Connection design Mechanical joints

Joint category—Ciassifrcation used on the highest hierarchic level of the connection design to indicate the load transfer mechanism from one member to another. 

P(l) This section covers the design of mechanical joints where at least one of the primary components to be joined is made of glass FRP. Such joining techniques include fastener connections, friction joints (shear loads), contact joints (direct loads), threaded joints, strap joints and joints incorporating embedded fasteners (see 5.i.4 P(2)). 

Safe and proper performance of compressed gas systems depends on the integrity of the many mechanical joints between system components. The proper design and use of mechanical connections is of utmost importance to the safety of personnel, equipment, and plant operations. 

Furthermore, a cell header with its 70-100 connections is not easy to replace, and considerable numbers of safety features have to be incorporated into its design. Composite materials do not lend themselves to effective non-destructive testing and a leaking joint may lead to delamination of the chemical-resistant liner from its mechanical support. Since any leaks cannot be detected easily in such circumstances, the entire header must be replaced with a corresponding electrolyser downtime. 

If the insert is loaded in the in-plane direction of the sandwich component, the connection is defined to he mechanically interlocked and shall be designed as an embedded insert Joint. 

Bonded inserts are also commonly used in sandwich structures, most typically in panels. The insert is bonded into the core and to one or both skins of the sandwich. Loads are then directed to the joint through the mechanical fasteners (i.e. the insert) in their axial direction, causing out-of-plane loading of the sandwich component. Sandwich structures typically have thin skins and therefore the loads from the insert are mainly transferred to the core. If the insert is loaded in the in-plane direction of the sandwich member, the connection is categorised as an embedded insert and it should be designed as a mechanical connection. 

If appropriate fittings are not available in the same material as the pipe it then becomes necessary to use fittings in an alternative material and then some care must be exercised in the design of transition connection. For example, before plastic valves which could be welded to PE pipes became available it was necessary to employ metal valves with a mechanical connecting joint. 

PVC pipes can be solvent welded but mostly they are joined by mechanical compression or push-fit connectors. Various designs exist and the most successful are capable of connecting any type of pipe within specified diameter range. Some mechanical fittings for softer materials such as PE use compression of the pipe wall into grooves as a means of sealing the joint. This technique is unsuited to harder plastics such as PVC. The multiple application connectors rely upon compression of a separate elastomeric seal. 

Bonded joints are extensively employed in the construction of composite structures in aerospace applications, maritime structures, lifting equipment, wind mills as well as automotive industries [3, 4, 5], Unlike the bolt hole in mechanical fastening that causes a stress concentration in the composite joint plates, adhesively bonded joints minimize the potential for stress concentration within the joint. Besides, applications where lower structural weight, improved damage tolerance design philosophy are required, adhesively bonded joints provides a potential solution. Bonded joints are an efficent fastening solution also for hybrid structures, i.e., structures where composite parts are connected to metal parts. 

Correct joint design is crucial and needs to take into account the specific mechanical properties of the substrates and the adhesives used. Simply substituting elastic adhesives for rigid fastening - such as a riveted connection - will not always achieve the desired result. 

The considerably improved mechanical properties of SIFCON can be exploited in various structures or in their particular regions, where locally improved properties may modify overall structural behaviour, such as shields against projectiles or radiation, repair of outdoor structures, joint connections in structures exposed to seismic action or possible explosions, pre-cast impact resistant panels, walls of treasuries, etc. The practical applications of SIFCON are restricted to these special structures probably there are some barriers on information about executed structures and details of their design, and such restrictions are compulsory for both designers and contractors. Also, the question as to whether the high additional costs of materials and construction are balanced by the performance of the product should be answered in every case. 

Connections. Mechanical connections, in joints and terminals, should be designed to clamp conductors firmly and not slacken in service. Maintainability. Connections that have to be periodically inspected and tested, such as earthing connections, should be readily accessible. Ventilation. There should be adequate ventilation, or enclosures should be so designed that overheating does not occur. 

---