Differential Shrinkage Research Articles

Influence of mineral additions and different compositional parameters on the shrinkage of structural expanded clay lightweight concrete

A comprehensive experimental study was carried out on the shrinkage behaviour of structural expanded clay lightweight aggregate concrete (LWC), taking into account different compositions, types and initial wetting conditions of lightweight aggregates (LWA). The influence of different compositional parameters on shrinkage, such as the type and volume of aggregate, the w/c ratio, the binder content and the partial replacement of normal aggregates by LWA was analysed. The shrinkage of LWC depends on how the volume of LWA varies. The influence of different pozzolanic materials was also studied, namely, silica fume, nanosilica and fly ash. Depending on the type, content and reactivity of the pozzolanic additions, the shrinkage was higher or lower than that of LWC without admixtures. The initial wetting condition of LWA had little influence on the long-term shrinkage. The LWC with the most porous aggregates is more affected by the cross-section geometry of concrete in that it is more susceptible to differential shrinkage. Current standard expressions did not properly predict the shrinkage behaviour of LWC. Multiplier coefficients of about 1.3 for the most common structural LWA and about 1.6 for more porous LWA are suggested, to take into account the higher long-term shrinkage of LWC.

Warpage Analysis with Straight Drilled and Conformal Cooling Channels on Front Panel Housing by Using Taguchi Method

The challenging in injection molding process is to get the uniform thermal distribution on the molded parts during the cooling stage which is mainly depend on the design of the cooling channels in injection mold. Poor design of cooling channels will result a non-uniform thermal distribution which lead to a longer cycle time, differential shrinkage and warpage defects on the molded parts. In this study, the performance of conformal cooling channels compared to the straight drilled cooling channels in order to minimize the warpage on the front panel housing is evaluated. The simulation results from Autodesk Moldflow Insight (AMI) 2013 are analyzed by using Taguchi Method and Analysis of Variance (ANOVA). The analyses show that conformal cooling channels are able to improve the quality of the molded parts in term of warpage compared to the conventional straight drilled cooling channels and the results are beneficial for the molding industries which involving the precise parts.

Research on Automatic Safety Monitoring System for Artificial Islands

To meet the needs of the security for the oil and gas production, the safety monitoring methods and technical requirements for the artificial islands in coastal areas during the operation periods are presented. This thesis constructs on the basis of safety monitoring during artificial island operation periods in Jidong Nanpu ilfield, which develops and establishes automatic safety monitoring system of artificial island in China for the first time. The result of preliminary operating shows that the artificial island 1-3# exhibits obvious differential settlement and shrinkage phenomenon during the operation periods. The research results provide ten technical basis and guarantees for the safety construction and management of artificial islands .It will play a guiding role in the safety monitoring during the operation periods.

Warpage Analysis between Straight and Conformal Cooling Channels on Thin Shallow Shell

Warpage is a type mold defect due to non-uniform temperature variation which causes differential shrinkage rate on the moulded parts. An accurate warpage prediction is so important in helping mould designers to achieve successful mold design with minimum warpage defects. This work is performed with a purpose to determine and compare the best parameters can be selected in manufacturing of thin shallow shell using two different types of cooling channels which are straight cooling channels and conformal cooling channels. The results were obtained using Taguchi Method and Analysis of Variance (ANOVA) and run through simulation software. Both parameters are then compared with each other in recommending to the mold designers which is the best to be applied at mold design stage. It has been found from this work that two factors that significantly cause warpage on both cooling channels are packing pressure and filling time.

