Failure of Joints

There has, however, been concern raised over the stability of the CAA oxide on Ti6A14V when exposed to dry conditions for prolonged periods (up to 1200 h) at 330 °C or shorter periods (up to 24 h) at 400 °C. A brittle zone has been shown to form at the oxide-metal interface, which results in cohesive failure of joints at low loads, below 0.7 MPa, when measured in a tensile butt test. Cohesive failure in this instance occurred within this brittle zone. 

For the KFUPM specimen designed with relatively high reinforcement ratio p = 0.01 (J-Bl-18), experimental results showed that the specimen collapsed due to failure of joint under shear, as the joint collapse load was lower than the flexural capacity of the beam (27.6 % lower). That was confirmed from the combined mechanistic/experimental computations and also further corroborated from DIANA results. 

Zhang Hou-quan, Chang Xu, Tang Chun-an et al. Numerical study on shear failure of jointed rock with several flaws under shear testing [J]. Chinese Journal of Rock Mechanics and Engineering, 2005, 24(supp) 5136-5140. 

The issue with the strengthening of beam-column joints is extensively described in the draft of the Guidelines for Reparation and Strengthening of Structural Elements, Curtain Walls and Partitions edited by the Department of Civil Protection and by the ReLUIS consortium in August 2009 that highlights that the majority of failures of joints and of the requests for ductility in columns is usually localized in the exterior joints and columns, particularly those in the comers, for the following reasons ... 

Reference should also be made to recent work relating to the failure of joints due to fatigue stressing. Chen, Niem, and have studied the fatigue life of both plastic-to-plastic and... 

The use of a bypass is not permitted since this adds to the risks of failure of joints and valves. In any case the use of a bypass to assist trip testing creates a potentially false result since the supply line pressure is not imposed on the closing valve. It is ability of the ESDV to close against full flow of the pipeline under pressure that is one of its essential features. 

Chemical bonding between adhesive and adherend. Failure of joint within the glue line. 

Heat for soldering is usually obtained from torches. The high conductivity of copper makes it necessary to use large flames for the larger sizes, and for this reason the location in which the joint will be made must be carefully considered. Soldered joints are most widely used in sizes 2 in and smaller for which heat requirements are less burdensome. Soldered joints should not be used in areas where plant fires are hkely because exposure to fires resiilts in rapid and complete failure of the joints. Properly made, the joints are completely impervious. The code permits the use of soldered joints only for Category D fluid service and then only if the system is not subject to severe cychc condions. 

Because of the inherently greater susceptibility of expansion bellows to failure from unexpected corrosion, failure of guides to control joint movements, etc., it is advisable to examine critically their design choice in comparison with a stiff system. 

As discussed in Section 29.2.5, jointing of two different metals (copper being one) causes electrolysis at the joints, leading to corrosion and failure of the joint. To avoid this, it is recommended that the same procedure be adopted as discussed in Section 29.2, and where the electrode and the connecting ground strip are of the same metal, that the joints are riveted or welded with the same metal after making the surface. Soldering is not recommended. 

The path of failure of an adhesive joint can give information about the mechanism of failure if analysis of the elemental and chemical composition can be conducted along the path. Several authors have performed such analyses by loading the adhesive joint until it fractures and then using XPS to analyze each side of the fracture. 

The principal failure modes of bolted joints are (1) bearing failure of the material as in the elongated bolt hole of Figure 7-44, (2) tension failure of the material in the reduced cross section through the bolt hole, (3) shear-out or cleavage failure of the material (actually transverse tension failure of the material), and (4) bolt failures (mainly shear failures). Of course, combinations of these failures do occur. 

Fractures, fissures, and joints are openings in sedimentary rocks formed by the structural (mechanical) failure of the rock under loacls caused by earth crust tectonics. This form of porosity is extremely hard to evaluate quantitatively due to its irregularity. 

The corrosion fatigue failure of total joint prostheses has been widely studied. It can be concluded from an extensive literature survey carried... 

Rose, R. M., Schiller, A. L. and Radin, E. L., Corrosion-Accelerated Mechanical Failure of a Vitallium Nail-Plate , Journal of Bone and Joint Surgery, 54A, 854-862 (1972)... 

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

Although the problems associated with the corrosion and protection of jointed structures have been recognised since the early days of structural fabrication, they have taken on a special significance in the past 15 years. The motivation for the increased impetus is mainly one of concern over possible costly, hazardous or environmentally unfriendly failures particularly those concerned with offshore constructions, nuclear reactors, domestic water systems, food handling, waste disposal and the like. 

In the majority of stoneware constructions some form of joint has to be provided, and in runs of piping there will be very many joints, which frequently fail owing to failures in the jointing material. It is essential that all... 

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