External Shrinkage Research Articles

Collagen dehydration

Type I collagen is a ubiquitous structural protein in animal tissues. It is normally present in a hydrated form. However, collagen is very dependent on associated water for its mechanical properties. In skin, where type I collagen is dominant, there is a longstanding concern that the skin and therefore collagen may partially dry out and result in structural degradation. Here we show that dehydration of type I collagen fibrils, using 2-propanol, results in a two-stage dehydration process. Initially, the fibrils do not change length, i.e. the D-period remains constant, but shrinkage occurs within the fibrils by an increase in the gap region and a decrease in the overlap region within a D-band and a shortening of the helical turn distance and fibril diameter. Only with further dehydration does the length of the collagen fibril decrease (a decrease in D-period). This mechanism explains why collagen materials are resistant to gross structural change in the early stages of dehydration and shows why they may then suffer from sudden external shrinkage with further dehydration.

A Study on the Recreated Experiment and Casting Method of Ancient Iron Seated Buddha by Spilt Casting Method

The study aimed to investigate the split casting method based on the recreation of the iron-seated Buddha (ISB) statue (number 1971) in the Chuncheon Museum. The statue was designed using three-dimensional scan data and reduced to half-size. Using the existing research results, the ISB statue was created by mold production and split casting. The mold was prepared by mixing sand and clay at a ratio of 3:4 and 1:3 on the outside and inside, respectively, and then casting was done. Various casting defects were observed in the ISB casting and similar shapes were seen. The casting defects included veining or finning, misrun, open or external shrinkage, surface or subsurface blowholes, surface pinholes, and shift. The microstructures were identified as branch-shaped dendrite and pearlite organizations, and black graphite was observed between the cementite organizations. The study findings may be relevant in exploring traditional casting and manufacturing techniques of ISB and may aid in the production of the original form of ISB.

Plastic and early-age shrinkage of ultra-high performance concrete (UHPC): Experimental study of the effect of water to binder ratios, silica fume dosages under controlled curing conditions

The magnitude of early age shrinkage of Ultra High Performance Concrete (UHPC) is markedly different from normal and high strength concretes. A series of experiments were performed to determine the influence of water to binder ratio and silica fume content on the rate of hydration, stiffness development, chemical and external shrinkage under both sealed and unsealed conditions. Experimental apparatus, designed for shrinkage in normal strength concretes, were adapted to accommodate the larger volume changes and minimise the influence of boundary restraint. Continuously monitored internal temperature, and relative humidity conditions, along with periodic measurements of hydration degree and stiffness are used to elucidate the volumetric deformation mechanisms. Results, from as early as three hours after water addition demonstrate significant volumetric changes occurring in the early plastic state of the material.

Influence of Al-B grain refiner on porosity formation of directionally solidified Al-Si alloys

This work aims to present a perspective for porosity formation in three different alloys: A356, A413 and A380.1 by taking into account the addition of Al-B grain refiners: AlTi5B1 and Al3B. The directional solidification method was used, and microstructural changes of the alloys and its correlation with porosity formation were investigated. Pore size, number of pores, average pore length and distribution of pores were statistically analyzed. Also, external shrinkage was examined, and the volume of external shrinkage was calculated. It was found that there was a relationship between external shrinkage and the size and number of pores. As the size and number of pores internally decrease, external shrinkage increases. Additionally, porosity is decreased in all the three Al-Si alloys when Al-B grain refiners are used. The distribution of pore diameters is low when AlTi5B1 is used. Grain refiners have a different effect on porosity formation of Al-Si alloys with regard to their solidification morphology.

Establishment of Casting Manufacturing Technology by Introducing an Artificial Sand Mold with Furan Resin and Realizing a Clean Foundry

In general, the working environment of foundries is bad, compared to other manufacturing industries. To improve this, dust collection facilities are installed or improved. However, they cannot be installed in some factories. Therefore, we attempted to change the sand type from natural silica sand to spherical artificial sand mold with furan resin to improve the working environment. Before switching, we investigated the problems that occur when switching to artificial sand and external shrinkage problems were found. After taking countermeasure against the problem, we changed the sand type. As a result, it was possible to reduce the amount of dust in the working environment, and the control class prescribed by the Ordinance on Prevention of Dust Hazard could be reduced from level 3 to level 2.

