the best groove quality. A detailed machinability analysis showed that the groove quality by nano-milling can be improved by increasing the depth of cut and wall thickness between two adjacent grooves.

Static and dynamic stress analysis of flat bottom-bamboo reinforced concrete silo for rough rice storage.

Concrete silos are one of the most robust and reliable structures for grain storage in tropical countries. This study analysed the structural behavior of a low cost, flat bottom bamboo-reinforced concrete (BRC) silo for rough rice storage. This research included the design and development of a BRC silo in accordance with the guidelines mentioned by the Indian Standard (IS) codes. The Finite Element Method was employed to develop the stress profile in the silo walls under “grain at rest” and “grain filling” conditions. The results obtained were further compared with experimental results, classic silo theories (Janssen’s theory) and standards of different countries in the world. The numerical technique gave stress magnitudes very close to those of the experimental results. The classic theories as well as the standards of different countries predicted an over estimation of the magnitude of stresses in the BRC silo. This would result in extra cost of construction of BRC silos. The study also suggested that the vertical stresses were most predominant under static and filling conditions. Maximum stresses were developed at the silo bottom. This study is expected to aid the development of economical silos with minimum wall thickness and material requirement which are ideal for on-site construction and use by smallholder farmers.

Analysis of the Stress Relieving Process in a Semiconductor Heterosystem with a (013) Interface

A theoretical analysis of the process of introducing misfit dislocations into a semiconductor heterostructure with a (013) interface is performed by assuming conditions of quasi-equilibrium process. The mechanism of generation is established for those misfit dislocations, which do not meet the requirement of minimum critical film thickness. The calculations are performed on the basis of the force balance model and allow for the shear stress field in the film and the type of the screw dislocation component.

Cyclic loading tests on exposed column-base plate weak-axis connections of small-size steel structures

Research on evaluating the seismic performance of exposed column-base plate weak-axis connections of small-size steel structures is substantially limited. Therefore, in this study, six exposed column-base plate weak-axis connection specimens with L-shaped anchor bolts under cyclic loading were tested. The primary test variables were the thickness of base plates, the presence of rib plates, and the number and embedment length of anchor bolts. Furthermore, round and threaded rods with L-shape were used as anchor bolts to assess the effect of bond performance. It was found that the structural performance of the connections was influenced by the thickness of base plate and the bond performance of anchor bolts. It should be noted that although base plate meets the minimum thickness requirements by the current design code, if the base plate yields before the moment capacity of steel column reaches the plastic moment, the structural performance of the connection will decrease. The connection details in this study can be considered semi-rigid connections. Threaded anchor bolts with L-shape are more preferred over the smooth round anchors for increased bond strength. Furthermore, equations for required tensile capacity and cross-sectional area for anchor bolts were derived in this study.

Comparison of technical and commercial aspects regarding cold forming, superplastic forming and hot deep drawing

AbstractTitanium parts can be very expensive or can be a good compromise between cost and efficiency especially when expected cost and weight reduction is reached or exceeded. Titanium properties are always well desired but the high level of material cost and the cost of manufacturing are not appreciated. Applicable forming processes for sheet metal parts range from conventional cold forming of commercially pure titanium with subsequent separate annealing up to hot forming processes like hot bending, hot calibration, hot deep drawing and superplastic forming with in‐process annealing. Each process has limitations and/or special advantages. There are big differences in material waste, cycle time, process cost, overweight from minimum wall thickness requirements and tool design. Suitable choice of process and the technical feasibility is mostly depending on part geometry also in respect of constant wall thickness and type of alloy. The paper describes decision guidelines to find the right process for a given inquiry concerning alloy, service loads, number of load cycles, temperature, quantity, optical appearance, etc. The total picture has to include the following assembly processes. Some representative solutions are described.

Reinforcement Placement in a Concrete Slab Object Using Structural Building Information Modeling

AbstractIn recent decades, the use of Reinforced Concrete (RC) structures such as conventional RC structures, flat plate structures, ribbed slabs, waffle slabs, etc. has become common in residential apartment buildings and mixed‐use buildings in the Far East, South East, Middle East, and around the world. Numerous experts work together for the design, construction, and supply of materials. Reinforcement bar configurations are usually designed and specified by structural engineers during the construction document phase without input from the project stakeholders such as rebar detailers, fabricators, and spacers. Rebar detailers use shop drawings to form reinforcement bars for fabrication and placement. The adoption of new technologies such as set‐based design and lean construction can save time and cost and ensure quality and safety during the construction process. This article examines and considers the contribution factors of downstream project stakeholders through their experiences such as rebar detailers, fabricators, and spacers during structural design using the Building Information Modeling (BIM) system. In this article, the novel modeling technology of placing reinforcement bar in the reinforced concrete flat plate floor system has been developed using the parametric design technology of 3D structural BIM, which can be converted into working drawings and shop drawings. The model can also be used for the rebar fabrication with an automatic bar bending and cutting machine. This research examines the interoperability among the structural model, the structural analysis and design results of a concrete flat plate that satisfy minimum thickness requirements and sustained and long‐term deflection criteria. The numerical experiment for the automated concrete flat plate modeling using a 66‐story mixed‐use building in a 3D virtual environment including reinforcement bar modeling using structural BIM has been completed as the part of this study.

