End Cracking Research Articles

Assessing Treatments to Mitigate End-Face Cracking in Air-Dried Acacia dealbata Logs

Acacia dealbata Link, known as Mimosa in Portugal, is an invasive hardwood species with potential for construction use, but research is limited. The available stock of small-diameter juvenile wood logs can help reduce this gap, but tangential cracking at log ends challenges fastener connections. This study evaluated different treatments to control and reduce end-face cracking in small wood logs during air drying, an economical and environmentally friendly procedure. The extreme two-thirds of sixteen Mimosa logs were subjected to two treatments: one with longitudinal kerfs 15 mm deep along the length (two and three kerfs) and the other with a hollow in the center up to half the length (16 mm and 30 mm diameters). Over 219 days of air drying and compared with the central part, kerfing treatments significantly reduced outer-wood tangential cracking (p < 0.001), with the three kerfs also reducing crack numbers (p < 0.05) but increasing significantly cracks near the pith (p < 0.01). The 30 mm central hollow significantly reduced central perforation cracking (p < 0.05). Prospectively, the results suggest that a combined treatment approach involving cross-cuts could help reduce and/or control end cracking, thereby improving the suitability of wild Mimosa logs for construction use.

Evaluation of the Performance of Expanded Polystyrene Block on the Reduction of the Deck Cracking in Wide Integral Abutment Bridge

Longitudinal joints are thought to provide relief from expansion and contraction of the bridge deck owing to temperature change, shrinkage, and live loads, especially for a wide bridge. Historically, however, these joints have been known to leak, allowing chloride-laden water to reach the bottom of the deck overhang and even the exterior girders. Research conducted by Phares et al. indicated that the development of cracking in bridge decks seems less dependent on the total width of the deck and more so on internal restraint of the abutment to temperature changes and, in particular, gradients. Based on the finite element method (FEM) results, an effective solution to reduce cracking in the deck might be to place an isolation pad between the soil and the back side of the abutment. The primary objective of this paper is to investigate the effectiveness of an isolation foam block at the back of an integral abutment in reducing the stress-induced strain and the deck end longitudinal and diagonal cracking near the end of the deck with an integral abutment. To achieve this objective, a highway bridge (Viking Road Bridge) in Iowa, US, designed with a width of 228 ft, was selected for the study. The bridge deck has no longitudinal joints but, based on the previous research results, it was equipped with thermal isolation pads behind the abutment. The newly constructed bridge was monitored for over two years, and this was followed by multiple bridge inspections. An analytical study was conducted to investigate the efficiency of the isolation foam on the bridge deck end structural behavior. The results indicated that the thermal isolation foam is effective in reducing the temperature gradient through the abutment thickness, especially on extremely cold days. By reducing the temperature difference between the abutment and the deck, a thermal isolation block is effective at reducing the deck end strain and resisting deck end cracking. The FEM results indicated that the maximum deck stress-induced strain was 46% greater without the effects of the thermal isolation block and greater than the concrete cracking strain. This indicated that, without the thermal isolation pad, the Viking Road Bridge could crack at the end of its deck.

Numerical study on the temporal changes of the principal stresses at the ends of the hollow PC-girders to control horizontal end cracks

Background/Objectives: To professionally meet bridge load demands, hollow PC-girders are recently considered for bridge construction, particularly in Japan. Hollow girders are pretensioned girders, which can be a good alternative for ordinary PC-girders by having lightweight, using less material than other beams, and spanning long distances. Hollow PC-girders can be vulnerable to horizontal end cracking at the time of prestressing strand release. Methods: In this study, a nonlinear finite element analysis was performed to investigate the occurrence of horizontal cracks at the time of prestressing at the ends of hollow PC-girders. First, the selected hollow girder was miniaturized to a span length of 4 m required for sufficiently prestressing; then, a standard static prestressing analysis was performed using a finite element analysis software Midas FEA. This software is an analysis tool with standard FEM analysis functions in the construction field and can perform detailed analysis for reinforcements and concrete crack analysis. The software was used to model the girder and investigate the temporal changes of principal stresses at hollow PC-girders’ ends. Findings: The study showed that placing only end-zone reinforcements cannot reduce principal stresses to the level to be less than the concrete’s tensile strength. However, debonding four PC-strands at the ends of the girder alongside the placement of end-zone reinforcements could sufficiently reduce principal stresses to the level to be less than the tensile strength of concrete, and consequently, horizontal cracks were eliminated at the ends of the hollow PC-girder. Keywords: Horizontal cracks; pretensioned girders; hollow PCgirders; finite element analysis; Midas FEA

