Exposure to Condensation Moisture of Sheathing in Retrofitted Leaky Wall Assemblies

Exfiltration of moist indoor air during winter conditions may lead to the gradual wetting of the sheathing of wall assemblies that are not airtight. In this study, seven full-scale wood-frame wall specimens were tested to evaluate the impact of both the geometry of the air leakage path and the addition of rigid insulation on the warm side or the cold side of the assembly on the hygrothermal response of wall assemblies. Walls were exposed to 72?days of steady-state winter conditions and 47?days of steady-state late spring conditions. The position of the added rigid insulation and the geometry of the air leakage paths were different in each wall specimen. The moisture content of the fiberboard sheathing was monitored, and the results are presented. The evolution over time of the moisture distribution across the plane of the sheathing is also presented. The duration of exposure to moisture content above 19 and 28% is examined, allowing a comparison of the performance of the specimens. Leaky assemblies with vapor-tight insulation board added on their cold side were exposed to high moisture content longer than the assemblies not reinsulated or reinsulated on their warm side because the assemblies without insulation on the cold side of the sheathing were exposed to a buildup of frost that prevented moisture to be absorbed by the sheathing.     

Microstructure and strength of nanocrystalline copper alloy prepared by mechanical alloying

Polycrystalline materials having an ultrafine grain size may be prepared by mechanical alloying. Such a material has been prepared here with a copper matrix and a uniform dispersion of particles which stabilises the fine microstructure. It is shown that the grain size of the copper matrix may be explained in terms of the conventional models of boundary pinning by particles, even for grain sizes below 40 nm. For grain sizes larger than about 100 nm, material strength may be explained by dislocation-particle interactions as illustrated by TEM observations. For grain sizes below this limit, however, strengthening is not as great as dislocation theory would predict based on the distribution of particles in the material; in addition TEM observations show no indication of the presence of dislocations. A different deformation mechanism seems to control strengthening for these materials of nano-scale grain size.     

含Nb-Ti微合金钢第三脆性区铸坯缺陷

采用金相显微镜、复型萃取、SEM、TEM对析出物的形貌、尺寸、数量进行统计分析,并利用Gleeble-1500热模拟试验机,系统研究了含Nb-Ti微合金钢第三脆性区的热塑性。结果表明:温度在950~700℃范围内时,断面收缩率最小为25.7%。析出物以TiN、Nb(CN)为主,950℃时粒子尺寸在50nm左右。随着温度的降低,粒子数量密度由51个/μm2增加到580个/μm2,尺寸随之减小。975℃的抗拉强度及临界应力分别为58.3、61.0 MPa。975℃以上,临界应力小于抗拉强度,不易发生沿晶断裂。975℃以下时,晶粒变形临界应力大于抗拉强度,产生沿晶断裂。     

含尖晶石空心球的刚玉-尖晶石材料制备及性能

采用电熔-喷吹法制备了镁铝尖晶石空心球,结合空心球结构与性质特征,将其引入刚玉-尖晶石材料,对比研究了不同粒径空心球对材料显微结构、力学强度及隔热能力的影响.结果 表明:制备的空心球球形度高,球壁由单层或多层镁铝尖晶石晶粒镶嵌结合而成,球体的抗压能力取决于球壁厚度及其均匀性.降低粒径、引入复合粒径空心球,通过球体之间的...     

