Computers—the key to reliable ceramic materials and components

Abvanced structural ceramic components are increasingly used in demanding engineering applications. A major impediment to even wider utilization are issues related to reliability and affordability. Exercising greater control over the inherent flaw population in the ceramic component will contribute importantly to resolving these two issues. Computers will play an ever-increasing role in designing to minimize the impact of flaws, in processing to minimize the presence of flaws, and in nondestructive testing (NDT) to assure the absence of critical flaws for reliable, affordable ceramic components. This article reviews the state of the art and/or the potential for the application of computers in the design, fabrication, and inspection of structural ceramic components. A strategy for the integration of design, processing and NDT will be presented.     

落锤试验试样厚度尺寸效应对T_(NDT)的影响

以3种供应状态、5种钢材、6型试样的落锤试验数据说明钢材的无塑性转变温度TNDT不仅与材料有关,而且与试样厚度有关,二者的关系可用函数式TNDT=At-m+B表示,式中的A、B、m是与材料有关的参数。为准确客观地反映实际工程材料的断裂特性,保证断裂设计的安全可靠,推荐采用厚度为12～50mm的6型落锤试样(P1～P6)和相应的试验条件。     

Solving some key failure analysis problems using advanced methods for materials testing

A dilemma encountered in engineering practice is a proliferation of newly designed (mostly high-strength and/or corrosion-resistant) steels and alloys that are unusable in industry as they are highly susceptible to failure under operating conditions including environmentally assisted cracking. The problem of materials failure has several sources, the most significant of which is how engineers select which material to use in which industry. As a rule, selection is based solely on assessing the mechanical properties of materials with little or no consideration of how these mechanical properties will interface with specific operating parameters found within different industries. The functional design, selection and use of materials aimed at preventing in-service failures depends, therefore, on finding testing methods, standards and approaches appropriate to real operating conditions guided by analysis of material performance under those conditions.     

Engineering long term clinical success of advanced ceramic prostheses

Biocompatability and, in some applications, esthetics make all-ceramic prostheses compelling choices but despite significant improvements in materials properties and toughening mechanisms, these still have significant failure rates. Factors that contribute to the degradation in strength and survival include material selection and prosthesis design which set the upper limit for performance. However, fabrication operations introduce damage that can be exacerbated by environmental conditions and clinical function. Using all-ceramic dental crowns as an example, experimentally derived models provide insight into the relationships between materials properties and initial critical loads to failure. Analysis of fabrication operations suggests strategies to minimize damage. Environmental conditions can create viscoplastic flow of supporting components which can contribute additional stress within the prosthesis. Fatigue is a particularly challenging problem, not only providing the energy to propagate existing damage but, when combined with the wet environment, can create new damage modes. While much is known, the influence of these new damage modes has not been completely elucidated. The role of complex prosthesis geometry and its interaction with other factors on damage initiation and propagation has yet to be well characterized.     

Failure prevention in bonded joints on primary load bearing structures

Adhesive bonding is a particularly effective method of assembling complex structures, especially those made from different materials. Provided the joint is well designed, the adhesive bond ought to be one of the strongest aspects of the structure and most certainly should not be the life limiting factor. This of course pre-supposes that the joint has been correctly executed. The major factors determining the integrity of an adhesive bond are selection of the most appropriate adhesive, joint design, preparation of the bonding surfaces, strict quality control in production and condition monitoring in service. Adhesives have become increasingly important in assembling many of the multi-material structures which make up a contemporary Formula 1 racing car. Structural fibre reinforced composite materials were introduced into Formula 1 motor racing in 1980. Since then the cars have become increasingly dependent on these materials such that the weight of a state-of-the-art chassis may consist of up to 80% of carbon fire reinforced epoxy resins and the appropriate adhesives to facilitate fabrication. One might argue, therefore, that a modern Formula 1 chassis consists of a series of “plastic” mouldings held together with glue! Many of these structures are very highly stressed and required to operate in aggressive environments, particularly high temperatures. The consequences of failure of “Class A” structures can be catastrophic to the operation of the vehicle and impinge on the safety of the driver. Although increasingly better understood, the science and engineering of adhesives is very much in its infancy. Consequently, the design and operation of bonded components tends to be a constantly evolving, semi-quantitative process that combines fracture and finite element analysis with practical experience. In recent years BAR Honda have been very successful using and developing adhesive technology. The process of “total quality management” (TQM) encompasses the whole operation from R&D and design through materials procurement, component manufacture and condition monitoring to ensure successful exploitation up to the point of withdrawal from service.     