A digital control system designed for ore thermal furnaces producing metallurgical silicon

This paper considers the key control issues related to non-adjustable parameters in the production of metallurgical silicon in ore thermal furnaces. A series of experiments has been conducted to confirm the possibility of introducing the electrode off-position control. Thus, additional control parameters were introduced in the process control system. The electrode positioning algorithm was tested and adjusted to minimize electrode bending and reduce the risk of breakage and to minimize end cracking and spalling during restarting in the current production environment. An integrated 3D model of the thermal field distribution has been developed and built that accounts for the charcoal moisture content, the position of the electrodes and the power emitted as the charge gets hot. Substantiation is given to the application of this adaptive adjustment algorithm to control the changing parameters as determined by the process conditions, such as the moisture content of the charge, the position of the electrode, the power mode of the furnace. The authors propose to expand the existing control system by adding a digital module, i.e. due to the integration of electrode off-position signals and the use of the adaptive adjustment algorithm and avoiding using any additional corrective signals. This research was carried out as part of the Governmental Assignment No. 075-03-2020-127/1 for the year of 2020, Project No. FSRW-2020-0014. Subject: A crossdisciplinary approach to the comprehensive exploitation of natural resources and conservation. Area (a 2020 topic): “Comprehensive processing of minerals and man-made materials and gasification of solid hydrocarbons: A review and concept elaboration”. As greenhouse gases and carbon are produced as a result of electrode destruction, it is proposed to use the method of gasification and dispose of the heat produced.

Comparison of Seasoning Defects due to Different Kilns and Kiln Schedules for Teak

Timber is one of the major construction material in Sri Lanka and timber seasoning is a common practice for achieving dimensional stability. The industry uses timber for interior and exterior joinery work such as doors, windows, door and window frames and panelling. However, forming seasoning defects is a common issue which prevalent in this industry. Therefore this study is conducted to identify defects caused by seasoning for teak timber and to find out solutions. For this reason, there different kilns located in Biyagama, Horana and Kottawa, operated under different schedules were selected. The impacts of three schedules were tested using teak planks. Kiln temperature and moisture content were measured for the entire seasoning period. Cupping, twisting and end cracking were measured as defects. Moreover, prong test was also conducted to determine the stress condition of the dried wood samples. Among the selected kilns, only one was maintained under the operating parameters recommended by the kiln manufacturer. The results revealed that the kiln which was programmed to regulate temperature produced the least amount of defects. However, moisture content was not programed for any of the kilns. Therefore it can be concluded that temperature has more impacted on causing defects on timber drying in the seasoning period. Therefore it is essential to regulate the temperature as per with kiln schedule. Keywords: Construction industry, Timber identification, Seasoning issues, Kiln drying

ANALYSIS OF STRAIN STATE AND CRACKING OF COCNRETE SLEEPERS

Prestressed concrete sleepers are the most common type of the sleepers used on the railroad. They serve as rail supports and absorb loads induced by trains. Sleepers are important for the durability and safety of the railroad and are exposed to various loads and an agressive environment during exploitation. Therefore, different types of appearing damage can determine their reliability. The article briefly discusses possible causes of damage and the deterioration of prestressed concrete sleepers. End cracking and damage at the rail seat was determined during the inspection of used sleepers. Therefore, the strain state and cracking of the rail seat of the sleeper was analysed under static and dynamic loads. The paper provides the obtained results of experimental research of used and new sleepers.