Improved method of producing satisfactory sections of whole eyeball by routine histology

To overcome the loss of structural integrity when eyeball sections are prepared by wax embedding, we experimentally modified the routine histological procedure and report satisfactorily well-preserved antero-posterior sections of whole eyeballs for teaching/learning purposes. Presently histological sections of whole eyeballs are not readily available because substantial structural distortions attributable to variable consistency of tissue components (and their undesired differential shrinkage) result from routine processing. Notably, at the dehydration stage of processing, the soft, gel-like vitreous humor considerably shrinks relative to the tough fibrous sclera causing collapse of the ocular globe. Additionally, the combined effects of fixation, dehydration, and embedding at 60°C renders the eye lens too hard for microtome slicing at thicknesses suitable for light microscopy. We satisfactorily preserved intact antero-posterior sections of eyeballs via routine paraffin wax processing procedure entailing two main modifications; (i) careful needle aspiration of vitreous humor and replacement with molten wax prior to wax infiltration; (ii) softening of lens in trimmed wax block by placing a drop of concentrated liquid phenol on it for 3 h during microtomy. These variations of the routine histological method produced intact whole eyeball sections with retinal detachment as the only structural distortion. Intact sections of the eyeball obtained compares well with the laborious, expensive, and 8-week long celloidin method. Our method has wider potential usability than costly freeze drying method which requires special skills and equipment (cryotome) and does not produce whole eyeball sections.

Side Weld and Bend Method of Manufacturing Compliant Plate Seals

Compliant plate seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines, and oil and gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inward from the seal outer diameter and an intermediate plate extends inward into this slot from the stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip clearance. Due to this self-correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and robust noncontact operation even in the presence of large rotor transients. Manufacturing of compliant plate seals is a challenging problem and in this paper we describe the development of a novel manufacturing technique called side weld and bend (SWAB). The compliant plates are tightly packed with alternating spacer shims in a straight line fixture and welded to a top plate from the side along a straight line. After removal of the spacer shims, the welded assembly is bent to form an arcuate seal of a desired diameter. The side weld and bend (SWAB) manufacturing method reduces distortion, deformity, differential shrinkage, and other associated problems with welding across gaps between adjacent compliant plate seals as is typical in current manufacturing processes.

Distortion in a 7xxx Aluminum Alloy during Liquid Phase Sintering

The distortion in a sintered 7xxx aluminum alloy, Al-7Zn-2.5Mg-1Cu (wt. pct), has been investigated by sintering three rectangular bars in each batch at 893 K (620 °C) for 0 to 40 minutes in nitrogen, followed by air or furnace cooling. They were placed parallel to each other, equally spaced apart at 2 mm, with their long axes being perpendicular to the incoming nitrogen flow. Pore evolution in each sample during isothermal sintering was examined metallographically. The compositional changes across sample mid-cross section and surface layers were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy depth profiling, respectively. The two outer samples bent toward the middle one, while the middle sample was essentially distortion free after sintering. The distortion in the outer samples was a result of differential shrinkage between their outer and inner surfaces during isothermal sintering. The porous outer surface showed an enrichment of oxygen around the large pores as well as lower magnesium and zinc contents than the interior and inner surface of the same sample, while the inner surface was distinguished by the presence of AlN. The differential shrinkage was caused by different oxygen contents in local sintering atmosphere and unbalanced loss of magnesium and zinc between the outer and inner surfaces.

A Novel Approach to the Preparation of a Highly Crystallized BaTiO3 Layer on Ni Nanoparticles

A novel chemical approach is proposed to facilitate the crystallization of the BaTiO3 coating layer on Ni nanoparticles for multilayer ceramic capacitors. Based on the chemical equilibrium principle, the polycrystalline coating layer can be obtained at atmospheric pressure and at a relatively low temperature by a one‐step reaction. The details of the coating process of the Ni nanoparticles are clearly discussed. The coating is uniform, dense, and well crystallized, and can protect the Ni from oxidation and also shift the starting point of Ni densification to a higher temperature, reducing differential shrinkage issues in the co‐firing.

Shrinkage cracking in Roman cement pastes and mortars

Roman cements were key materials used in the architecture of the nineteenth and early twentieth centuries. Fine cracks, caused by restrained shrinkage during drying, are a distinct characteristic of all Roman cement stuccoes. Today, cracking has become an important barrier preventing broader acceptance of Roman cement as a material by the restoration and construction sector. Drying shrinkage and tensile properties of Roman cement pastes and mortars submitted to various curing and drying regimes were determined as key parameters controlling cracking. A higher volume of aggregate in the mortar mix and a moderate curing time produce optimum Roman cement mortars from the standpoint of reducing the risk of cracking. Fast drying produced significant microcracking due to moisture gradients and differential shrinkage across the specimens. Stress relaxation observed during the long-time loading of the materials reduced their vulnerability to cracking.

