Damage mechanics and energy absorption capabilities of naturalfiber reinforced elastomeric based bio composite for sacrificial structural applications

The present study deals with the experimental, finite element (FE) and analytical assessment of low ballistic impact response of proposedflexible'green' composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute (JRJ), jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ). Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime. The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism. Results revealed that inclusion of natural rubber aids in better energy ab-sorption and mitigating the failure of the proposed composite. Among the three different stacking se-quences of flexible composites considered, JRJRJ provides better ballistic performance compared to its counterparts. The damage study reveals that the main mechanism of failure involved in flexible com-posites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposedflexible composites are free from catastrophic failure. Results obtained from experimental, FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other. The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.     

A novel formulation of material nonlinear analysis in structural mechanics

This article demonstrates a novel approach for material nonlinear analysis. This analysis procedure eliminates tedious and lengthy step by step incremental and then iterative procedure adopted classically and gives direct results in the linear as well as in nonlinear range of the material behavior. Use of elastic moduli is eliminated. Instead, stress and strain functions are used as the material input in the analysis procedure. These stress and strain functions are directly derived from the stress-strain behavior of the material by the method of curve fitting. This way, the whole stress-strain diagram is utilized in the analysis which naturally exposes the response of structure when loading is in nonlinear range of the material behavior. It is found that it is an excellent computational procedure adopted so far for material nonlinear analysis which gives very accurate results, easy to adopt and simple in calculations. The method eliminates all types of linearity assumptions in basic derivations of equations and hence, eliminates all types of possibility of errors in the analysis procedure as well. As it is required to know stress distribution in the structural body by proper modelling and structural idealization, the proposed analysis approach can be regarded as stress-based analysis procedure. Basic problems such as uniaxial problem, beam bending, and torsion problems are solved. It is found that approach is very suitable for solving the problems of fracture mechanics. Energy release rate for plate with center crack and double cantilever beam specimen is also evaluated. The approach solves the fracture problem with relative ease in strength of material style calculations. For all problems, results are compared with the classical displacement-based liner theory.     

Study on energy release characteristics of reactive material casings under explosive loading

Reactive Materials (RMs), a new material with structural and energy release characteristics under shock-induced chemical reactions, are promising in extensive applications in national defense and military fields. They can increase the lethality of warheads due to their dual functionality. This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading. Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs, temperature distribution, peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material (RM) warhead casings by using high-speed camera, infrared thermal imager temperature and peak overpressure testing and scanning electron microscope. Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings. The RM casings can improve the peak overpressure of the air shock wave under explosion loading, though the results are different with different charge ratios. According to the energy release characteristics of the RM, increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave, while reducing the thickness will increase the peak overpressure of the far-field air shock wave.     

INTEGRATING NUCLEAR WEAPONS STOCKPILE MANAGEMENT AND NUCLEAR ARMS CONTROL OBJECTIVES TO ENABLE SIGNIFICANT STOCKPILE REDUCTIONS

In his 2009 Prague speech and the 2010 Nuclear Posture Review, President Barack Obama committed the United States to take concrete steps toward nuclear disarmament while maintaining a safe, secure, and effective nuclear deterrent. There is an inherent tension between these two goals that is best addressed through improved integration of nuclear weapons objectives with nuclear arms control objectives. This article reviews historical examples of the interaction between the two sets of objectives, develops a framework for analyzing opportunities for future integration, and suggests specific ideas that could benefit the nuclear weapons enterprise as it undergoes transformation and that could make the future enterprise compatible with a variety of arms control futures.     

PREVENTING DIRTY BOMBS

Radioactive sealed sources have a long history and a much wider worldwide distribution than do weapons-usable fissile materials. This article compares the mechanisms for controlling radioactive sources with those of weapons-usable materials and makes the case for improved policy making on the safe and secure management of radioactive sources (often referred to simply as “sources”). Such sources have been widely distributed with commercial and government support to nearly every country, yet there are no legally binding, international agreements or regulations to control any aspect of their life cycle. This is problematic because some sources that are disused, abandoned, or otherwise fall out of regulatory control could be used in the form of a radiological dispersal device (RDD, or dirty bomb). An RDD could pose significant economic and psychological impacts with the potential for detrimental effects on public health. The lack of international measures to control sources is troubling for several reasons: creating an RDD is much easier than fashioning a nuclear weapon from scratch or from stolen fissile materials; given the many incidents involving diversion from regulatory control and the misuse of sources, an RDD attack would be one of the more likely scenarios; materials security for sources is generally weak and inconsistent; it is nearly impossible to determine the total amount of sources manufactured and distributed; used sources are frequently found uncontrolled and transiting borders, and penalties are light at best; the market-based supply and demand of sources facilitates their rapid and loosely regulated distribution; and the “peaceful uses” aspect of the Treaty on the Non-Proliferation of Nuclear Weapons along with norms that began developing around the time of Atoms for Peace have promoted the nearly unchecked global distribution of sources. Several immediate and long-term actions are suggested to reduce the threat posed by radiological sources.     