Elevated temperature compressive properties of N-doned NiAl

The elevated temperature properties of NiAl slightly enriched with ~900 appm nitrogen by atomizing the aluminide to powder under a nitrogen atmosphere have been determined. Compression samples were machined from hot extruded material and tested in air between 1100 and 1400 K under both constant velocity and constant load conditions. It appears that N in solid solution contributes little to the creep strength of B2 nickel aluminide. Excess nitrogen leading to the formation of A1N and A1(O,N) particles, however, can have a pronounced effect on creep behavior. These fine secondphase particles stabilize a small grain structure which, in turn, can improve or reduce the mechanical strength, depending on the deformation conditions. Under certain test conditions, high-angle grain boundaries can break away from the particles and overall grain growth occurs, leaving behind a network of A1N and A1(O,N) particles. This network of particles is very effective in anchoring a small, stable subgrain structure that provides elevated temperature strength without being subject to undesirable, weakening grain-boundary deformation mechanisms. Overall, the results provide further evidence that creep in NiAl is dislocation-climb controlled which involves subgrain formation and that stabilization of subgrains will improve mechanical strength in the manner proposed by Sherbyet al.     

Influence of cold work and recovery on the strength and toughness of iron

In this work some of the structures typical of those found in thermomechanically processed steels were reproduced by cold work, cold work and recovery, and recrystallization treatments of vacuum-melted iron single-crystals and polycrystals. The mechanical properties of the microstructural features such as subgrain formation, texture development, and grain elongation were recorded. It was shown that although the dislocation subboundaries produced on recovery add an increment of strength to that produced by grain boundaries, they are less effective strengtheners than high-angle grain boundaries. Further, the data suggests that yield strength is related not only to subgrain size but also to the angle of misfit of the subgrain boundaries. Although strength increased with subgrain boundary formation, toughness remained constant. Consequently, the introduction of subgrain boundaries offers a means of improving strength while maintaining toughness. The ductile-to-brittle transition temperature of cold-worked as well as cold-worked and recovered polycrystalline iron varied with specimen orientation relative to the direction of deformation. These variations were primarily a function of the anisotropy of grain dimension that is produced by cold deformation. Toughness was not influenced by the preferred orientations produced by the various processing techniques.     

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Two powder metallurgy nickel-base turbine disk alloys, RENE’95* and KM4, were studied for strength and deformation behavior at 650 °C. Two classes of microstructures were investigated: unimodal size distributions of γ′ precipitates with particle sizes ranging from 0.1 to 0.7 μm and commercially heat-treated structures with bimodal or trimodal size distributions of γ′ precipitates. The strength and deformation mechanisms were heavily influenced by the microstructure. In both alloys, deformation during compression tests consisted of a combination of a/2〈110〉 antiphase boundary (APB)-connected dislocation pairs and a/3〈112〉 partials creating superlattice intrinsic stacking faults (SISFs). In unimodal alloys, the fault density increased with decreasing particle size and decreasing strain rate. These trends, observed in compression testing, are consistent with earlier studies of similar alloys, which were tested in creep. As the γ′ size was reduced, the nature of the faults changed from being isolated within single precipitates to being extended across entire grains. Commercially heat-treated alloys, containing a bimodal distribution of γ′ particles, exhibited significantly more faulting than unimodal alloys at the same cooling γ′ size. This augmentation of the faulting in commercial alloys was apparently due to the presence of the fine, aging γ′ particles. The two typical commercial heat treatments (supersolvus and subsolvus) resulted in different deformation structures: the subsolvus behavior was similar to that of unimodal alloys with γ′ sizes between 0.2 and 0.35 μm, while the supersolvus deformation was similar to that of unimodal alloys with the 0.1 μm γ′ size. These differences were attributed to differences in the size of the fine, aging γ′ particles. Creep deformation in a commercially heat-treated material at 650 °C occurred solely by SISF-related mechanisms, resulting in a macroscopic slip vector of 〈112〉. The effects of alloy chemistry, APB energy, and microstructure on the deformation and mechanical behavior are discussed in detail, and possible effects of the faulting mechanisms on the mechanical behavior are explored. Finally, models for yield strength as a function of microstructure for bimodal alloys with large volume fractions of precipitates are found to be in need of development. RENE′95 is a trademark of General Electric Company, Fairfield, CT.     