Study of End Cracking during One-Sided Submerged Arc Welding with Flux-Copper Backing

Longitudinal hot tearing, popularly called as end cracking, frequently takes place in the end portions of large steel panels’ butt joints, using one-sided, submerged-arc welding with flux copper backing welding process (FCB welding). The study was to look for the possibility to improve and/or prevent the end cracking issue during FCB welding, center blind-hole drilling technique was used to measure the welding residual stress for five different cases, considering hot tearing mechanism, its influence factors and the relevant reported prevention measures. Unpredictable result was observed subsequently that transverse compressive stress is found on the shallow surface of weld seams, which could give supplementary information to the common assumption for conventional low heat input welding method that cracks initiation is caused by tensile stresses across the welded joints. The study concluded that FCB welding end cracking issue is caused by the comprehensive function of different stresses, and also properly use tack welding practice, suitable elastic run-off plate and relatively low heat input energy which will reduce the end cracking susceptibility for the tested materials.

Influence of Initial Wood Quality and Drying Process on Utilization Grades of Sawn Spruce Timber

European spruce (Picea abies Karst.) belongs to the most easily dried wood species, but nevertheless cracking and warping often reduce the quality of dried sawnwood. Larger surface and end cracking was noticed at industrial drying practice in cold winter season, especially in using fast drying schedules. For the assessment of factors infl uencing the quality of dried wood some drying runs with varying drying conditions were carried out in an experimental kiln dryer. The quality of sawnwood was evaluated on green material using standard procedures and compared with the quality at the end of drying processes. Drying of spruce sawnwood at sharper drying conditions was more risky, resulting in a larger number of cracks as well as larger fi nal MC distribution, larger MC gradients and casehardening. Additionally, signifi cant correlation was confi rmed between the quality of dried wood and input quality of fresh material. More downgrading after the drying was observed in case of initially low graded material.

Investigation of end cracking and its prevention by a double reduction die in the cold extrusion of automotive parts

End cracking failures occur randomly during cold extrusion of automotive shafts or sometimes even during service. Finite element analysis of this failure shows that cracking is primarily due to a combination of damage during cold deformation and tensile unloading at the exit of the die land. This paper proposes a failure mechanism and a stress-based failure criterion for this cracking. It analyses the original single die design and investigates a double reduction die design, which was patented for the extrusion of brittle materials. It is seen that while the double reduction die reduces end cracking, it increases the probability of chevron cracks at the part centre. Finally, a design of experiments technique is used for determining the optimum die design parameters for the minimum tensile stress state both at the surface and at the billet centre. Production validation experiments confirm the efficacy of the optimal die design in suppressing the initiation of end cracks without the need for special billet shearing or annealing procedures.

Release Methodology of Strands to Reduce End Cracking in Pretensioned Concrete Girders

Results of numerical and experimental investigations concerning the causes of prestressed concrete girder end cracks are reported in this paper. The cracks, which developed during the flame-cutting release process, resulted from the restraining effect of unreleased strands as the girders shortened from the partially transferred prestress and from shear stresses generated by the cutting order of the strands. Several methods were examined to eliminate the cracks, including changes to the strand cutting pattern, debonding some of the strands in the end regions, and increasing the slope of the top surface of the bottom flange. The first two of these methods were implemented in the field and found to be successful.

083 FRUIT HYDRAULIC BUDGETS IN FRENCH PRUNE (PRUNUS DOMESTICA L. CV. FRENCH) AND THEIR EFFECTS ON FRUIT GROWTH AND CRACKING

End cracking of French prune fruits occurs when previously water stressed trees are irrigated during early July. Fruit phloem, xylem and transpiration flows (P, X and T, respectively) were measured diurnally during 72 h periods in mid June, early July and mid July (before, during and after the crack-susceptible period). Midway through each 72 h period, the previously stressed trees were irrigated. In mid June, X was larger than P, whereas P was larger than X during early July. In mid July, P and X were similar. In early July, the period preceding irrigation was characterized by an ourflow of phloem sap during the day and phloem inflow during the night. After irrigation, larger phloem inflows were observed and no phloem outflow occurred. Fruit transpiration rates were highly correlated with VPD. They exhibited a gradual decrease during the season, reaching minimum values during early July, before increasing again. The sum of P and X was virtually identical for the three periods i.e. stronger P's compensated for weaker X's and vice versa. Our results suggest that properties intrinsic to the fruit play the primary role in modulating water and photosynthate movements between the tree and the fruit. The possible role of these properties on fruit growth and cracking will be examined.