Optimization of welding loads with narrow groove and application of modified spray arc process

Current efforts for lightweight design result in a growing application of high-strength fine-grained structural steel in modern constructions, e.g. mobile cranes, with yield strength from 960 MPa. The design of welded structures and welding processes becomes more challenging with increasing material strength and elastic ratios. High residual stresses are able to diminish lifetime, load capacity and component safety and should be avoided. Recent analyses have shown strong influences of heat control and restraint of the weld due to arising reaction stresses, superimposing with local residual welding stresses. Modern inverter technologies allowed the development of numerous modified spray arc processes driven by power source manufacturers, which provide virtually similar features and several benefits, enabling welding of narrower seams with reduced weld volumes and total heat inputs. This research focuses on welding loads due to modified weld seams. The global reaction forces and moments and their superposition with local residual stresses in welded components due to external shrinkage restraints were investigated using a special testing facility and XRD. The restraint intensity, weld seam geometry and welding process were varied for statistical evaluations of resulting welding loads. When welding under restraint, a reduction of the weld seam volume causes significantly lower reaction stress levels.

Controlled Precipitation Gaseous Cavities in Aluminium Castings

Abstract At thermal junctions of aluminium alloy castings and at points where risering proves to be difficult there appear internal or external shrinkages, which are both functionally and aesthetically inadmissible. Applying the Probat Fluss Mikro 100 agent, which is based on nano-oxides of aluminium, results in the appearance of a large amount of fine microscopic pores, which compensate for the shrinking of metal. Experimental tests with gravity die casting of AlSi8Cu3 and AlSi10Mg alloys have confirmed that the effect of the agent can be of advantage in foundry practice, leading to the production of castings without local concentrations of defects and without the appearance of shrinkages and macroscopic gas pores. Also, beneficial effect on the mechanical properties of the metal has been observed.

Modeling of shrinkage defects during solidification of long and short freezing materials

The aim of the model presented in this paper is to capture the difference in solidification behavior of long and short freezing materials. The shrinkage defects in short freezing materials tends to be internal, as porosity, while in long freezing materials these defects tend to be external in the form of surface depressions. To achieve this, a pressure drop based 3D feeding flow model has been developed to evaluate shrinkage defects for casting alloys. A continuum formulation is used to describe the transport of mass, energy and momentum. It is assumed that during solidification the driving force for flow is shrinkage. A Darcy type source term has been included in the momentum equation to account for flow resistance in the mushy zone. A VOF free surface model has been used to describe shrinkage defects, i.e., external surface depressions and internal shrinkage porosities, while ensuring mass conservation. The model is used to calculate the shrinkage in a simple casting. The results shows internal and outside shrinkage defects depending on the freezing range of the metal. Short freezing range results mainly in internal shrinkage whereas the long freezing range results in external shrinkage. The expected shrinkage features are well described by the present model.

Model for prediction of shrinkage defects in long and short freezing range materials

The present paper presents a three-dimensional model that is capable of predicting the pressure drop due to shrinkage. The model is based on fluid flow calculation considering a drag force (Darcy term) that is function of fraction solid and on the external surface resistance to move. It considers external defects, in the form of surface depressions, and internal shrinkage defects. By coupling the feed flow, pressure and solidification calculation for predicting shrinkage defects, a complete methodology that enables the possibility to show dynamic shrinkage geometry in the casting and feeding system is presented. To put in evidence the difference morphology of these defects, the behaviour between long and short freezing range aluminium alloys was compared. The model is used to calculate the shrinkage in a simple casting which is composed by a feeding system and blocks with different necks. Two kinds of aluminium alloys, a long freezing AlSi7 and a short freezing AlSi12 are used. The results show internal and outside shrinkage defects depending on the freezing range of the metal. Short freezing range results mainly in internal shrinkage whereas the long freezing range shows more external shrinkage. The expected shrinkage features are well described by the present model.

Effects of the Load History on the Residual Stress Distribution in Welded Components

The lifetime of a welded component is finally influenced by the various service conditions. The stress redistribution effect of subsequent load histories is fundamental to the load-bearing capacity of a structure later in service. Since every welded structure additionally experiences external shrinkage restraint, the resulting structural loads are very important for mechanical assessment. Forward-looking development of materials furthermore requires particular consideration of in-service load histories and of their effects on the global structural loads of a construction under shrinkage restraint. Using a large-scale test facility, stress and residual stress investigations have been performed relating to the subject area of residual stress redistribution resulting from a simulated load history. Based on the presented results, which were all carried out with matching filler materials, further research work concerning the influence of the variation of the mismatch factor on the residual stress distribution has to be done.

