Effects of ultrasonic impact treatment on pre-fatigue loaded high-strength steel welded joints

Comparative fatigue tests were conducted on as-welded, weld toe peened specimens before and after fatigue loading. Fracture surface, residual stress, microstructure and hardness were determined. The test results showed that as the pre-fatigue loading period extended, deeper cracks may have initiated and propagated and the fatigue life improvement decreased. The processes of ultrasonic peening on welded joints with existing cracks were modeled by finite element analysis. The numerical results indicated that the mechanism of UIT improving fatigue performance included two factors: compressive residual stress and the change of crack orientation. Both effects reduced as the crack became deeper.     

Stress-deformable state of isotropic double curved shell with internal cracks and a circular hole

This work is devoted to the stress–strain state of isotropic double curved shell with defect system. The construction is weakened by two non-through thickness (internal) cracks of different length and by a circular hole located between cracks. In this study we use the line-spring model. Within the framework of this model cracks are modeled as mathematical cuts of shell’s middle surface. This leads to a two-dimensional problem. The problem is reduced to a system of eight boundary integral equations. To ensure the uniqueness of solution an additional equation is added. In the numerical solution of the problem special quadrature formulas for singular integrals of Cauchy type and the finite difference method are applied. The influence of defects on each other for double curved shell has been investigated. The given theoretical results can be used for the calculation of structural elements with holes, cracks on the strength and fracture toughness in various branches of engineering.     

某河床式水电站溢流坝裂缝分析处理

混凝土坝裂缝的预防和控制是混凝土坝工程设计和施工的重点研究课题,每个工程混凝土裂缝发生的部位和数量各不相同,裂缝的成因也不尽相同,只有分析清楚裂缝的成因和危害才能采取相应的措施进行预防和解决.本文对某河床式水电站溢流坝闸墩和堰面裂缝的成因和危害进行了详细的分析,针对性地提出了裂缝处理方案和后续预防措施.电站溢流坝闸墩及堰面裂缝经处理后已有裂缝已封闭,后续混凝土浇筑未见新的裂缝产生,目前工程已安全运行十多年.     

PHC管桩静压成桩过程中裂缝产生原因及预防

本通过对某厂房工程基础PHC管桩在静压成桩过程中，产生不规则裂缝的现象，分析其原因，提出了预防裂缝产生的措施。     

商品混凝土裂缝案例分析与研究

结合某商品混凝土公司遇到的几个混凝土工程案例的裂缝问题,分析了混凝土裂缝产生的原因,提出的相应预防处理措施,可有效控制和减少混凝土裂缝的产生,并为类似工程提供借鉴。     

Study on reinforced lightweight coconut shell concrete beam behavior under torsion

This research investigates and evaluates the results of coconut shell concrete beams subjected to torsion and compared with conventional concrete beams. Eight beams, four with coconut shell concrete and four with conventional concrete were fabricated and tested. Study includes the general cracking characteristics, pre cracking behavior and analysis, post cracking behavior and analysis, minimum torsional reinforcement, torsional reinforcement, ductility, crack width and stiffness. It was observed that the torsional behavior of coconut shell concrete is comparable to that of conventional concrete. Compare to ACI prediction, equation suggested by Macgregor is more conservative in calculating cracking torsional resistance. But for the calculation of ultimate torque strength ACI prediction is more conservative compared to the equation suggested by Macgregor. Indian standard is also conservative in this regard, but it was under estimated compared to ACI and Macgregor equations. Minimum torsional reinforcement in beams is necessary to ensure that the beam do not fail at cracking. Compared to conventional concrete specimens, coconut shell concrete specimens have more ductility. Crack width at initial cracking torque for both conventional and coconut shell concrete with corresponding reinforcement ratios is almost similar.     

An array waveguide probe for detection,location and sizing of surface cracks in metals

The paper describes the development of a novel microwave probe for detection, location and sizing of surface cracks in metals. The probe utilizes the inherent mutual coupling in an array structure to determine crack alignment, placement and dimensions. The main feature of the probe is its ability to electronically scan the region of concern, thus avoiding the large inspection time and unwanted noise experienced in the conventional mechanical scanning. Theoretical and experimental results are presented for a prototype two-cell array probe when scanning a metallic specimen containing a long surface crack. It is shown that the probe is capable of determining the orientation, location and dimensions of surface cracks of a few millimeters depth.     

Seismic stability analysis of gravity retaining wall supporting c–φ soil with cracks

This article presents an analytical approach for the seismic stability analysis of gravity retaining wall with c–φ backfill soil. Cracks which are pre-existing (open before the collapse) and are form as part of slope collapse are considered. For a translational failure mechanism assumed, formulas are provided to calculate directly the yield acceleration and the inclination of failure surface. Factors such as cracks and cracks opening, wall back inclination, soil-wall friction, backfill slope are easily to be coupled into the formulations. Both the depth and most adverse location of the crack can be determined from the optimization procedure. Comparisons are made with existing methods and the influences of cracks opening are discussed. The influence of a crack presence on seismic stability of soil-wall system is distinct and pre-existing (opened) cracks have more adverse effect.     

Evidence of gas permeation in electrostatically painted steel cylinders

The process of gas generation, entrapment and subsequent permeation through coatings applied on the surface of metals for corrosion protection purposes is the cause for the development of a defect known as “fish-scaling”. Particularly, in operations like enamelling or painting of metals, this phenomenon affects strongly the surface quality of the items and the development of further processing operations. In this work, the reasons that promote the development of defects in electrostatically painted steel during the manufacture route of fire extinguishers are analysed. The surface and cross section analyses of the samples conducted by optical and scanning electron microscopy suggest that the degradation of the coating is caused by gas migration from the metal-coating interface to the surface of the cylinders. Water used during cleaning and descaling operations acted as a potential gas source being hydrogen the element responsible for the formation of both, structural defects in the coating and cracks in the steel substrate. The degradation mechanisms of the steel and the coatings are found and explained in terms of manufacturing process of the cylinders.     

Non-destructive evaluation of cracks in massive concrete using normal dc resistivity logging

Discontinuities are one of the most harmful damage to the durability of concrete structures. Currents approaches are limited to assessments of surface damages, even if non-destructive methods appear to be effective for the detection and the location of cracks. That is why, these methods might be unsuitable for investigation of massive concrete body as dams and locks. Present works aim at the presentation of new results with electrical resistivity to study damages within concrete structures. In this article, the electrical resistivity focused on the study of cracks and discontinuities (concrete joints, interfaces…) in massive concrete structures by measurements done in preexisting boreholes. The used array is the normal dc resistivity logging. The study presents numerical and experimental results. First, modeling allows correcting experimental data. Then, development shows the sensitivity relatively to the discontinuity characteristics (aperture and the resistivity contrast between the discontinuity and the concrete). The tests on a real structure are carried out to define the methodology for on-site measurement. Results support the modeling.