Water Relations of Fruit End Cracking in French Prune (Prunus domestica L. cv. French)

Irrigation of previously water-stressed French prune trees is known to induce fruit end cracking. The relationships between end cracking, water relations, and mechanical properties of the skin of French prune were studied as a function of irrigation regimes under field conditions. Water stress resulted in the accumulation of solutes in the fruit of nonirrigated trees. A gradient in osmotic potential (ΨS) existed along the vertical axis of fruit from all treatments; ΨS was always lower at the stylar than stem end. Irrigation of previously water-stressed trees (irrigated-dry treatment) resulted in ΨS gradients exceeding those of all other treatments. Moreover, estimated turgor (ΨP) at the stylar end of the fruit increased 2-fold within 24 hours after irrigation. These changes were accompanied by the onset of fruit end cracking, and neither the well-watered controls nor the continuously droughted fruit exhibited such changes. During the 24 hours following irrigation, the overall ΨS of irrigated-dry treatment fruit was diluted by the same amount as the calculated increase in fruit volume. However, during the same period, ΨS at the stem end of the fruit showed more dilution than expected, and ΨS at the stylar end of the fruit concentrated, indicating a redistribution of solutes. There were no differences in skin mechanical properties along the fruit vertical axis and, hence, this could not have accounted for the observed changes in ΨS and ΨP. Thus, when previously stressed French prune trees were irrigated, the overall recovery in water potential (Ψ) and the subsequent movement of solutes to the stylar end of the fruit resulted in apparently excessive turgors in this region and hence the observed pattern of end cracking.

Simulation of Welding Deformation for Accurate Ship Assembling

It is essential to predict precisely the welding deformation of hull structures at assembly stage, to built accurately ship blocks and to increase productivity through mechanization/automation effectively.At a first step of the studies, a practical system applied for production engineering was proposed to simulate in-plane deformation of one side automatic welding of the panel, with an analytical model using finite element method solving unsteady heat conduction problem and thermal elastic-plastic behavior.Some parametric studies were carried out using this numerical simulation system and also experimental measurements : (1) The distribution of the shrinkage across the butt weld is affected mainly by residual stresses due to tack welding, fitting of tab plate and so on.(2) Some countermeasures to prevent end cracking in one side welding, such as local heating in the vicinity of the plate edge and changing of welding sequence, affect also the distribution of the shrinkage, while pitch of tack weld beads, type of tab plate and root gap have less effect.

End cracking during one-sided submerged-arc welding

Abstract The mechanical behaviour of end cracking during one-sided SAW was computer-simulated by thermal elastic analysis with the introduction of a dummy element. Experiments on small sized specimens and on-site large specimens have been carried out. The rotational deformation, the mechanism of formation of the end cracking and factors affecting it were investigated. It was concluded that for preventing the formation of end cracks, the end opening displacement and the rate of end opening should be reduced as far as possible. Theoretical analysis and on-site large specimen experiments showed that end cracking can be effectively prevented only if the arrangement of tack welds over the weld end is appropriate, and the stiffness and restraint of slit tab plate are moderate. By the aid of the above mentioned study, end cracking was successfully avoided in over 130 specimens of 12, 14, 16, 18 and 20mm thickness with weld length more than 1000m.

Studies on Transient Stresses and Deformation Behavior of Groove due to Butt-Welds of Thin Mild Steel Plates (3rd Report)

In the previous reports, it has been shown that transverse forces acting on tack welds and deformation behavior of groove during butt-welding varied with sizes of welded plates and welding conditions significantly. The purpose of this report is to clarify effects of plate width, length of weld, tack weld pitch and welding condition on the maximum tensile force acting on a finishing end tack weld and to propose a suitable method to predict the maximum tensile force which is a primary factor of end cracking of butt-welding joints.A series of numerical calculations is performed based on unsteady heat conduction analysis and uncoupled elasto-plastic thermal stress analysis by use of the finite element method. Effect of mesh subdivision on accuracy of calculated results is carefully examined. It is suggested that use of a small time increment and a mesh size proportionate to weld heat input is necessary to acquire satisfactory results.An approximate formula to estimate the maximum tensile force acting on a finishing end tack weld is proposed. It is shown that the estimated values are fairly in good agreements with the calculated and/or measured values obtained hitherto, and that if we consider the optimum average width of fused zone for a welded joint with a given size, the maximum tensile force is specified only by welding speeds and becomes maximum for a specific welding speed.