The effect of grain refinement on the formation of casting defects in alloy 356 castings

One of the main reasons for rejection of wheel castings is the formation of shrinkage defects at the spoke-rim junction. Industrial trials show that the severity of defects is accentuated by the addition of grain refiner beyond an optimum level. Subsequent laboratory castings also found that the addition of grain refiners beyond this optimum level increased the size of the defect at hot spots in a casting. This is explained by a decrease in the size of interdendritic channels during feeding when the grain size is reduced. Therefore feeding becomes restricted earlier in grain refined castings and thus a larger amount of shrinkage needs to be accommodated in the hot spot. It was also observed that when plentiful fresh oxide films are present then the nucleation of porosity is favoured. However, when fresh oxide films have not been generated, then external shrinkage (slumping of the casting surface) is more likely to occur.

Shrinkage-related degrade and its association with some physical properties in Eucalyptus regnans F. Muell

Assessments of internal checking and the physical properties of 124 trees of Eucalyptus regnans F. Muell. have shown that for material dried under relatively mild predryer conditions (30 °C, 65% RH) internal checking was highly positively correlated with each of collapse, moisture content and normal shrinkage, and weakly negatively correlated with total external shrinkage. Collapse alone explained 47% of the variation in internal checking. Incidence of internal checking in sample boards could be estimated with moderate success by each of the following properties measured on board ends: collapse, the number of internal checks and initial moisture content. Material with high mean basic density above 530 kg/m3 was associated with low levels of internal checking and collapse. However, the maximum naturally occurring density of E. regnans was not high enough to obviate collapse and internal checking. It was observed that growth rings in 100 × 50 mm backsawn boards in which the earlywood air-dry density was below 450 kg/m3 showed internal checking. The size and number of internal checks increased with a decrease in earlywood density. It was shown that drying E. regnans below temperatures of 24–30 °C does not eliminate collapse, thus raising doubt about the validity of a temperature threshold concept in that range.

Development of a new experimental technique for the study of the autogenous shrinkage of cement paste

After defining and describing the main physicochemical mechanisms governing the autogenous shrinkage of concrete, a number of different experimental approaches used to asses this phenomenon are discussed. The base principle and a detail description of a new experimental technique aiming to completely characterise the autogenous shrinkage of a cement paste are presented. The originality of the technique comes from the fact that the variation of the external volume (external autogenous shrinkage) and the volume of the gasfilled spaces in the liquid phase after the hardening (internal autogenous shrinkage) are measured separately and simultaneously. The total autogenous shrinkage is the sum of the internal and external autogenous shrinkages. A number of experimental results are presented to demonstrate the validity of the proposed experimental approach and to analyse the effect of water/cement ratio on the development of internal and external shrinkages.

Shrinkage of Oil Well Cement Slurries

Abstract Gas leakage into and through the cemented annulus in oil and gas wells is a safety problem. The conditions for gas migration develop when the hydrostatic pressure of the hydrating cement slurry column slowly declines and finally falls below the pore pressure of a gas bearing formation. This pressure decline is mainly caused by chemical shrinkage of the cement. A low shrinkage will reduce the pressure decline and hence the risk of gas migration. A new and simple method for measurement of total chemical shrinkage at high temperatures has been developed. It has proved to be reliable and sensitive for monitoring the cement hydration process. The equipment was used to show that there is a marked difference in shrinkage behaviour for the tested slurries up to 180 ° C, probably due to a temperature effect on the cement hydration chemistry. The results confirmed the correlation between total shrinkage and cement content, and thus it follows that using more extender will reduce the likelihood of gas migration. Introduction Cement slurries are used in oil and gas wells for cementing the steel casing to the wellbore and thus sealing the rock formations from the well. Gas leakage into and through the cemented annulus is still a problem, in particular where shallow gas sands are penetrated and in deep gas wells, i.e., under high temperature and high pressure (HTHP) conditions. The leakage may manifest itself either as vertical communication between permeable gas reservoirs or migration all the way to the surface. Gas pressure in excess of the cement hydrostatic slurry pressure is the driving force behind gas migration. Reasons and mechanisms of gas migration are discussed by Levine et al.,(1) Sabins et al.(2), and Cheung and Beirute(3). Annular gas flow may be initiated when the hydrostatic pressure of the cement slurry declines and falls below the pore pressure of a gas bearing formation due to the combined effect of shrinkage, fluid loss to the porous well bore and gel strength build up. Normally a slurry volume reduction would be compensated for by contraction and downward movement of fluids from above, thus maintaining its hydrostatic head. However, during the setting process the cement slurry develops a gel structure causing it to stick to the wall thus hindering compensation of the shrinkage. The second requirement for gas migration is that the cement must enable gas flow into the cement either by permeability, channels, microannuli or microfractures before the slurry has reached a sufficient strength. Thus, the gas migration phenomenon is thought to be initiated during the transition state, from being fluid to becoming hard, i.e., between initial and final set of the cement. A low shrinkage is preferable because the resulting hydrostatic pressure decline will be lower than for a slurry with high shrinkage, i.e., pressure equilibrium between gas and slurry column is reached at a later point of time. The chemical shrinkage may be divided into two parts: external shrinkage and total shrinkage.