Bioinspired engineering of honeycomb structure – Using nature to inspire human innovation

Honeycomb structures, inspired from bee honeycombs, had found widespread applications in various fields, including architecture, transportation, mechanical engineering, chemical engineering, nanofabrication and, recently, biomedicine. A major challenge in this field is to understand the unique properties of honeycomb structures, which depended on their structures, scales and the materials used. In this article, we presented a state-of-the-art review of the interdisciplinary efforts to better understand the design principles for products with honeycomb structures, including their fabrication, performance (e.g., mechanical, thermal and acoustic properties) as well as optimization design. We described how these structural perspectives have led to new insights into the design of honeycomb structures ranging from macro-, micro- to nano-scales. We presented current scientific advances in micro- and nano-technologies that hold great promise for bioinspired honeycomb structures. We also discussed the emerging applications of honeycomb structures in biomedicine such as tissue engineering and regenerative medicine. Understanding the design principles underlying the creation of honeycomb structures as well as the related scientific discovery and technology development is critical for engineering bioinspired materials and devices designed based on honeycomb structures for a wide range of practical applications.     

Sicherer und wirtschaftlicher Betrieb von Kraftwerken – Ergebnis der Forschung im Bereich Werkstoffe,Auslegung und Instandhaltung

Safe and Economic Operation of Power Plants – Research Results in the Field of Materials, Design and Maintenance Components of power plants which undergo high temperatures are subjected to complex loading situations. The requirements on the used materials result from the special operation conditions of the plants and have to be adjusted to the steadily growing requirements on higher efficiency of the complete power plant as well as to those of safe and economic operation. The expenses for control and downtimes are directly connected with economic efficiency and availability. However, in case of new procedures or components it is not possible to revert to the existing know‐how. Different failure mechanisms than known before can occur. The same goes for the load situation. Therefore the knowledge base has to be extended to in‐advance or even parallely running scientific examinations that life assessment and maintenance strategies can be applied which guarantee the operational reliability and the efficiency of the plant. The main emphasis of these F&E works has to be put on condition monitoring based on actual operational data, the standard materials’ and component’s behaviour (deformation, damage and failure behaviour) in connection with design of components and the related material laws. In the framework of applied AVIF projects, following problems are handled:. – qualification of materials by determinating parameters related to practise. – optimal design of components by making available material laws and numerical tools. – economic manufacturing of components by qualifying processing methods such as welding. – The results can be transferred to concepts for safe and economic operation of power plants, especially for newly introduced materials for which there is no operational experience available.     

Metallurgical failure analysis of cold cracking in a structural steel weldment: Revisiting a classic failure mechanism

Cold cracking of structural steel weldments is a well-characterized, well-documented, and well-understood failure mechanism. Extensive effort has been put forth to recognize the welding and materials selection parameters that are conducive to cold cracking; however, these engineering efforts have not fully eliminated the occurrence of such failures. This article describes cold cracking failure specifically related to the construction industry. This particular failure was successfully identified prior to final erection of the structural member, and the weld was successfully reworked. These actions potentially prevented a serious catastrophic event that could have occurred have occurred either later in the construction process or possibly during the use of the building. Individual welding parameters, such as electrode/wire selection, joint design, and pre/postheating, played a role in the failure, and a number of human factors relating to the actual fabrication practices also contributed to the failure process.     

Improved productivity through failure analysis: Case studies in precision forging of aerospace components

In this study, usefulness of failure analysis in improving productivity through selection of better materials and heat treatments that delay or prevent the on set of fracture in precision forging of aerospace components is illustrated. Examples have been taken from failed cold working dies, hot forging dies and broaches. Detailed metallographic analysis of the microstructures and fractures has pinpointed the sources and mechanisms of failure. This, in turn, has indicated the means of preventing such failures in service and, in improving die life and performance, by using advanced materials and optimizing heat treatments and surface engineering treatments.     