Deferred verification: verifiable declarations of fissile-material stocks for disarmament purposes

ABSTRACT

Nuclear disarmament is often seen as eventually requiring access to nuclear warheads or to the warhead-dismantlement process to verify that a state has not hidden weapons or weapon-materials despite promising to disarm. This article suggests this view is misplaced, and that what is needed is a verification mechanism able to provide reliable assurances of the absence of fissile materials available for use in weapons after a state has disarmed. Such a mechanism will need an initial declaration of the amount of fissile materials held by a state for all purposes, military and civilian. In a state with a nuclear arsenal awaiting elimination, this declaration would have to include materials that may not be available for verification because they are in nuclear weapons or are in other classified or proliferation-sensitive forms. This article describes a verification arrangement that does not require access to materials in weapons and in sensitive forms while still allowing checks on the overall accuracy of the declaration. Verification of the completeness and correctness of the declaration is deferred to the time when the weapons-relevant material enters the disposition process, at which point it no longer has any sensitive attributes. By removing the focus on monitoring warheads and dismantlement, this new approach could provide a more manageable path to nuclear disarmament.     

The Importance of Safeguards Culture

International safeguards is the system of measures put in place by the International Atomic Energy Agency and states to ensure nuclear programs remain dedicated to peaceful purposes. This international safeguards system consists of agreements, inspections, and evaluations that have never considered the safeguards culture of a state or facility. Neither a common definition nor an understanding of safeguards culture is internationally recognized. This article provides an analysis of the concept of safeguards culture and gauges its value to the international safeguards community. The authors explore distinctions among safeguards culture, safeguards compliance, and safeguards performance, and suggest possible indicators of safeguards culture and methods to promote a strong, positive safeguards culture.     

The Hydrogen Bomb,Lewis L. Strauss and the Writing of Nuclear History

In January 1950 President Harry S. Truman announced that the United States would proceed with further work to determine the feasibility of a ‘Super’, or hydrogen, bomb. The events leading up to that decision – counter-pressures and advocacy from a number of quarters, including the divided Atomic Energy Commission (AEC), the nuclear scientists, Congress and the Pentagon – is well known. Less attention has been given to how the story of the Super came to be told in official and popular publications. Admiral Lewis L. Strauss, rogue member of the AEC, later presidential adviser on atomic affairs and AEC chairman, was one of the most vigorous advocates of developing thermonuclear weapons. He was also a highly skilled player of bureaucratic politics. This article draws upon the Strauss archives to examine how he used his position and his contacts to shape the history of the H-bomb to his own political advantage.     

制冷系统节能目标函数的研究

本文分析传统采用制冷系数(EER)作为节能指标的不准确性,提出采用(?)效率作为衡量制冷装置在不同工况下运行的节能指标。从(?)效率定义出发推导出带回热的制冷系统的(?)效率关系式,这为寻找装置最佳运行工况提供理论依据,并通过实验证实了理论的分析。     

Serious Rules for Nuclear Power Without Proliferation

The authors propose five principles for addressing the major deficiencies of the current treaty-based approach to nonproliferation. These involve: effectively closing the door to withdrawals from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT); defining which nuclear technologies fall within the NPT's “inalienable right” provision, so as to maintain a reasonable safety margin against possible military application; expansion of International Atomic Energy Agency inspections to include greater readiness to use its “special” inspection authority; creation of an NPT enforcement regime, to include a secretariat; and universalizing the NPT so as to apply to all states, while creating a path for current non-parties to come into compliance. There is no illusion here about the prospects for the adoption of this approach. At a minimum, the world needs to be frank about the gap between nuclear programs and current nonproliferation protection. Encouragement of greater use of nuclear power should be predicated on closing that gap.