Search Results for post-impact fatigue

This article presents the damage tolerance criteria for military composite aircraft structures to safely operate the structures with initial defects or in-service damage. It describes the effects of defects, such as wrinkles in aircraft structures, and the reduction in compressive strength and tensile strength. The article reviews low velocity impacts in aircraft structures in terms of resin toughness, laminate thickness, specimen size and impactor mass, and post-impact fatigue. It explains the tension strength analysis, such as linear elastic fracture mechanics and R-curve methods, to predict the residual strength of the structures.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of AISI/SAE alloy steels (4xxx steels) and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the brittle fracture, ductile fracture, impact fracture, fatigue fracture surface, reversed torsional fatigue fracture, transgranular cleavage fracture, rotating bending fatigue, tension-overload fracture, torsion-overload fracture, slip band crack, crack growth and crack initiation, crack nucleation, microstructure, hydrogen embrittlement, sulfide stress-corrosion failure, stress-corrosion cracking, and hitch post shaft failure of these steels. The components considered in the article include tail-rotor drive-pinion shafts, pinion gears, outboard-motor crankshafts, bull gears, diesel engine bearing cap bolts, splined shafts, aircraft horizontal tail-actuator shafts, bucket elevators, aircraft propellers, helicopter bolts, air flasks, tie rod ball studs, and spiral gears.

Structure-property relationships for metal additive manufacturing (AM) using solidification-based AM processes (e.g., powder-bed fusion and directed-energy deposition) are the focus of this article. Static strength and ductility properties in AM materials are impacted heavily by the microstructure but are also affected by porosity and surface roughness. Fatigue failure in AM materials is also influenced by porosity, surface roughness, microstructure, and residual stress due to applied manufacturing processing parameters. Post-processing treatments can further influence fatigue failure in AM materials.

This article illustrates typical fractographic features for a number of different composite materials. It describes the differences in fracture characteristics due to different loading, material processing, and environmental conditions. The article presents fractographic data obtained from epoxy matrix materials. Minimal fractographic data from other brittle thermoset resin systems are also presented. The article discusses the interlaminar fracture of composites with ductile thermoplastic matrices. It also provides information on the translaminar fracture features of the composite materials.

This datasheet provides information on key alloy metallurgy, processing effects on physical and mechanical properties, and applications of natural aging casting alloys 711.0 and 712.0. The fatigue strength of smooth and notched permanent mold aluminum casting of C712.0-F is illustrated.

Knowledge of fatigue behavior at the laminate level is essential for understanding the fatigue life of a laminated composite structure. This article describes fatigue failure of composite laminates in terms of layer cracking, delamination, and fiber break and interface debonding. It discusses the fatigue behavior of composite laminates in the form of a relation between applied maximum fatigue stress and fatigue life. The article explains Weibull distribution and parameters estimation for fatigue data analysis and life prediction of composite laminates. It analyzes the fatigue properties and damage tolerance of fiber-metal laminates such as ARALL and GLARE laminates. The article concludes with a discussion on the effects of fatigue on notched and unnotched specimens.

This article illustrates typical wear and friction issues encountered in gas and steam turbines and their consequences as well as commonly adopted materials solutions. It contains tables that present the summary of wear and friction related issues encountered in steam turbines and gas turbines. The article outlines the differences in the operating conditions and the nature of the components involved in gas and steam turbines. It discusses the constraints and applicable coating solutions for wear and friction issues, and concludes with a broad set of challenges that need to be addressed to improve performance and operability of gas and steam turbines.

Hot isostatic pressing (HIP) is used to eliminate porosity in castings. This article provides a history and an overview of the HIP system. It illustrates the reasons for using HIP and discusses the criteria for selecting HIP process parameters. The main mechanisms by which pores are eliminated during HIP are reviewed. The article describes the effect of HIP on the mechanical properties, shape, and structure of castings as well as the effect of inclusions on as-HIPed properties. It examines the problems encountered in HIP and their solution. The article concludes with information on the economics of HIP processing.

Fatigue failure is a critical performance metric for additively manufactured (AM) metal parts, especially those intended for safety-critical structural applications (i.e., applications where part failure causes system failure and injury to users). This article discusses some of the common defects that occur in laser powder bed fusion (L-PBF) components, mitigation strategies, and their impact on fatigue failure. It summarizes the fatigue properties of three commonly studied structural alloys, namely aluminum alloy, titanium alloy, and nickel-base superalloy.

This article provides a general overview of additively manufactured steels and focuses on specific challenges and opportunities associated with additive manufacturing (AM) stainless steels. It briefly reviews the classification of the different types of steels, the most common AM processes used for steel, and available powder feedstock characteristics. The article emphasizes the characteristics of the as-built microstructure, including porosity, inclusions, and residual stresses. It also reviews the material properties of AM steel parts, including hardness, tensile strength, and fatigue strength, as well as environmental properties with respect to corrosion resistance, highlighting the importance of postbuild thermal processing.

This article presents the failure of polymer-matrix composites and the methodology for fractography. It provides a detailed discussion on the types of translaminar, interlaminar, and intralaminar failures. The article also presents a discussion on the types of fatigue failures, and the influence of composite architecture. It provides details of the fractography associated with defects and damage.