Subassembly generation via mechanical conformational switches

A question is posed on how a particular subassembly sequence is generated in randomized assembly. An extended design of mechanical conformational switches [16] is proposed that can encode several subassembly sequences. A particular subassembly sequence is generated due to conformational changes of parts during one-dimensional randomized assembly. The optimal subassembly sequence that maximizes the yield of a desired assembly can be found via genetic search over a space of parameterized conformational switch designs, rather than a space of subassembly sequences. The resulting switch design encodes the optimal subassembly sequence so that the desired assemblies are put together only in the optimal sequence. The results of genetic search and rate equation analyses reveal that the optimal subassembly sequence depends on the initial concentration of parts and the defect probabilities during randomized assembly. The results indicate that abundant parts and parts with high defect probabilities should be assembled earlier rather than later.     

Ce在钼合金中的存在形态及其对力学性能的影响

实验研究了稀土元素Ce在钼丝制备过程中的存在形态以及对其性能的影响。结果表明,在通过MoO2粉末和Ce(NO3)3溶液的固-液掺杂、还原获得的Mo-Ce合金粉末中,Ce元素以CeO2形态存在;在烧结坯中,较大尺寸的CeO2质点分布于晶界,较小尺寸的CeO2质点分布于晶内;在丝材成形过程中,晶内CeO2质点逐渐变形为纤维状,晶界CeO2质点仍呈球状,未发生变形。CeO2的存在不但细化了钼粉,同时弥散分布在烧结坯基体中,起到了一定的韧化作用。对不同Ce含量的Mo-Ce合金而言,CeO2存在形式有所不同,导致其塑性有所差异。     

Microstructural Examination of a Grade 100 Microalloyed Steel and Correlation with Yield Strength

Abstract

The microstructure of a Grade 100 microalloyed steel was examined in terms of the iron matrix phases and microalloy precipitates using electron microscopy. Since microalloyed pipeline and structural steels are currently graded according to their yield strength, the different microstructural factors that affect the yield strength of the steel were assessed and their contributions to the strength were estimated. The microstructural factors include grain size, precipitate size and volume fraction, solid solution content and dislocation density. Accurate grain size measurements were only possible through high resolution electron microscopy imaging that made it possible to resolve grain/sub-grain boundaries of micron and sub-micron sized grains/subgrains. It was found that the increased strength was mainly due to the formation of bainitic structures with fine grain/sub-grain sizes. The contribution from other strengthening sources such as precipitates, dislocations and atoms in solid solution was significantly less.     

Hydroxyapatite-polyethylene composites for bone substitution: effects of ceramic particle size and morphology

Synthetic hydroxyapatite particles of two median sizes and different morphologies have been used to manufacture hydroxyapatite reinforced high density polyethylene composites (HAPEX) for medical applications. The effects of hydroxyapatite particle size on properties of the resultant composites were investigated using various techniques. It was found that composites with smaller hydroxyapatite particles had higher torsional modulus, tensile modulus and tensile strength, but lower strain to failure. Examination of fracture surfaces revealed that only a mechanical bond existed between the filler and the matrix. It was shown that dynamic mechanical analysis is useful in studying the viscoelastic behaviour of the composite.     

On the Phenomenon of Stress Drop During Hot Deformation of ZrTiAlV Alloy

Hot deformation behaviors of 47Zr-45Ti-5Al-3V alloys with different grain sizes were investigated by compression tests. The flow curves exhibited a pronounced stress drop at the very beginning of deformation. The magnitude of the stress drop increased with the decreasing deformation temperature and the increasing strain rate. The sudden stress drop may be associated with the disappearance of mobile dislocations in the grain boundaries. Larger initial grain size increased the flow stress, promoted the stress drop, and enhanced the activation energy of deformation.     

