Recent advances in the development of aerospace materials

A critical review of recent advances in the aerospace materials

The Ni–base alloys used as construction material in light water reactors (LWRs) have experienced stress corrosion cracking (SCC). Although SCC of wrought Ni–base Alloy 600 has been observed in operating plants for many years, until recently, the weld metal Alloys 82 and 182 used with Alloy 600 environmentally assisted cracking has not been widely observed in the field. However, laboratory tests indicate that in PWR coolant environments, the SCC susceptibility of Alloy 182 may be greater than that of Alloy 600, and that of Alloy 82 may be comparable to Alloy 600. This paper presents crack growth rate (CGR) results for Alloys 182 and 82 from the reactor vessel nozzle-to-pipe from the V. C. Summer plant under both constant and cyclic load. The tests were conducted on 1/2-T compact tension specimens in a simulated PWR environment at 320 °C. Crack extensions were measured by DC potential drop measurements. Characterization of the material microstructure and is described. The SCC growth rates are compared with the existing CGR data for Ni–alloy welds to evaluate the effects of alloy type, weld microstructure, and stress intensity factor K on CGRs. The cyclic CGRs for these alloys are compared with CGRs that are expected for Alloy 600 in air under the same mechanical loading conditions to obtain a qualitative understanding of the degree and range of conditions for significant environmental enhancement in growth rates. A detailed characterization of the fracture morphology is also presented.

Corrosion and stress corrosion cracking in supercritical water

Stress corrosion cracking (SCC) of steels and Ni-base alloys in the pressurized water reactor (PWR) primary circuit has been a cause for reactor outages for many decades. Although the nuclear industry has made a considerable research effort to understand and predict SCC in this system, this enterprise is complicated by the sheer number of interdependent variables that have a major influence on the degradation behavior. SCC is highly time-dependant and often only sets in after many years. Therefore, autoclave testing, even with accelerating conditions, is an expensive and time-consuming endeavor. However, the results collected by a great number of research groups over many years have identified the most important parameters and, in many cases, how they influence the degradation behavior. The community has been constantly working on the development of a general theory that encompasses the underlying mechanisms and is capable of describing and predicting the observed degradation behavior. In the last two decades, the focus of research has shifted from the traditional approach of autoclave testing (for susceptibility and crack growth rates) to high-resolution microscopy and chemical analysis. The newly available techniques are providing data on chemical and structural changes locally at the crack tip where SCC occurs. The techniques covered in this review can provide very high chemical sensitivity at atomic resolution, which is ultimately needed in the quest for a generalized theory.

Stress corrosion cracking (SCC) tests were conducted under the supercritical-water cooled power reactor (SCPR) coolant conditions, which are predicted to consist of wide temperature range, extremely high pressure, and high dosage of neutron irradiation. This paper describes the results of SCC tests for austenitic stainless steels and a Ni base alloy. The susceptibility to intergranular stress corrosion cracking (IGSCC) was evaluated by slow strain rate tests (SSRTs), which were performed using a supercritical-water (SCW) test loop. The results for sensitized Type 304 SS indicated that the SCC susceptibility decreased with increasing temperature. The upper limit temperature of SCC susceptibility for sensitized type 304 SS existed at around 400°C, above which IGSCC did not occur in oxygenated supercritical water. No IGSCC of Type 316L SS and Alloy 600 was exhibited in fracture surface under SCPR conditions, even though small cracks were observed in side surface.

LIMITED DEVELOPMENT OF INNOVATIVE INSTRUCTIONAL MATERIALS Paralleling the limited concept of teaching objectives in general, the development of innovative instructional materials has been equally limited. A body of research related to cognitive processes and learning has been developing, but the theoretical ideas that have stimulated this research have not been tested in the development of teaching materials. Although the development of new materials has grown as a response to some of the main problems of education today, research on the cognitive processes has been little considered for the contribution it can make toward the writing of effective materials. Innovative materials have been written for many fields of study including mathematics, physics, chemistry, biology, English, and some areas of social studies, but they are developed on the basis of dissatisfaction with present materials. A general theory for generating the materials does not exist.

The reduction of cycling capacity degradation of Mg–Ni-based electrode alloys by Fe substitution

Performance assessment and design of ultra-high performance concrete (UHPC) structures incorporating life-cycle cost and environmental impacts

Smart materials are at the cutting edge of modern engineering. Their ability to respond dynamically to changes in the environment enables adaptive and efficient systems. The need in the aerospace industry for lighter, energy-efficient, and highly adaptive materials has driven further development and integration of smart materials into aircraft, spacecraft, and satellite structures. These materials have been applied to the development of morphing wings, vibration control systems, deployable components, and structural health monitoring and have greatly contributed to flight efficiency and reliability. However, they are not widely applied because of limitations, such as temperature sensitivity, fatigue resistance, low actuation force, and scalability issues in large-scale aerospace applications. The solution to these challenges is crucial for ensuring the long-term durability and safety of smart materials under extreme conditions in the aerospace industry. This study focuses on the development, mechanism application, and future development of the following three popular smart materials: Shape Memory Alloys, Piezoelectric Materials, and Electroactive Polymers. The strength of each material will be discussed together with its limitations and how it is being used in the transformation of engineering within the aerospace sector. It highlights how smart materials have increasingly become active players in providing adaptive, sustainable, and high-performance aerospace systems, and critically reviews challenges from smart materials that are faced by real-world aerospace applications, with their potential solution and long-term viability.