Solidification shrinkage in metal matrix composites

A new test is described using simple unfed cast discs which allows a quantitative assessment of the shrinkage behaviour of cast materials in terms of (i) internal or external porosity and (ii) concentrated or dispersed porosity. The test has been applied to two different particulate metal matrix composites, and an aluminium alloy (Al—7% Si—0.4 Mg) which was common to both as the matrix alloy has also been investigated. One composite contained 7 vol% TiB2 particles and the other contained 20 vol% SiC particles. The shrinkage behaviour of the MMCs was found to be different from that of the matrix alloy. For higher section thickness castings, the matrix alloy alone developed a concentrated central shrinkage cavity, whereas the MMCs showed different behaviour. A large amount of external shrinkage was generated in TiB2 MMC, while the amount of internal shrinkage was small. For the SiC MMC, the internal and external shrinkage was similar. Generally, the internal porosity in both MMCs was found to be finer and more uniformly dispersed. The reason for the greater proportion of internal porosity in the SiC MMC compared to its TiB2 equivalent appears to be associated with the partly non-wetted surfaces of the SiC particles, whereas the chance of pore nucleation on well-wetted TiB2 particles (formed by chemical reduction in the melt) was very low. The level of internal porosity in thin-section castings was low (approximately 0.5%) for all cast materials in this study, and even for heavy sections in the cast MMCs the porosity would be tolerable for many components because it was dispersed and therefore would not by itself cause a casting to leak.

Internal and external shrinkages in unidirectionally solidified Al4.5wt.%Cu alloy

Abstract Solidification shrinkage and macrosegregation were investigated in Al4.5wt%Cu alloy ingots solidified unidirectionally upwards from the bottom. Large external shrinkage was generated, while the amount of internal shrinkage (porosity) was small. The amount of external shrinkage increased with increasing distance from the bottom and with decreasing temperature gradient in the ingots. Inverse segregation, which usually occurs in unidirectionally solidified ingots, was not severe in the present work. This was because when the top of the ingot reached a pasty state, the capillary pressure acting on the liquid made it impossible for the interdendritic liquid to flow downwards to compensate for the solidification shrinkage, and the major part of the solidification shrinkage was compensated for by the formation of external shrinkage. The amount of solidification shrinkage and the degree of macrosegregation in the ingots were computer simulated and compared with the experimental results.

Calcium Storage in Face Fly (Diptera: Muscidae) Larvae for Puparium Formation1

The Malpighian tubules are shown to be the main storage site for Ca and other elements for puparium formation by the face fly, Musca autumnalis De Geer. Calcium in the anterior Malpighian tubules is stored in the form of amorphous, layered spheres 0.4 μm to >10.0 μm in diameter. Major elements in the composition of these spheres were Ca, P, and Mg, with traces of K. The weight of the tubules' content increased during the prepupal period. A major decrease then occurred and continued through the pupal period. The decrease results from movement of mineralized elements from the spheres and corresponds with the first significant amount of Ca and P found in the cuticle of the puparium. Mineralized spheres undergo dissolution in the proximal portion of the anterior Malpighian tubules, as indicated by external shrinkage and dissolution of internal layers, probably by changes in pH or enzymatic action.

Sintering characteristics of coal ashes by simultaneous dilatometry-electrical conductance measurements

Two different experimental procedures were used to investigate the sintering characteristics of coal ashes on heating. First, the Leitz heating microscope was used to record the shrinkage of an ash pellet and the electrical conductance was measured by inserting two platinum wire electrodes into the sample carrier. Another furnace assembly was also constructed where the shrinkage of the ash compact was monitored by a linear displacement transducer, and the conductance of the sample was measured between two platinum disc electrodes. Usually the results are consistent with a sintering model based on the precept that the development of a sinter bond between the particles is accompanied by the external shrinkage of the ash compact and by the increase of the conductance.

Relation between Shape of External Shrinkage Defect and Solidification Expansion Curve for Spheroidal Graphite Iron Castings

Relation between Shape of External Shrinkage Defect and Solidification Expansion Curve for Spheroidal Graphite Iron Castings