Metallographic Aspects of Deformation and Fracture of Hard Alloys under Compression

We have studied the mechanism of plastic deformation and fracture of tungsten-cobalt hard alloys over a broad range of compositions and grain sizes of the carbide phase in different stages of loading by uniaxial compression. We have shown that the behavior of each phase component is due to the cobalt content in the alloy and the tungsten carbide grain size. When the alloys are loaded to the yield stress, microcracks appear in them which are stopped at this stage by the deformed layers of the alloy. Residual strain of the hard alloys under uniaxial compression is the result of at least three deformation processes occurring in the alloys when they are loaded: slip along interphase and intergrain boundaries with the appearance of microcracks at this sites, slip in WC grains, and deformation of the cobalt phase. We conclude that slip in the cobalt phase is one of the basic mechanisms for its deformation when the alloys are loaded by compression.     

Effect of the lamellar grain size on plastic flow behavior and microstructure evolution during hot working of a gamma titanium aluminide alloy

The kinetics of dynamic spheroidization of the lamellar microstructure and the associated flow-softening behavior during isothermal, constant-strain-rate deformation of a gamma titanium aluminide alloy were investigated, with special emphasis on the role of the prior-alpha grain/colony size. For this purpose, fully lamellar microstructures with prior-alpha grain sizes between 80 and 900 μm were developed in a Ti-45.5Al-2Nb-2Cr alloy using a special forging and heat-treatment schedule. Isothermal hot compression tests were conducted at 1093 °C and strain rates of 0.001, 0.1, and 1.0 s⁻¹ on specimens with different grain sizes. The flow curves from these tests showed a very strong dependence of peak flow stress and flow-softening rate on grain size; both parameters increased with alpha grain/colony size. Microstructures of the upset test specimens revealed the presence of fine, equiaxed grains of γ + α ₂ + β phases resulting from the dynamic spheroidization process that initiated at and proceeded inward from the prior-alpha grain/colony boundaries. The grain interiors displayed evidence of microkinking of the lamellae. The frequency and severity of kinking increased with strain, but were also strongly dependent on the local orientation of lamellae with respect to the compression axis. The kinetics of dynamic spheroidization were found to increase as the strain rate decreased for a given alpha grain size and to decrease with increasing alpha grain size at a given strain rate. The breakdown of the lamellar structure during hot deformation occurred through a combination of events, including shear localization along grain/colony boundaries, microbuckling of the lamellae, and the formation of equiaxed particles of γ + β ₂ + α ₂ on grain/colony boundaries and in zones of localized high deformation within the microbuckled regions.     

钒在低温大变形条件下对晶粒细化的影响

研究了不同钒含量的低碳钢在大变形条件下轧制时的力学性能和铁素体晶粒尺寸,结果表明：轧制温度较高时,钒对晶粒细化没有影响,而轧制温度较低时,低碳钢中加入钒可以细化铁素体晶粒,提高材料的屈服强度和抗拉强度。     

Calcium phosphates in pharmaceutical tableting. 2. Comparison of tableting properties

Ten calcium phosphates suitable for direct compression (dibasic calcium phosphate dihydrate, dibasic calcium phosphate anhydrous and hydroxylapatite) were investigated with respect to their compressional behaviour. Except for Di-Cafos A all products gave tablets with sufficient to good mechanical strength. Nevertheless, there were differences between the products. All tablets prepared from the different products showed a high friability. This seems to be a problem of the calcium phosphates in general. On the other hand, the influence of magnesium stearate on the mechanical strength of the tablets was negligible for all products investigated. Moreover, a considerable effect of the particle size on the tensile strength of the tablets was found. The ejection forces and residual pressures were high in general, but critical only in the case of hydroxylapatites. Heckel plots were used to differentiate between plastic deformation and brittle fracture of the particles. In the case of calcium phosphates the slope of the Heckel plots indicated the hardness of the particles rather than their deformation behaviour.     