Systems Engineering Methodology for Linking Requirements to Design Complexity and Manufacturing Trade Space Constraints

Aerospace system requirements over the last decade have continued to evolve toward higher levels of performance at lower cost, incurring a major challenge for system developers; how to balance conflicting performance and cost requirements and understand their impact on performance margins as well as the manufacturability characteristics of the design. This paper presents results of a case study performed on an aerospace air turbine starter system in which a top-level systems engineering methodology has been developed to help understand the impact that customer requirements and design decisions have on manufacturing trade space constraints. One of the major findings of this case study is that incremental increases in performance requirements can drive step change increases in manufacturing cost due to discontinuities in the material and process trade space, i.e. using titanium versus aluminum to meet temperature requirements or having to use investment versus sand castings to meet minimum thickness and tolerance requirements. Internally developed quantitative producibility analysis tools are also used to characterize the complexity and Design for Manufacturability (DFM) characteristics of the “similar to” baseline design to identify producibility improvement opportunities for the new design as part of the proposed systems engineering process to mitigate design reuse risks.

Thickness conditions for characterizing the periodic nanostructures with the retrieved electromagnetic parameters

By analyzing the convergence of the retrieved effective electromagnetic parameters, we presented that one wavelength of the propagating wave in the nanostructure is the minimum thickness requirement for effectively characterizing a finite thickness nanostructure. This thickness condition has been separately validated in a photonic crystal with negative refraction and in a typical fishnet metamaterial which has been investigated theoretically and experimentally before.

Minimum Thickness of Flat Plate Addressing Construction Load and Scheme

During construction of building structures, construction load significantly greater than the self-weight of a slab, is imposed on the early-age concrete slabs. As a result, according to the construction scheme, the construction load may causes excessive long term deflection and flexural cracking in a flat plate. However, the requirement of minimum thickness of the flat plate provided by the current design codes does not address such effect of the construction load on the slab. In the present study, a simplified design method was developed to calculate the deflection of a flat plate affected by the construction load and scheme. In the proposed method, a variety of design parameters affecting the long-term deflection of the plate was considered. Based on the proposed method, a design equation for estimating the minimum thickness of the flat plate was developed to be conveniently used in design work.

Thickness Optimization of SPF for Titanium Alloy Negative Angle Parts

With the Superplastic forming technology, the problem that the forming of the complex titanium alloy parts is difficult has been solved. The high temperature forming characteristics of the titanium alloy material and the establishment of the constitutive model of material that will be used as the material model of the simulation of the material forming (the minimum thickness is larger than 0.8 mm) about the negative Angle parts are based on high-temperature tensile test. The influence of the thickness of the parts is analyzed from three different SPF schemes, which are simulated by the MSC.MARC software. The results demonstrate the parts taking advantage of two-stage SPF, which is consisted of concave die SPF method and convex die SPF method can meet the requirement of minimum thickness and improve the thickness distribution on the die draft sides. Furthermore, the thickness distribution of the parts is more uniform with the convex die SPF method.

Critical Stress Intensity Factor Determination for AZ61 Magnesium Alloy

A stress intensity factor K was used as a fracture parameter to determine the plane strain fracture toughness KIC of AZ61 magnesium alloy using a single edge notch bend (SENB) specimen in accordance to ASTM E399 testing method. Five different specimen thicknesses of 2 to 10 mm were used in the test. A sharp fatigue pre-crack was initiated and propagated to half of specimen width at a constant crack propagation rate of about 1 x 10-8 m/cycle before the specimen was loaded in tension until the fracture stress is reached and then rapid fracture occurred. The fracture toughness KC values obtained for different thicknesses showed that KC value decreased with increasing specimen thickness. The highest KC value obtained was 16.5 MPa√m for 2 mm thickness specimen. The value of KC became relatively constant at about 13 MPa√m when the specimen thickness exceeds 8 mm. This value was then considered as the plane strain fracture toughness KIC of AZ61 magnesium alloy. Calculation of the minimum thickness requirement for plane strain condition and the size of the shear lips of the fracture surface validate the obtained KIC value.

The Impact of Probabilistic Modeling in Life-Cycle Management of Nuclear Piping Systems

Flow accelerated corrosion (FAC) is a serious form of degradation in primary heat transport piping system (PHTS) of the nuclear reactor. Pipes transporting hot coolant from the reactor to steam generators are particularly vulnerable to FAC degradation, such as tight radius pipe bends with high flow velocity. FAC is a life limiting factor, as excessive degradation can result in the loss of structural integrity of the pipe. To prevent this, engineering codes and regulations have specified minimum wall thickness requirements to ensure fitness for service of the piping system. Nuclear utilities have implemented periodic wall thickness inspection programs and carried out replacement of pipes prior to reaching an unsafe state. To optimize the life-cycle management of PHTS, accurate prediction of time of replacement or “end of life” of pipe sections is important. Since FAC is a time-dependent process of uncertain nature, this paper presents two probabilistic models for predicting the end of life. This paper illustrates that the modeling assumptions have a significant impact on the predicted number of replacements and life-cycle management of the nuclear piping system. A practical case study is presented using wall thickness inspection data collected from Canadian nuclear plants.