反应器冷却水管失效分析与改进措施

应用化学分析、金相和电子探针显微分析技术对反应器中冷却水管的失效原因进行了分析.结果表明,冷却水管发生早期失效是由于构件发生应力腐蚀开裂所致.基于材料使用环境考虑,在选材和结构设计两个方面采取了改进措施,延长了冷却水管的使用寿命.     

SIL analysis of subsea control system components based on a typical OREDA database

Proper performance evaluation of subsea system components is of high significance for reliable operation and remote monitoring or the replacement of the components before the occurrence of any failure. As a part of subsea systems, subsea control system (SCS) plays a key role in accomplishing a reliable performance. Hence, achieving knowledge of the components’ failure rates is highly important in the safety analysis of SCS. To the author's knowledge, limited work is done on the safety analysis of SCS using failure rates for a multitude of components. Also, the number of research papers that are based on industrial works is restricted. Hence, this paper aims to provide a noticeable contribution in fulfilling the referred gap. For this purpose, a safety integrity-level (SIL) analysis is proposed based on a typical OREDA database. In the implementation of the proposed SIL, a failure mode classification table is provided for a selection of SCS components. This is followed by the estimation of several parameters, such as the total time in service, as well as obtaining the values of critical failure rates. The analysis indicates that signal failure is the failure mode occurring more than the other ones. Also, the subsea electronic module yields the highest value of critical failure rates. Besides, a comparison of parameter values is provided for two different versions of the utilized database.     

Failures of engineering components due to environmentally assisted cracking

Examples of failures of engineering components by stress-corrosion cracking, corrosion-fatigue, hydrogen embrittlement, liquid-metal embrittlement, and solid-metal embrittlement are described. Causes of failure include inappropriate materials selection or heat treatment, poor design, and high residual stresses. The examples illustrate how fractographic characteristics, analysis of films and deposits on fracture surfaces, and other factors help in diagnosing the modes and causes of failures, thereby enabling the appropriate remedial measures to be taken.     

A Microstructural and Fractographic Study on the Failure of a Drive Shaft

The automotive industry is one of the most dynamic and competitive segments of the international economy and it has invested considerable resources into the research and development of new components and the improvement of existent pieces. Nonetheless, failures continue to occur, often because of defects in a component. Failure analysis uses several techniques to investigate causes of the defect which led to the failure of a component, equipment, or structure. Usually, these causes are related to the use of inadequate materials, the presence of defects which appear during fabrication or design errors, or improper assembly, maintenance and use. Knowledge about these causes and the correction of such anomalies allow the improvement of the performance of components regarding both efficiency and safety. In this study, the results of the failure analysis of the drive bar of a police car are presented and light optical microscopy and scanning electron microscopy (SEM) results are used to show that the presence of an already existent defect and an unfavorable microstructure led to the occurrence of brittle fracture which caused the premature and catastrophic failure of this component.     

Stress-Based Uniaxial Fatigue Analysis Using Methods Described in FKM-Guideline

The process of prevention of failure from structural fatigue is a process that should take place during the early development and design phases of a structure. In the ground vehicle industry, for example, the durability specifications of a new product are directly interweaved with the desired performance characteristics, materials selection, manufacturing methods, and safety characteristics of the vehicle. In the field of fatigue and durability analysis of materials, three main techniques have emerged: nominal stress-based analysis, local strain-based analysis, and fracture mechanics analysis. Each of these methods has their own strengths and domain of applicability??for example, if an initial crack or flaw size is known to exist in a structure, a fracture mechanics approach can give a meaningful estimate of the number of cycles it takes to propagate the initial flaw to failure. The development of the local strain-based fatigue analysis approach has been used to great success in the automotive industry, particularly for the analysis of measured strain time histories gathered during proving ground testing or customer usage. However, the strain life approach is dependent on specific material properties data and the ability to measure (or calculate) a local strain history. Historically, the stress-based fatigue analysis approach was developed first??and is sometimes considered an ??old?? approach??but the stress-based fatigue analysis methods have been continued to be developed. The major strengths of this approach include the ability to give both quantitative and qualitative estimates of fatigue life with minimal estimates on stress levels and material properties, thus making the stress-based approach very relevant in the early design phase of structures where uncertainties regarding material selection, manufacturing processes, and final design specifications may cause numerous design iterations. This article explains the FKM-Guideline approach to stress-based uniaxial fatigue analysis. The Forschungskuratorium Maschinenbau (FKM) was developed in 1994 in Germany and has since continued to be updated. The guideline was developed for the use of the mechanical engineering community involved in the design of machine components, welded joints, and related areas. It is our desire to make the failure prevention and design community aware of these guidelines through a thorough explanation of the method and the application of the method to detailed examples.     