Microstructural characterization of warm-worked commercially pure aluminum

The deformation microstructures of commercially pure aluminum deformed by plane strain compression to 50 pct thickenss reduction at temperatures between 100 °C and 300 °C, under two strain rates, 5×10⁻² s⁻¹ and 5×10⁻⁴ s⁻¹, have been characterized by transmission electron microscopy. As the deformation temperature increases, the deformation microstructure gradually changes from a checkerboard pattern into an equiaxed subgrain structure with increasing subgrain size. The fraction of geometrically necessary boundaries (GNBs) found in warm-worked aluminum is much less than that found at room temperature. The average misorientation of dislocation boundaries appears to be independent of deformation temperature and strain rate. The constancy of the average misorientations is a combined effect of the variation of the fractions of GNBs and incidental dislocation boundaries (IDBs) and the variation of the average misorientations of GNBs and IDBs. Scaling theory can apply to both boundary misorientations and subgrain sizes that formed at different temperatures and strain rates. Subgrain size distributions for different temperatures and strain rates all resemble a lognormal distribution.     

Microstructural characterization of warm-worked commercially pure aluminum

The deformation microstructures of commercially pure aluminum deformed by plane strain compression to 50 pct thickness reduction at temperatures between 100 °C and 300 °C, under two strain rates, 5 × 10⁻² s⁻¹ and 5 × 10⁻⁴ s⁻¹, have been characterized by transmission electron microscopy. As the deformation temperature increases, the deformation microstructure gradually changes from a checkerboard pattern into an equiaxed subgrain structure with increasing subgrain size. The fraction of geometrically necessary boundaries (GNBs) found in warm-worked aluminum is much less than that found at room temperature. The average misorientation of dislocation boundaries appears to be independent of deformation temperature and strain rate. The constancy of the average misorientations is a combined effect of the variation of the fractions of GNBs and incidental dislocation boundaries (IDBs) and the variation of the average misorientations of GNBs and IDBs. Scaling theory can apply to both boundary misorientations and subgrain sizes that formed at different temperatures and strain rates. Subgrain size distributions for different temperatures and strain rates all resemble a lognormal distribution.     

Microstructural characterization of warm-worked commercially pure aluminum

The deformation microstructures of commercially pure aluminum deformed by plane strain compression to 50 pct thickenss reduction at temperatures between 100 °C and 300 °C, under two strain rates, 5×10⁻² s⁻¹ and 5×10⁻⁴ s⁻¹, have been characterized by transmission electron microscopy. As the deformation temperature increases, the deformation microstructure gradually changes from a checkerboard pattern into an equiaxed subgrain structure with increasing subgrain size. The fraction of geometrically necessary boundaries (GNBs) found in warm-worked aluminum is much less than that found at room temperature. The average misorientation of dislocation boundaries appears to be independent of deformation temperature and strain rate. The constancy of the average misorientations is a combined effect of the variation of the fractions of GNBs and incidental dislocation boundaries (IDBs) and the variation of the average misorientations of GNBs and IDBs. Scaling theory can apply to both boundary misorientations and subgrain sizes that formed at different temperatures and strain rates. Subgrain size distributions for different temperatures and strain rates all resemble a lognormal distribution.     

The effect of grain boundary orientation on creep and rupture of IN-738 and nichrome

Creep rupture specimens taken from directionally solidified ingots of IN-738 and Nichrome in which the grain boundaries were oriented longitudinally, transversely, and 45 deg to the stress axis have been tested over a range of temperature and stress. For both alloys, the ductility was appreciably higher in the longitudinal orientation; but in IN-738, the creep strength was higher in the other two orientations. The net effect on rupture life was small for the superalloy. The nichrome showed much greater scatter which was due partly to inhomogeneous deformation and local recrystallization at the higher temperatures. Because of the recrystallization, even the longitudinal specimens showed intergranular failure for nichrome. The microstructural features of intergranular cracking both internally and on the surface are documented. It is suggested that surface cracking may be an important contributory factor in leading to reduced life with decreased section size which is commonly observed in conventionally cast superalloys.