[en] The reliability of pressure piping containing defects is important in engineering. The failure probability of pressure piping containing defects may be used as a guide to the most economic deployment of resources on maintenance, inspection and repair. This paper presents a probabilistic assessment methodology for in-service pressure piping containing defects, which is especially designed for programming. It is based on three assessment codes, BS 7910, R6 and SAPV-99, considering uncertainties in operating loadings, flaw sizes, material fracture toughness and flow stress. A general sampling computation method of stress intensity factor (SIF), in the form of the relationship between SIF and axial force and bending moment and torsion, is adopted. This relationship has been successfully used in developing software, Safety Assessment System of In-service Pressure Piping Containing Flaws (SAPP-2003), to assess planar and non-planar flaws. A numerical example is presented to illustrate the application of SAPP-2003 for calculating the failure probabilities of separate defects and for the assessed pressure piping

[en] Failure analysis of in-service nuclear piping containing defects is an important subject in the nuclear power plants. Considering the uncertainties in various internal operating loadings and external forces, including earthquake and wind, flaw sizes, material fracture toughness and flow stress, this paper presents a probabilistic assessment methodology for in-service nuclear piping containing defects, which is especially designed for programming. A general sampling computation method of the stress intensity factor (SIF), in the form of the relationship between the SIF and the axial force, bending moment and torsion, is adopted in the probabilistic assessment methodology. This relationship has been successfully used in developing the software, Safety Assessment System of In-service Pressure Piping Containing Flaws (SAPP-2003), based on a well-known engineering safety assessment procedure R6. A numerical example is given to show the application of the SAPP-2003 software. The failure probabilities of each defect and the whole piping can be obtained by this software

[en] By taking account of the high-order corrections to the paraxial approximation of a Gaussian beam, it has been verified that for a focused laser beam propagating in vacuum, there indeed exists a subluminous wave phase velocity region surrounding the laser beam axis. The magnitude of the phase velocity scales as V_φm∼c(1+b/(kw₀)²), where V_φm is the phase velocity of the wave, c is the speed of light in vacuum, w₀ is the beam width at focus. This feature gives a reasonable explanation for the mechanism of capture and acceleration scenario

[en] It has been found that for a focused laser beam propagating in vacuum, there exist 'natural' channels for laser driven electron acceleration, which emerge just beyond the beam width and extend along the diffraction angle for a few Rayleigh lengths. These channels have the similar characteristics to that of a wave guide tube of conventional accelerators: a subluminous wave phase velocity in conjunction with a strong longitudinal acceleration electric field. Relativistic electrons injected into these channels can be captured in the acceleration phase of the wave for sufficiently long time and gain considerable net energy from the laser field. The basic conditions for this acceleration scheme to emerge are addressed here

[en] An acceleration channel has been found in the field of a focused laser beam propagating in vacuum, which shows similar characteristics to that of a wave guide tube of conventional accelerators: a subluminous wave phase velocity in conjunction with a strong longitudinal electric field component. Relativistic electrons injected into this channel can remain synchronous with the accelerating phase for sufficiently long time and receive considerable energy from the field. We call this acceleration scheme CAS (capture and acceleration scenario). The basic conditions for CAS to occur are examined and the output properties of electrons accelerated by this scheme are also presented in this paper

[en] In this paper we present a comparison between the effects on electron dynamics by a linearly polarized and a circularly polarized field of an intense laser beam. Special attention is given to the vacuum laser acceleration scheme, also known as capture and acceleration scenario (CAS). It has been found that CAS phenomenon can occur in both polarized fields but there are differences. The CAS of a circularly polarized field exhibits axisymmetric feature, whereas CAS of a linearly polarized field can only be observed when electrons are injected nearly along the polarization plane. Given the same laser parameters (intensity, beam width), the maximum energy gained by the electrons from linearly polarized field is higher than that from circularly polarized field. Physical explanations based on the space distributions of the field amplitudes are described. We hope this study provides significant help to those designing experimental setup to verify CAS as well as to those developing laser accelerators of the future

[en] The correlation between the outgoing energy and the scattering angle of electrons accelerated by a laser beam in vacuum has been investigated. Essentially, the single-valued function of the correlation, derived from classical electrodynamics Compton scattering for a plane wave, is broadened to a band. It means electrons with the same outgoing energy will have an angular spread. An equation to describe this correlation has been derived. Dependence of the spread width of scattering angle on laser beam parameters is examined, and physical explanations of these features are given. The results are found to be consistent with the simulation results for a proposed vacuum laser acceleration scheme: the capture and acceleration scenario

[en] In this paper, we have studied the dynamic characteristics of relativistic electron injected into stationary intense vacuum laser fields. We found the dynamic trajectories can basically be classified as three categories, namely Inelastic Scattering (IS), Capture and Acceleration Scenario (CAS) and Penetrate into Axial Region and Move (PARM) trajectory. The physical mechanism as to the three kinds of electrons have been examined. In particular, the PARM trajectory which we presented in this paper is different from the CAS and IS trajectory which we had already found in our previous work. We will show the PARM stems from the strong diffraction effect of a tightly focused laser field. In addition, the initial condition for the three kinds of electrons to emerge were detailed investigated. It has been found that there are four factors which chiefly decide the appearance of the three kinds of dynamics trajectories, namely the laser beam width w₀ and intensity a₀, the electrons incident angle θ and initial transversal momentum p_ti. The implication of the PARM electrons to the planned vacuum laser accelerators is illustrated

[en] The three-segment fitting method is presented to describe the material stress-strain curves with yield plateaus. A J integral estimation approach for carbon steel piping with circumferential through-wall cracks was developed. Failure assessment curves obtained using three options in the CEGB R6 approach were proposed for GB20 carbon steel piping under bending. The initiation and maximum moments predicted by the J estimation approach presented in this paper are quite close to the experimental values. (orig.)

[en] As an important parameter of fracture criterion, stress intensity factor (SIF) is considered to be one metric of the singular stress field intensity near the crack tip, also a main parametric in fracture mechanics. Therefore, solving technique on the stress intensity factor takes an important role in engineering applications. In view of typical three-dimensional features of flat-oval thin-walled pipes, it is relatively tough to obtain the stress intensity factors for the special-shaped shells with multi-transverse cracks by classical methods. In this paper, a very simple method based on J₂-integral and bending theory is proposed to calculate the SIFs. Examples demonstrate that this technique is feasible, especially, that, suitable for the determination of the stress intensity factors of three-dimensional complicated structures. And the results show that not only the solution process is simple and available, but also the closed-form solutions can be derived effectively.