This article presents the structural attributes and internal characteristics of spot welds as well as the commonly inspected imperfections in resistance welds. It describes the industrial requirements for weld quality. Commonly performed destructive evaluations, namely, manual testing, quasi-static mechanical tests, dynamic mechanical tests, and metallographic examination, are reviewed. The article reviews weld-quality monitoring using various process signals and provides a discussion on the on-line and off-line nondestructive evaluation methods of spot weld quality.

This article discusses corrosion fatigue, its effects on the damage tolerance of aircraft, and its predictive modeling. A conceptual framework is presented that incorporates two distinctive cyclic-based life-prediction philosophies and expands them both to include the time domain in order to consider the effects of corrosion. These philosophies include crack initiation used for safe-life design and crack growth used for damage tolerance. The article presents the methodology for computing the effects of real-time age degradation on an aircraft structure for two different corrosion types: crevice and pitting corrosion. It describes the rationale and techniques needed to apply the age-based structural integrity processes to in-service structures in order to realize the benefits throughout the full structural life cycle.

This article describes the role of the full-scale testing in assessing composite structural systems of aircraft and qualifying them for in-service use. The typical full-scale tests include static, durability, and damage tolerance. The article discusses the parameters to be considered when developing the basic requirements for the static test. These parameters consist of material considerations, moisture and temperature effects, structure size, load application alternatives, instrumentation requirements, test procedure considerations, ultimate load requirements, and test results correlation. The basic requirements common for durability and damage tolerance tests, including environmental effects and inspection requirements, are also discussed.

This article reviews the emerging manufacturing technology that is alternatively called additive manufacturing (AM), direct digital manufacturing, free-form fabrication, three-dimensional (3-D) printing, and so on. It provides a broad contextual overview of metallic AM. The article focuses on the mechanical properties of AM-processed Ti-6Al-4V, IN-625, and IN-718. The development of closed-loop, real-time, sensing, and control systems is essential to the qualification and advancement of AM. This involves the development of coupled process-microstructural models, sensor technology, and control methods and algorithms. AM has the potential to revolutionize the global parts manufacturing and logistics landscape. It enables distributed manufacturing and the productions of parts on demand while offering the potential to reduce cost, energy consumption, and carbon footprint. The article explores the materials science, processes, and business considerations associated with achieving these performance gains. It concludes that a paradigm shift is required to fully exploit AM potential.

This article begins with a review of the purposes of mechanical characterization tests and the general considerations related to the mechanical properties of anisotropic systems, specimen fabrication, equipment and fixturing, environmental conditioning, and analysis of test results. It provides information on the specimen preparation, instrumentation, and procedures for various mechanical test methods of fiber-reinforced composites. These include the compression test, flexure test, shear test, open hole tension test, and compression after impact test. The article describes three distinct fracture modes, namely, crack opening mode, shearing mode, and tearing mode. It presents an overview of fatigue testing and fatigue damage mechanisms of composite materials and reviews the types of mechanical measurements that can be made during the course of testing to assess fatigue damage. The article concludes with a discussion on the split-Hopkinson pressure bar test.

Bearing in mind the three-legged stool approach of device design/manufacturing, patient factors, and surgical technique, this article aims to inform the failure analyst of the metallurgical and materials engineering aspects of a medical device failure investigation. It focuses on the device "failures" that include fracture, wear, and corrosion. The article first discusses failure modes of long-term orthopedic and cardiovascular implants. The article then focuses on short-term implants, typically bone screws and plates. Lastly, failure modes of surgical tools are discussed. The conclusion of this article presents several case studies illustrating the various failure modes discussed throughout.

This article describes methods for analyzing impact-damaged composites in the aircraft industry. These include C-scan and x-radiography methods and optical microscopy. The article reviews brittle-matrix composite and tough-matrix composite failures. It explains the different types of composite failure mechanisms such as thermoplastic-matrix composite failure mechanisms, untoughened thermoset-matrix composite failure mechanisms, toughened thermoset-matrix composite failure mechanisms, dispersed-phase and rubber-toughened thermoset-matrix composite failure mechanisms, and particle interlayer-toughened composite failure mechanisms.

This article focuses on common failures of the components associated with the flow path of industrial gas turbines. Examples of steam turbine blade failures are also discussed, because these components share some similarities with gas turbine blading. Some of the analytical methods used in the laboratory portion of the failure investigation are mentioned in the failure examples. The topics covered are creep, localized overheating, thermal-mechanical fatigue, high-cycle fatigue, fretting wear, erosive wear, high-temperature oxidation, hot corrosion, liquid metal embrittlement, and manufacturing and repair deficiencies.

Powder forging is a process in which unsintered, presintered, and sintered powder metallurgy preforms are hot formed in confined dies. This article provides information on the basic forms of powder forging and describes the material considerations, process considerations, and mechanical properties of powder forged (PF) steels. It reviews the parameters involved in quality assurance tests for PF parts. The article includes examples of PF components and highlights the reasons for selecting them over those made by competing forming methods.