Hardened state

In general the properties of the adhesive in the hardened state are determined by its internal structure. Strength and elasticity derive 

For the measurement of tensile properties, dumb-bell specimens of the form shown in Fig. 2.13 are suggested. Tensile modulus. Poisson s ratio and elongation at failure may be measured with appropriate strain monitoring equipment and a set of stress/strain curves for a typical range of epoxies is given in Fig. 2.14. Similar 

Specimen thickness = 3 mm Fig, 2.13, Tensile dumb-bell specimen (Ref. 21), 

One way of monitoring the behaviour of a material in shear is with a torsional test. The method has the advantage that, provided a circular specimen is used, a condition of pure shear can be achieved. However, torsion tests can be relatively difficult to perform unless specimens can be machined accurately to avoid warping effects. The alternative is to test a prismatic specimen in a shear box of the form outlined in Fig. 2.15. 

To assess flexural modulus of the hardened adhesive a specimen 200 X 25 X 12 mm deep tested in four point bending may be used. The sample under test is loaded transversely at the third points at a erosshead speed of 1 mm/minute and the eentral deflection recorded (Fig. 2.16). From the load-deflection curve, the secant modulus at 0.2% strain may be calculated. A lower limit on flexural modulus may be specified to prevent problems due to creep of the adhesive under sustained loads, whereas the upper limit will be to reduee stress concentrations arising from strain incompatibilities, for example at ehanges in section. 

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Maximum value for the hardened state given in parentheses. 

During the hardening of PMF-resins no co-condensation occurs in the hardened state two independent interpenetrating networks exist [58]. Indications for a co-condensation via methylene bridges between the phenolic nucleus and the amido group of the melamine had been found by H-NMR only in model reactions between phenolmethylols and melamine. 

The mix proportions for concrete paving mixtures are determined by attaining optimum characteristics of the mix in both the plastic and hardened states. The designed mixture can be properly placed and consolidated, finished to the required texture and smoothness, and will have the desired properties necessary for pavement performance. Concrete paving mixtures should be... 

The initial plastic state of the fresh concrete subsequent to the mixing process, where properties such as the air content, density and workability are normally measured by relevant standard tests, and utilized as a means of control of production. The magnitude of these properties is affected by the addition of water-reducing admixtures, either intentionally or as a side effect, which could result not only in a change in the characteristics in the plastic state, but could also be reflected in changed properties in the hardened state. 

The hardened state at a relatively early date, usually 28 days, when the mechanical properties such as compressive and flexural strength and stiffness are used as a basis of structural design. 

The subsequent hardened state during the life of the structure where the concrete material must fulfill its structural or aesthetic role without deterioration. It is important that the durability of the concrete should not be adversely affected by the presence of a water-reducing admixture. 

The durability of concrete is the ability of the material to maintain its structural integrity, protective capacity, and aesthetic qualities over a prolonged period of time. It is important that the benefits conferred to concrete in the plastic and early hardened state by water-reducing admixtures are not negated by any adverse effect on the long term durability. 

The chemical reaction that takes place during solidification of thermosets also leads to considerable thermal effects. In a hardened state, their thermal data are similar to the ones of amorphous thermoplastics. Figure 2.8 shows the specific heat graphs for the three polymer categories. 

TS melts in the plasticator and cure to a harden state in the mold that operates at a higher temperature than the plasticator (Chapter 1). For the best controlled machines used for molding TSs the heated plasticator usually includes a water jacket to ensure that the melt temperature profile is under control.3... 

Studies of craze microstructure and the surrounding displacements of crazes have established that the only parts around a craze that undergo plastic deformation are concentrated into a process zone at the tip of the craze, and into a fringing layer all around the entire craze body. In the process zone craze matter is generated by one of the two processes discussed above, and fibrils are necked down to the final extension ratio. In the fringing layer, additions are made to craze fibrils by drawing polymer out of half space. Outside the idetifiable parts of a craze, the solid polymer remains entirely elastic while inside the craze body the fully drawn fibers carry the required craze tractions purely elastically in their orientation hardened state at the... 

For passivation treatments other than scale removal following thermal treatment, less aggressive acid solutions are usually employed. The primary purpose of these treatments is to remove contaminants that may be on the component s surface and could prevent the formation of the oxide layer locally. The most common contaminant is imbedded or free iron particle from forming or machining tools. Mechanical polishing can be employed to provide a uniform surface finish and to remove these contaminants. The polishing materials should be used for stainless only as they can carry over small particulates from one part to the next. In addition, the work-hardened state of this fine particulate, even from a stainless vessel, can have a lower threshold for corrosion and act as an initiation site if not removed. A dilute (10%) solution of nitric acid is... 

The impact extrusion process is used to produce open-ended collapsible tubes from softer metals such as tin and lead. When aluminium is used, it work-hardens during the forming process and the resultant tubes must be annealed to regain flexibility. Alternatively aluminium tubes may be left in their work-hardened state as rigid containers. Impact extrusion is a particularly useful process to produce containers with a high length to diameter ratio, e.g. up to 7 1. A slug of the metal to be formed is held in a female die and is struck by a punch which has the same form as that of the inside of the ultimate container. Upon impact the metal flows up the outside of the punch. A stripper plate then removes the extruded container on its return stroke. 

The procedure of mix design should finish with a trial mix (or initial test) in order to check, before the production starts, if the concrete meets all the specified requirements in the fresh and hardened states. 

The basic aim of such experiments is the prediction of the properties of the wood-based panels, hence of the adhesive resin in its hardened state, based on the composition and the properties of the liquid resins used before their hardening. For this purpose various structural components were determined by means of NMR spectroscopy and the ratios of the amounts of the various structural components were calculated, for example ... 

Falling under the heading of metal chelate compounds, the zinc oxide-eugenol (ZOE) cements in the hardened state are essentially zinc phenolates formed by reaction of zinc oxide and eugenol (4-allyl-2-methoxyphenol) in the presence of moisture, embedding... 

Testing program. The properties of the trial mixes in both the fresh and hardened state were determined. Fresh state properties measured were slump and flow parameters and workability when used in conjunction with AR fibre mesh reinforcement. Hardened state properties tested included compressive and flexural strength after 7 days of submersion curing at 26°C. Fresh state properties were measured directly after the mixing was completed. 

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