Prediction of Complex Human Traits Using the Genomic Best Linear Unbiased Predictor

Despite important advances from Genome Wide Association Studies (GWAS), for most complex human traits and diseases, a sizable proportion of genetic variance remains unexplained and prediction accuracy (PA) is usually low. Evidence suggests that PA can be improved using Whole-Genome Regression (WGR) models where phenotypes are regressed on hundreds of thousands of variants simultaneously. The Genomic Best Linear Unbiased Prediction (G-BLUP, a ridge-regression type method) is a commonly used WGR method and has shown good predictive performance when applied to plant and animal breeding populations. However, breeding and human populations differ greatly in a number of factors that can affect the predictive performance of G-BLUP. Using theory, simulations, and real data analysis, we study the performance of G-BLUP when applied to data from related and unrelated human subjects. Under perfect linkage disequilibrium (LD) between markers and QTL, the prediction R-squared (R2) of G-BLUP reaches trait-heritability, asymptotically. However, under imperfect LD between markers and QTL, prediction R2 based on G-BLUP has a much lower upper bound. We show that the minimum decrease in prediction accuracy caused by imperfect LD between markers and QTL is given by (1−b)2, where b is the regression of marker-derived genomic relationships on those realized at causal loci. For pairs of related individuals, due to within-family disequilibrium, the patterns of realized genomic similarity are similar across the genome; therefore b is close to one inducing small decrease in R2. However, with distantly related individuals b reaches very low values imposing a very low upper bound on prediction R2. Our simulations suggest that for the analysis of data from unrelated individuals, the asymptotic upper bound on R2 may be of the order of 20% of the trait heritability. We show how PA can be enhanced with use of variable selection or differential shrinkage of estimates of marker effects.

Differential brain shrinkage over 6 months shows limited association with cognitive practice

The brain shrinks with age, but the timing of this process and the extent of its malleability are unclear. We measured changes in regional brain volumes in younger (age 20–31) and older (age 65–80) adults twice over a 6months period, and examined the association between changes in volume, history of hypertension, and cognitive training. Between two MRI scans, 49 participants underwent intensive practice in three cognitive domains for 100 consecutive days, whereas 23 control group members performed no laboratory cognitive tasks. Regional volumes of seven brain structures were measured manually and adjusted for intracranial volume. We observed significant mean shrinkage in the lateral prefrontal cortex, the hippocampus, the caudate nucleus, and the cerebellum, but no reliable mean change of the prefrontal white matter, orbital-frontal cortex, and the primary visual cortex. Individual differences in change were reliable in all regions. History of hypertension was associated with greater cerebellar shrinkage. The cerebellum was the only region in which significantly reduced shrinkage was apparent in the experimental group after completion of cognitive training. Thus, in healthy adults, differential brain shrinkage can be observed in a narrow time window, vascular risk may aggravate it, and intensive cognitive activity may have a limited effect on it.

Numerical and experimental study of moisture-induced stress and strain field developments in timber logs

When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.

Investigation into the failure of Inconel exhaust collector produced by laser consolidation

Among layer manufacturing techniques, Laser Consolidation (LC) finds its ideal application in the production of thin-walled metal parts for industrial niches characterised by high innovation and product complexity. To fully exploit the technological potential, developments must be made to assess LC’s repeatability and reliability. Previous studies proved that high strength parts of fine microstructure are obtained if appropriate build strategies are used. The aim of this research is to analyse a racecar exhaust collector, built in Inconel by LC, relating the failure modes and microstructure to the construction plan.The exhaust collector component was built using a custom strategy and was run on a dynamometer before failing after approximately 1200km. An investigation of the failure mechanism was carried out by a primary macroscopic analysis, aided by an X-ray control and dye penetrant test. Metallographic sections were then sampled from the critical areas to study the microstructure and relate it to the manufacturing process.Results proved that the distribution of primary microcracks associated with internal residual stresses caused by the build strategy and aggravated by differential shrinkage during the test thermocycles was responsible for ultimate failure. This issue was a result of build strategy and the non-coaxial laser head, therefore, alternative pathways could be developed capable of removing most, if not all, of the contributory factors. The analysed case suggests that LC build strategy selection is as critical to ensure low cycle fatigue resistance as component design and confirms that LC is effective in the production of advanced technological parts with high geometrical complexity given the correct build strategy.

