Corner Deformation

Injection molded parts with comers (i.e., the local L or C geometry) often show inward comer warpage (Ammar et al. 2003 Bakharev et al. 2005). This phenomenon is believed to be caused by the following two effects  

The first is the asymmetric cooling effect In the comer region, heat transfer during cooling is slower inside the comer than outside. Thus, as has been discussed by Boitout et al. (1995), in the case that the gate freezes before the total thickness is totally solidified, the comer will warp toward the hotter side. 

As the resulting angle deformation is independent of the radius r, the same result can be obtained for sharp comer (r 0) as well. Equation 6.63 indicates that the change in the comer angle (the internal comer angle is 7r — 0) is due to the 

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In the soldedess wrap (Fig. 3) or wire-wrap connection, a wire conductor is coiled around the back end of the separable contact, which has a square or rectangular cross section (4). The corners of the soldedess wrap post and the areas of the wire that are in contact with it are severely deformed. In a propedy made wrap, the force required to sHde the wire along the post exceeds the breaking strength of the wire. The method is suitable only for soHd wire, and special tools are used to make this connection. 

Fig. 21a-d. Flow from startup into a 4 1 contraction computed for the pom-pom model with fixed total and cross-bar molecular weight and Weissenberg number (dimensionless deformation rate) of 3[(a) and (b)] and 8 [(c) and (d)]. (a) and (c) show (colour coded) the level of dimensionless stretch of the pom-pom cross-bar, X. (b) and (c) show the respective streamlines. Note the spur of preoriented material joining the wall to the funnel and the reduction of the corner vortex at high flow rates when extension thinning sets in. (Computations courtesy of Dr. T. M. Nicholson)... 

Bubbles and drops tend to deform when subject to external fluid fields until normal and shear stresses balance at the fluid-fluid interface. When compared with the infinite number of shapes possible for solid particles, fluid particles at steady state are severely limited in the number of possibilities since such features as sharp corners or protuberances are precluded by the interfacial force balance. 

Nerve - The elastic resistance of raw rubber or compounds to permanent deformation during processing. A nervy tank lining will be difficult to lay around tight bends or in corners because of springback. 

Palmquist (1957) was the first to make use of the deformation developing around the Vickers pyramid indentation as an aid in the interpretation of results. The Palmquist test consists of determining the resistance of brittle materials to propagation of the cracks appearing at the corners of the Vickers pyramid mapping on a polished surface. The measured value, defined as Palmquist toughness, is given by the formula... 

The basic design needs to be confirmed by the customer. Does the proposed part actually look like what is required, and will it fit into the rest of the equipment if it is part of a larger assembly If not previously discussed with the supplier, any potential trouble points like sharp corners or butt joints should be brought to the attention of the customer and the potential problems resolved. If the part is a noncritical item or if there is knowledge available from previous similar items, the part can be evaluated by the customer. Flexibility, deformation under load, and correct functioning in an assembly can be verified using the part. 

The deformation of crystal seems to be more enhanced in the corner-cut crystal than in the cubic one within the same dissolution period. 

With regard to the ion-water interactions, one can see that the water molecules exert a small force on the cations toward the liquid (KF), or practically no force (CsF, KC1), but in the most cases (NaF, LiCl, NaCl) a force toward the crystal. In all cases no cation has dissolved within the time examined. On the other hand, water molecules exert a force on the anions toward the liquid in all cases. If the force is large (CsF, LiCl, NaCl) the anions dissolve if it is small (KF, KC1) the anions do not dissolve. An exception is NaF, where the force acting on fluoride at a corner is large but no fluoride dissolves. In this case, however, the crystal structure of the NaF deforms quite remarkably, and the whole crystal seems to be in a semidissolved state (Fig. 4a). 

Fig, 19. (a) Sketch of the channel-die apparatus used for the deformation experiment. Dimensions are in millimetres. The compression stamp is moved along the deformation direction D. The flow of the sample is constrained by the rigid walls of the die in the direction C, and free flow is possible in the direction F. (b) Stress (cr)-strain(e) diagram resulting from channel-die extrusion of bisphenol-A polycarbonate at 300 K and a strain rate of e = 0.01 s l. (c, d) Dipolar DECODER spectra of 13C-labelled bisphenol-A polycarbonate before and after deformation. The spectra exhibit a characteristic star-like ridge pattern. Each of three types of corners (C, D, F) in the pattern corresponds to vectors oriented along a particular direction in the channel-die used for the experiment, (e, f) The anisotropy caused by the deformation becomes readily visible in the difference spectrum (deformed minus undeformed). For clarity, the negative (f) and positive contours (e) have been drawn separately. (Reproduced from Utz et al. with permission.)... 

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