Load bearing

Welded structures often have to be tested nondestructively, particularly for critical application where weld failure can he catastrophic, such as in pressure vessels, load-bearing structural members, and power plants. 

Control of quality and state of engine parts, components of electric, pneumatic, hydraulic systems, load-bearing elements Investigations of parts and units failure causes... 

Bowden and Tabor [4] cite support for the general idea that film molecules are forced to a horizontal configuration in load-bearing regions and the general idea was proposed by Wilson in 1955 [63]. 

SAN resins possess many physical properties desked for thermoplastic appHcations. They are characteristically hard, rigid, and dimensionally stable with load bearing capabiHties. They are also transparent, have high heat distortion temperatures, possess exceUent gloss and chemical resistance, and adapt easily to conventional thermoplastic fabrication techniques (7). 

Table 1 provides the approximate load bearing capabiUties of various adhesive types. Because the load-bearing capabiUties of an adhesive are dependent upon the adherend material, the loading rate, temperature, and design of the adhesive joint, wide ranges of performance are Hsted. 

Load bearing capabiUties are dependent upon the adherend, joint design, rate of loading, and temperature. Values given represent the type of adherends normally used at room temperature. Lap shear values approximate those obtainable from an overlap of 3.2 cm. ... 

The sandwich-type stmcture of polyurethanes with a smooth integral skin produced by the reaction injection molding process provides a high degree of stiffness as weU as exceUent thermal and acoustical properties necessary for its use in housing and load-bearing stmctural components for the automotive, business machine, electrical, furniture, and materials-handling industry. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

In addition to the soHd form of natural mbber it is available as a soHd suspended in water, known as latex. Synthetic mbbers are also available in latex form. Latex has become an important commodity used in the manufacture of dipped goods for health and disease protection. The principal uses of natural mbber are as follows tires and retreading, 70% latex (gloves, balloons), 12% mechanical goods, 9% load-bearing components, 4% and other, 5%. 

Activators. Activators are chemicals that increase the rate of vulcanization by reacting first with the accelerators to form mbber soluble complexes. These complexes then react with the sulfur to achieve vulcanization. The most common activators are combinations of zinc oxide and stearic acid. Other metal oxides have been used for specific purposes, ie, lead, cadmium, etc, and other fatty acids used include lauric, oleic, and propionic acids. Soluble zinc salts of fatty acid such as zinc 2-ethyIhexanoate are also used, and these mbber-soluble activators are effective in natural mbber to produce low set, low creep compounds used in load-bearing appHcations. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. 

Sihcone oils are good hydrodynamic lubricants but have generally poor frictional lubricating properties (352—354). The latter can be improved by incorporating chlorophenyl groups into the polymer side chains (355). For steel on steel, the coefficient of friction is about 0.3—0.5. The load-bearing capacity of PDMS (Almen-Wieland machine) is only 50—150 kg, compared with - 1000 kg for polychlorophenyLmethylsiloxane and up to 2000 kg for mineral oil. 

The design of load-bearing structures for service at room temperature is generally based on the yield strength or for some appHcations on the tensile strength. The metal is expected to behave essentially in an elastic manner, that is, the stmcture undergoes an elastic deformation immediately upon load apphcation and no further deformation occurs with time. When the load is removed, the stmcture returns to its original dimensions. 

The principal commercial uses of sulfur monochloride are in the manufacture of lubricant additives and vulcanising agents for mbber (147,154,155) (see Lubrication AND lubricants Rubber chemicals). The preparation of additives for wear and load-bearing improvement of lubricating oils is generally carried out in two steps and the technology is described in numerous patents (155) (see Sulfurization and sulfchlorination). 

Thermal and Chemical Stability. In addition to load-bearing properties, tire reinforcement must be able to resist degradation by chemicals in cured mbber and heat generation. The most critical degradant depends on the material in use. Most thermoplastic reinforcements are either modified directiy or stabiH2ed with additives to offset some, mostiy thermal, degradation (32,33). 

The major load-bearing member of cord—mbber composites is the cord, which provides strength and many other critical properties essential for tire performance. Cords in pHes form the stmctural backbone of the tire. The mbber plays the important but secondary role of transmitting load to the cords via shearing stresses at the cord—mbber interface. Other expected performance characteristics of the tire are due to design and manufacturing processes. Table 5 (96) identifies several tire performance characteristics and how they are dependent on tire cord properties. 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Impact and Erosion. Impact involves the rapid appHcation of a substantial load to a relatively small area. Most of the kinetic energy from the impacting object is transformed into strain energy for crack propagation. Impact can produce immediate failure if there is complete penetration of the impacted body or if the impact induces a macrostress in the piece, causing it to deflect and then crack catastrophically. Failure can also occur if erosion reduces the cross section and load-bearing capacity of the component, causes a loss of dimensional tolerance, or causes the loss of a protective coating. Detailed information on impact and erosion is available (49). 

ABS is the sixth largest volume thermoplastic resin and the principal engineering (stmctural or load bearing) plastic (89). ABS is a terpolymer manufactured by copolymerizing acrylonitrile and styrene in the presence of polybutadiene mbber. Important producers of ABS plastics include General Electric, Monsanto (Lustran), and Dow (Abtec) (see Acrylonitrile polymers). 

The purpose of these specifications is to produce a mixture where the fines fill the voids in the coarser fractious, thus to increase load-bearing capacity. (See Refractories above.)... 

---