Sensitivity analysis of parameters affecting the drying behaviour of durum wheat pasta

In this work, a comprehensive model of pasta drying combining Neumann boundary conditions, differential shrinkage and with consideration of the constant drying rate period and falling drying rate period was investigated through sensitivity and uncertainty analysis. Results confirmed that shrinkage, moisture loss and drying rate during the constant drying rate period and external resistance to mass transfer did not have a significant impact on the predicted required drying time. The predicted required drying time was influenced predominantly by the effective moisture diffusion coefficient. A correlation to estimate the effective moisture diffusion coefficient was developed from published values and was used to predict the required drying time with an uncertainty of ±3.5h at a 90% confidence interval. Since this magnitude of uncertainty is unreasonable for most industrial uses, accurate data collection of effective moisture diffusivity should be viewed as a major objective in pasta drying research.

공항 콘크리트 포장 설계를 위한 환경하중 산정방법 개발

콘크리트 포장의 환경하중은 온도하중과 수분하중으로 구분할 수 있으며, 이는 콘크리트 슬래브 내의 온도분포와 건조수축 및 크리프를 의미한다. 본 연구에서는 공항 콘크리트 포장의 역학적 설계에 필요한 환경하중을 산정할 수 있는 방법을 개발하였다. 먼저, 대상 지역과 설계 슬래브 두께를 결정한 후, 포장 온도 예측 프로그램을 사용하여 예측된 슬래브 깊이에 따른 콘크리트 온도분포를 등가선형 온도차이로 환산하였다. 기존 건조수축 예측 모형을 개선하여 지역별 상대습도를 고려하여 콘크리트의 건조수축을 예측한 후 부등건조수축 등가선형 온도차이로 환산하였다. 또한, 응력이완을 건조수축에 반영하였다. 결국, 온도에 의한 등가선형 온도차이와 수분에 의한 부등건조수축 등가선형 온도차이를 합하여 최종 환경하중인 총 등가선형 온도차이를 산정하였다. 적용 예를 보이기 위해 지역별 기상조건을 대표할만한 국내 민간공항 8곳 및 군공항 2곳의 환경하중을 본 연구에서 개발된 방법으로 계산하고 비교하였다. The environmental load of concrete pavement can be categorized by temperature and moisture loads, which mean temperature distribution, and drying shrinkage and creep in the concrete slab. In this study, a method calculating the environmental load essential to mechanistic design of airport concrete pavement was developed. First, target area and design slab thickness were determined. And, the concrete temperature distribution with slab depth was predicted by a pavement temperature prediction program to calculate equivalent linear temperature difference. The concrete drying shrinkage was predicted by improving an existing model to calculate differential shrinkage equivalent linear temperature difference considering regional relative humidity. In addition, the stress relaxation was considered in the drying shrinkage. Eventually, the equivalent linear temperature difference due to temperature and the differential shrinkage equivalent linear temperature difference due to moisture were combined into the total equivalent linear temperature difference as terminal environmental load. The environmental load of eight civilian and two military airports which represent domestic regional weather conditions were calculated and compared by the method developed in this study to show its application.

Three-dimensional shape transformations of hydrogel sheets induced by small-scale modulation of internal stresses

Although Nature has always been a common source of inspiration in the development of artificial materials, only recently has the ability of man-made materials to produce complex three-dimensional (3D) structures from two-dimensional sheets been explored. Here we present a new approach to the self-shaping of soft matter that mimics fibrous plant tissues by exploiting small-scale variations in the internal stresses to form three-dimensional morphologies. We design single-layer hydrogel sheets with chemically distinct, fibre-like regions that exhibit differential shrinkage and elastic moduli under the application of external stimulus. Using a planar-to-helical three-dimensional shape transformation as an example, we explore the relation between the internal architecture of the sheets and their transition to cylindrical and conical helices with specific structural characteristics. The ability to engineer multiple three-dimensional shape transformations determined by small-scale patterns in a hydrogel sheet represents a promising step in the development of programmable soft matter.

