Warping stresses

Warping stresses develop as a result of the differential temperature (temperature gradient) between the upper and lower surface of the slab. The non-uniform distribution of temperatures within the depth of the concrete slab may cause upward or downward curling. Concrete slab curling has an effect on the pavement s behaviour, which can be attributed to the consequent loss of support (Shi et al. 1993 Tang et al. 1993). 

The problem of warping was addressed by Westergaard (1926) who developed equations for three different cases (with the assumption that the temperature gradient from the top to the bottom of the slab was linear), the simplest of which is given below  

Since then, it has been shown that the temperature gradient is closer to a curve line. This results in calculated stress values that are much lower than those derived by Westergaard (O Flaherty 2002). Work carried out by Zhang et al. (2003) concluded that warping stresses caused by the assumption of linear temperature distribution could be as high as 30% or more. 

For a temperature gradient of 5°C between the top and bottom of a 150 mm slab, the stresses induced by temperature warping are not as detrimental as might be expected (O Flaherty 2002). 

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The design criteria of rigid pavements are far more complicated than those of flexible pavements. The horizontal tensile stresses causing cracking of the slab are generated by the combined effect of wheel loading and thermally induced internal and warping stresses. 

Corner cracking is caused by load repetitions combined with a loss of corner support (subbase or subgrade), poor load transfer across the joint, dowel bar restrain near the edge of the slab and ingress of solids into the joint. The loss of support may be created by pumping or warping stresses. 

Swelled and warped stress 25.1 crack agent Tenite Eastman Specimen 50.8 mm (2 in)X3.2 mm (0.125 in) thick injection molded discs, 0.918 density... 

Ideally, the temperature and relative humidity during drying should be controlled if wood dries too rapidly, it is likely to spHt, check, warp, or honeycomb because of stresses. If wood dries too slowly, it is subject to development of stain and mold growth. 

Rapid cooling can cause residual stresses (leading to accelerated corrosion), distortion and quench cracks. The orientation of the component during processing is important in this respect. Sustained high temperatures can cause warping and softening. 

Warping, residual stresses in pressing, cutting possible surface damage lowered ductility higher DBT. 

The most desirable annealing temperatures for amorphous plastics, certain blends, and block copolymers is just above their glass transition temperature (Tg) where the relaxation of stress and orientation is the most rapid. However, the required temperatures may cause excessive distortion and warping. 

Produce stress-free moldings eliminating product distortion and warping after vulcanization... 

The crimes with which these men are charged were not committed in rage, or under the stress of sudden temptation, What these men did was done with the utmost deliberation and would, I venture to surmise, be repeated if the opportunity should recur. In their. . . supremely criminal adventure, the defendants were eager and leading participants. They joined in stamping out the flame of liberty. They were the warp and woof of the dark mantle of death that settled over Europe. 

Before weaving, the warp is covered with a layer of polymer to withstand the mechanical stress (abrasion, tension) during weaving. These polymer coatings are so-called sizes. Normally native starch, modified starch like carboxymethyl-starch (CMS), carboxymethyl-cellulose (CMC), polyvinylalcohols (PVA), polyacrylates, and proteins can be used. The amount of added polymer for staple yarns like Co is between 8 and 20% of the weight of the warp. As a result, in many cases the final amount of polymer to be removed in the desizing step is approximately 5-10% of the weight of the fabric. 

A related issue has to do with the initial wafer-level uniformity (wafer thickness, wafer warp and bow, thicknesses of thin films across the wafer surface, uniformity of stress in such thin films across the wafer) and the subsequent impact on wafer-level polish performance. Some examination has been made of the impact of wafer warp and bow on the polish performance [68], where it was found that the initial warpage can have significant impact (with the implication that reclaimed wafers may not be appropriate monitors of wafer-level polish performance). Other work has considered inherent variation due to Von Mises stress concentrations at the edge of the wafer (conceptually, a downward pressure on the wafer causes lateral stress buildup near the edge of the wafer) [64]. 

In addition to the occurrence of the residual stress, cells warp toward the cathode side because of the mismatch of the thermal expansion behavior between the electrolyte and anode. Thus, the deformations of cells at room temperature are also... 

The as-grown cells are usually extremely warped toward the cathode side at room temperature. To reduce the warp, the cells are flattened at 1400°C with a distributed load on the surface. The flattening treatment could reduce the warp at room temperature indicating that the sample is in a plastic state at 1400°C. In contrast, it was reported that the sintering of YSZ does not proceed well below 1250°C [25], Thus, it is considered that the temperature at which both the electrolyte and anode are constrained is between 1250°C to 1400°C. When the temperature at which the electrolyte and anode are constrained is assumed to 1400°C, the calculated residual stress is close to the measured value. 

A major challenge is the densification of the graded powder compacts. The processing of FGM materials by powder metallurgy methods often faced undesirable excessive bending or warping of the component after sintering (Miyamoto et al., 1999). Due to excessive thermal residual stresses, cracks and other defects may often be observed in the final FGM component unless properly manufactured. 

As wetting and drying occur, boards may warp. The wood loses its surface coherence, becomes friable, and splinters and fragments come off. Of the elements contributing to the weathering process, UV irradiation from the sun and stresses imposed by wetting and drying are the most important in the majority of climates. 

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