Mechanical damping behavior of Al/C60-fullerene composites with supersaturated Al–C phases

Al-based materials with enhanced mechanical damping properties are of great interest in aerospace and automotive industries as engineering materials for critical components that suffer from severe dynamic environment. In this report, we developed Al/C₆₀-fullerene composites to increase damping capacity by the supersaturated Al–C phases. Carbon atoms, dissolved from individually dispersed C₆₀-fullerenes, are intercalated into the Al interstitial sites, producing Al–C phases with expanded lattice structures. These novel nanostructures exhibit a superior mechanical damping behavior compared to monolithic Al, throughout the temperature range of room temperature to 350 °C. The present approach to control the lattice structure thus represents a new engineering paradigm for atomic-level design of lightweight structural components.     

耐火材料发展概述

本文简要介绍了中国耐火材料现状, 结合高温工业技术发展需求, 阐述了耐火材料的发展态势和发展方向。指出结构功能一体化设计与制备是以长寿化、功能化、轻量化、智能化、绿色化为特征的先进耐火材料发展的核心。结合新型高效隔热耐火材料、钢铁冶金连铸用先进功能耐火材料的研究, 介绍了先进耐火材料的组成-结构-性能-功能一体化设计理念与制备技术, 采用有限元数值模拟、融合先进陶瓷技术及梯度多层复合设计, 实现了关键服役性能的最优化设计与制备。     

Interaction of design,manufacturing method,and material selection

Abstract

The characterisation of a design in terms of function, appearance, manufacturing method, and cost is considered. The interacting influences of design, fabrication, and materials selection are not always appreciated, which results in inefficiency or failure. This is considered in an historical setting, highlighting the changes in circumstance which now require better communication of information for such interaction to occur. The role of the computer in the provision of databases from standardised information and the development of ‘intelligent’ selector systems with input to models from consideration of microstructural engineering is outlined. The greatly increased range of materials to be considered and the need for integration of design, processing, and materials expertise, poses problems for the teaching of materials engineering where, again, the computer has an important role to play in developing understanding. In this very important area of industrial and educational endeavour, interaction should progress towards integration.

MST/1063     

Rational Design of Carbon‐Rich Materials for Energy Storage and Conversion

Carbon‐rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom‐up constructed carbon‐rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon‐rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure–property relationships of the resultant carbon‐rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon‐rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon‐rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.     

基于Ansys的重型包装钢架箱工程轻量化设计

目的以某重型装备的运输用框架结构为研究对象,提出工程轻量化的设计准则及设计方案,以解决重型装备过度包装的问题。方法利用Ansys软件对运输用钢架包装箱的起吊工况和堆码工况进行数值仿真分析,并基于分析结果对经验设计方案进行改进。结果优化后的钢架箱质量减少了942kg,质量减少比例达到了43%,起吊工况静强度安全系数为2.14,堆码工况静强度安全系数为1.94,稳定性安全系数有4.96倍。结论工程轻量化设计后的钢架箱满足屈服强度失效准则和稳定性失效准则规定的安全性能,提高了材料的使用效率,包装成本显著减少。     

Blind multiridge detection for automatic nondestructive testing using ultrasonic signals

Ultrasonic imaging has been a significant means for nondestructive testing (NDT). Recently the NDT techniques via the ultrasonic instrumentation have shown the striking capability of the quality control for the material fabrication industry. To the best of our knowledge, all existing signal processing methods require either the a priori information of the ultrasonic signature signals or the manual segmentation operation to achieve the reliable parameters that characterize the corresponding mechanical properties. In this paper, we first provide a general mathematical model for the ultrasonic signals collected by the pulse-echo sensors, then design a totally blind novel signal processing NDT technique relying on neither a priori signal information nor any manual effort. Based on the automatic selection of optimal frame sizes using a proposed new criterion in our scheme, the signature signal can be blindly extracted for further robust multiridge detection. The detected ridge information can be used to estimate the transmission and attenuation coefficients associated with any arbitrary material sample for the fabrication quality control.