Joint width

Another aluminum effect which appears to be age-related is skeletal toxicity. Increased carpal joint width, suggestive of poor bone calcification, was observed in immature rabbits receiving 20 subcutaneous doses of aluminum lactate, but was not seen in neonatal or adult rabbits (Yokel 1987). 

Figure 6.76 Experimental safe gap values w of gas-air mixtures (referring to an initial pressure p0 = 1.0 105 Pa) versus joint width L.

Joint width / = 25 mm Arcing chamber volume 0.1 m3 Voltage 500 V rms Short-circuit current 5 kA rms. Arc burning in pure air (filled dots) or in 9% (v/v) CH4-air mixtures (blank dots). Indicating chamber filled with 9% (v/v) CH4-air mixture. 

The average shore A hardness of the cured sealant is 20 to 25 but increases with ageing. Resistance to ultraviolet radiation is excellent, but this is not important for indoor applications. The maximum movement accommodation factor (MAF) can be 15% of the total joint width. Joints should be designed so that movement due to shrinkage and thermal changes does not exceed the maximum MAF, related to the joint width. Table 5.4 lists the properties in general for acrylic emulsion sealants. These properties are summarised from the commercial literature of several acrylic emulsion sealant manufacturers and should not be considered as specifications. Table 5.5 lists the standard specifications for these sealants. 

Low-modulus sealants are usually preferred when the joint elongation is high (over 25% of joint width) whereas high-modulus sealants are chosen for assembly where the elastic movement under strain is reduced to a minimum (Houde, 1993). Table 6.6 gives the properties and applications of silicone sealants depending upon their modulus. 

The cured sealant gives a tough, elastic, rubber-like seal and gives excellent adhesion to concrete and masonry, glass, aluminium and stainless steel. The shore A hardness ranges from 15-35. The movement accommodation factor is 25% in butt joints and 50% in lap joints. These sealants have the capacity to accommodate continuous and pronounced cyclic movements. They are suitable for joints where the joint width may range between 5 mm and 50 mm. Joints which are expected to experience cyclic movements should have a width depth ratio of 2 1. Minimum sealant depths recommended for different environments are mentioned in Table 7.8. Primers... 

Underwater functional joints are filled with UTK-M composition and if the joint width varies considerably, polyester cloth impregnated with UTK-M is glued on. 

Besides durability, premium sealants are judged by special properties as shown in Table 4. The ability to take on greater elongation and compression is measured by movement capability in terms of joint width. The stability to UV exposure is important for those glazing and insulation compounds used in modern high-rise structures. Thermal stability is in demand for solar collectors, or for other structural materials. On the basis of these evaluations, we can foresee future trends of sealants as shown in Table 4. Silicones appear to out-perform others. In the meantime, technical advances will provide low-modulus polysulfides, and better movement ability for both polysulfides and polyurethanes. Their cure time will be decreased and the UV stability will be improved to match or compete with silicones. All three will be developed for better adhesion under the un-primed conditions. 

Figure 7.20 Dependence of shear strength on bond width and bond overlap. Strength increases linearly with increasing joint width. The increase in strength with increasing overlap is gradual after a particular overlap is reached, there is no further increase in joint strength. ...

When calculating the design width of joints in a building, it is essential to take account of the tolerances on the relevant dimensions of the components and the accuracy in placing them that is likely to be achieved on site. For these reasons, there may, in practice, be considerable variation in the widths of a number of ostensibly identical joints. The joint width for the design must ensure that in no joint will the sealant be subjected to a level of compression or extension that, when expressed as a proportion of the achieved joint width, exceeds its movement capability. (See the Selection of joint sealants, where Table 1 gives maximum movement permitted for each major type of sealant.) However, considerable variation in formulation and properties may occur between different brands of the same chemical type, which may affect this value. The maximum tolerable joint movement quoted by the manufacturer should be used in joint design calculations. 

A simple formula for the calculation of joint width has been derived. The minimum joint width achieved must be sufficient to allow the sealant to be effectively gunned... 

A large variety of different sealant products are available, ranging from plastomeric oil-based mastics that are little more than joint fillers, to high-performance elastomeric sealants, which are capable of withstanding large joint movements of np to 60% of the nominal joint width. 

When the amplitude of joint movement is likely to be 20% or more of the joint width, it is essential to use one of the elasto-plastic or elastic types of elastomeric sealant. 

Movement relative to Adhesive layer thickness and sealing joint width Thermal movement (e.g. very slow quasi-static) Loading and unloading Slight accident, infrequent incidents (e.g. derailment) Normal service operation (dynamic, fast)... 

Czamocki and Piekarski s) used a nonlinear elastic stress-strain law for three-dimensional failure analysis of a symmetric lap joint. Taking into account the variation of Poisson s ratio with strain within the adhesive, the authors concluded that the failure of the adhesive layer originates in the central plane of a joint (at the front edge). It was also observed that the joint width did not have any effect on the stress peaks in the central plane and that the application of a weaker but more flexible adhesive resulted in higher load-carrying capacity and lower stress concentrations in the adherends. 

Chip Components. Side overhang is acceptable up to one-half (one-quarter for Class 3) the width of the component end cap or PCB pad. End-cap overhang is not acceptable for all classes. The end-cap solder joint width is acceptable with a minimum solder joint length of one-half (three-quarters for Class 3) the component end cap or PCB land, whichever is less. 

Minimum End Joint Width C Wetting is evident 50% (W) or 50% (P), whicheyer is less ... 

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