Troubleshooting coextrusion film problems by considering process–property relationships*

Coextrusion of plastics into a multilayer film is a complex process where many processing and structure design factors affect performance. As a result, problems can be difficult to troubleshoot. We describe issues involving estimating properties from monolayer films, achieving good interlayer adhesion and minimizing curl. Multilayer film properties such as gas permeation and bending stiffness cannot be estimated from simply adding up the properties of monolayer films of the individual layers. Properties may also differ from their monolayer analogs due to differences in stress and temperature history during coextrusion. Some combinations of polymers may not be possible to make due to flow instabilities. Many polymers used in multilayer films do not adhere well to one another. Tie resins have been developed to promote adhesion, but many factors affect their peel strength performance, including fabrication parameters. More so than monolayer films, coextrusion films are prone to curling or rolling up on themselves. Factors such as differential shrinkage during quenching play a role. This paper explores some of the recent advances in the science of coextrusion and how this knowledge can be used to address these issues.

Modeling kinetics of distortion in porous bi-layered structures

Abstract Shape distortions during constrained sintering experiment of bi-layer porous and dense cerium gadolinium oxide (CGO) structures have been modeled. Technologies like solid oxide fuel cells require co-firing thin layers with different green densities, which often exhibit differential shrinkage because of different sintering rates of the materials resulting in undesired distortions of the component. An analytical model based on the continuum theory of sintering has been developed to describe the kinetics of densification and distortion in the sintering processes. A new approach is used to extract the material parameters controlling shape distortion through optimizing the model to experimental data of free shrinkage strains. The significant influence of weight of the sample (gravity) on the kinetics of distortion is taken in to consideration. The modeling predictions indicate good agreement with the results of sintering of a bi-layered CGO system in terms of evolutions of bow, porosities and also layer thickness.

Performance Criteria to Assess Shrinkage Cracking Tendency in Concrete Overlay

Abstract Differential shrinkage between new concrete overlay and that of old substrate concrete will trigger shrinkage (tensile) stress leading to cracking when this tensile stress development reaches tensile capacity of overlay. There are many parameters affecting the magnitude of shrinkage stress. Any criteria used to assess cracking tendency of concrete overlay caused by differential shrinkage should take into account all of the parameters involved in building up shrinkage stress. Assessment of shrinkage cracking behaviour of concrete overlay could be classified into qualitative and quantitative method. This paper reviews both methods. Current models for estimating shrinkage stress and their possible application for setting performance criteria to assess shrinkage cracking tendency in concrete overlay are discussed. Simplification of model is proposed and extension of data to improve the model is suggested.

가압-진공 하이브리드 주입성형에 의한 알루미나의 균질 성형

Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates owing to disadvantages of these processes, such as the high cost of the equipment, the formation of density gradients, and differential shrinkage during drying. These problems can be avoided by employing a pressure-vacuum hybrid slip casting approach that considers not only by the compression of the aqueous slip in the casting room (pressure slip casting) but also the vacuum sucking of the dispersion medium (water) around the mold (vacuum slip casting). We prepared the alumina formed bodies by means of pressure-vacuum hybrid slip casting with stepwise pressure loading up to 0.5 MPa using a slip consisting of 40 vol% solid, 0.6 wt% APC, 1 wt% PEG, and 1 wt% PVA. After drying the green body at 30℃ and 80% RH, the green density of the alumina bodies was about 56% RD. The sintered density of an alumina plate created by means of sintering at 1650℃ for 4 h exceeded 99.8%.This method enabled us to fabricate a 110 × 110 × 20 mm alumina plate without cracks and with a homogeneous density, thus demonstrating the possibility of extending the method to the fabrication of other ceramic products.