The aerospace engineering field is witnessing an evolution towards lightweight materials driven by the unwavering pursuit of improved performance and efficiency. Lightweight materials play a critical role in aerospace structures, and this thorough examination explores their significant influence on mission success, design, and fuel efficiency. Key developments in several material categories such as composites, metals, and polymers are methodically examined in this study, revealing their special qualities and potential uses. The historical viewpoint lays out a chronology of the development of materials, charting significant turning points that have influenced the use of lightweight materials in aerospace. The following sections delve into each lightweight material in great detail, explaining composites, alloys (including titanium, aluminium, and high-strength steel), and sophisticated polymers, along with their features, production methods, and uses. An examination of particular varieties and production nuances in the context of aerospace composite materials highlights their benefits in achieving unmatched strength-to-weight ratios. By elucidating their qualities and expanding uses in aircraft constructions, advanced metallic alloy research reveals the most recent advancements in materials like titanium and aluminium. A thorough examination of polymeric materials and nanocomposites reveals their critical role in the creation of lightweight structures. Their distinctive qualities and new uses are emphasized, highlighting their role in the ongoing revolution in aeronautical design. With a comprehensive examination of additive manufacturing and sophisticated machining methods essential to the realization of lightweight aircraft structures, innovative manufacturing technologies take center stage. Additionally, the assessment thoroughly evaluates the longevity and structural integrity of lightweight materials, addressing issues related to corrosion, fatigue, and other crucial elements. Investigations from actual applications provide concrete instances of lightweight materials being successfully used in aerospace projects, shedding light on the materials' performance and tangible advantages in various situations. Looking ahead, the paper's conclusion forecasts forthcoming developments in lightweight materials and clarifies possible obstacles and future research avenues that may influence the course of aerospace engineering. To underscore the critical role that lightweight materials play in aeronautical constructions, this paper synthesizes a variety of knowledge. It highlights the revolutionary potential of lightweight materials in influencing the future of aeronautical engineering, not only synthesizing current knowledge but also laying out a path for further study and innovation.

Failure probability analyses for PWSCC in Ni-based alloy welds

Insights into stress corrosion cracking mechanisms from high-resolution measurements of crack-tip structures and compositions

Crack growth test data of Ni-base alloys under cyclic loading in simulated boiling water reactor (BWR) environment including the effects of load rising time (tr) were evaluated in the view points of both fatigue and stress corrosion cracking (SCC). When the test data were plotted in the relationship between da/dt and Kmax, da/dt monotonically decreased with increasing tr and the stress ratio (R). For alloy 182 weld metal under short tr and/or low R, the crack growth rate assuming SCC is much lower than those of the test data. For alloy 182 under tr = 30 and 1000 s at R = 0.8, the crack growth rate assuming SCC almost coincided with test data. For heat affected zone (HAZ) of alloy 600 base metal (600HAZ), the crack growth rate assuming SCC had much different slope of da/dN-ΔK relationship compared with the test data in the tested range of tr up to 3000 s. From these observations, the contribution of SCC is relatively small and the main mechanism of crack growth is thought to be fatigue for the tested range (tr=1 to 1000 s for weld metal, tr=1 to 3000 s for base metal and R = 0.1 to 0.8). It was assured that the fatigue crack growth formula proposed by the authors accounts the effect of SCC adequately at long tr. Additionally, the applicability of the fatigue crack growth rate formula for austenitic stainless steels to the long term cyclic load was investigated and it was found that the formula can be applied to tr=30000 s.

This summary report presents a condensation of the designs as developed from requirements and concept selection to preliminary design. The study consists of the following six tasks: (1) Design requirements: establish design environmental conditions and criteria. Develop methodology to both assess SKSS reliability and performance, and minimize life cycle costs. (2) Conceptual design: develop at least two SKSS conceptual designs for both barge and spar platform (eight in all). Consider commercial plant SKSS, verify feasibility, define problem areas, estimate life cycle cost. Develop deployment, operation and maintenance scenarios. Recommend an SKSS concept for each platform. (3) Preliminary design; prepare preliminary designs for two SKSS concepts selected by NOAA/DOE. Optimize the designs, provide deployment and retrieval procedures, support requirements, evaute reliability and performance. Assess effects of watch circle and water depth variation. (4) Development and testing recommendations: recommend programs required to confirm design assumptions and performance predictions, including material and component development, and soils investigation. Estimate cost and schedule required to perform these programs. (5) Cost-time analysis: develop a detailed cost and schedule for the acquisition, transportation, deployment, inspection, maintenance, spares, replacement and salvage for the SKSS designs. (6) Commercial plant SKSS recommendations: assess applicability of designs to commercial plant SKSS. Recommend development program and at-sea tests as requied with estimate of cost and schedule. (WHK)

The demand of today’s and future spacecrafts for a stable platform for critical payloads is the driving force behind the coefficient of thermal expansion (CTE) measurement of different aerospace materials. The CTE of a composite is different from that given by a simple rule of mixtures. This is because of the presence of reinforcement. The expansion coefficient of reinforcement is less than that of the matrix which introduces a mechanical constraint on the matrix. The degree of constraint is also dependent on the nature of the reinforcement. It is important to point out that interface can exert some influence on the value of CTE, especially for very small particle size. In addition to the interface, the CTE of particle reinforced metal matrix composites (MMCs) is affected by several other factors. To cater the needs of various requirements in a spacecraft making, a wide variety of materials are used. Besides, the indigenization efforts and development of new materials for space-use emphasizes the measurement of CTE before their actual use. Stir casting technique was used to fabricate composites containing Si Cp as reinforcements and special thermo physical properties of the material are found. CTE of the composites are measured by TMA. The experiments have been carried out in the temperature range -1400 C to 5750 C.