End Cracking in Prestressed Members During Detensioning

This report is concerned with an investigation to determine analytically as well as experimentally the theory that end cracking observed during prestress transfer in pretensioned operations is caused by tensile stress induced by the restraining effect of relatively short length of unbonded cables. Production line prestressed members were monitored for strain increase during detensioning and the castings were measured for elastic shortening. Results were compared with an analytic model capable of furnishing cable strains during any detensioning scheme in a multiple casting operation. Full scale experimental members were designed such that during transfer tensile stress in concrete due to cable restraint would be maximized. Cracks were indeed caused as predicted by analytic calculations. Finally as an example problem, full scale production line girders were monitored for cable strain during detensioning and compared with analytically calculated values.

Studies on Prevention of End Cracking in One Side Automatic Welding (2nd Report)

Recently one sided automatic welding has widely been prevailed in the assemble stage of Japanese shipyards. As one of the problems of welding procedure, as well as any other welding techniques, cracking which sometimes occurs near the end of weld, has become an important problem.The authors have proposed the calculation technique in the seam welding. The most significant feature of the method differing from the ordinary welding thermal stress analysis is that the conditions of calculation are simulated to be those of more realistic welding procedures.Then, the following assumptions are imposed in order to calculate stress and strain during welding.(1) Before welding, specimens are connected by tack welds and prepared edges are free boundaries.(2) Molten region containing arc tip is free from stress.(3) After the arc passed by, the plates are connected by solidifying of the molten pool, that is, free prepared edge changes to supported one as temperature is cooled down.(4) When the arc passed through a tack weld, it should be melted away and free from stress.In order to calculate the thermal stress analysis during welding, firstly we solved un-stationary heat conduction problems and obtained temperature distribution during welding. Based on the calculated temperature distribution, we analysed uncoupled thermal stress problems by using the finite element method, and conclusively showed that one of the main causes of end cracking is the transient tensile stresses generated near the end part of weldment when the stress re-distribution is taken place due to the melting of the last tack weld.To endorse the numerical calculation by the proposed method, experiments are carried out and it is confirmed that the method could be applicable to this kind of transient welding stress-strain state with time depending varying boundary conditions.

Studies on Prevention of End Cracking in One Side Automatic Welding (3 rd Report)

Studies on Prevention of End Cracking in One Side Automatic Welding (3 rd Report)

Prevention of End Cracking in One Side Automatic Welding (1st Report)

The application of one side automatic welding has contributed to promotion of conveyor process for assembly stage of ship construction.In this process of one side automatic welding, however, it is observed that cracking appears in the center of weld metal mainly near the end of weld joints. To prevent this cracking, many experiments and investigations have been done from the viewpoint of dynamics and metallurgy and many useful methods have been developed and put into practice.Preventing method adopted in actual assembly stage is to restrain the opening displacement of the groove at end of weld joints by sealing bead. In this method, backing bead at end of weld joints is not always complete and has to be repaired.The authors confirmed formerly that end cracking in one side automatic welding occurred in relation between displacement and its rate at end of weld joints. In this paper, it is discussed on the improvement of deformation capacity of weld metal by changing of welding conditions on the basis of their fundamental experiments and it is clarified that the control of displacement and its rate at end of weld joints by means of special device gives vital effect on prevention of this end cracking.This preventing method was applied to actual weld joints in assembly stage. It was confirmed that this method was very useful.

片面自動溶接の終端割れに関する一考察

Some researchers have carried out, from a dynamics point of view, the investigations for various aspects of end cracking in one side automatic welding. Especially, the many studies with respect to the relation of rotational distortion and end cracking have been done heartily, since this, end cracking is found to be a kind of hot cracking induced above 1, 200°C. So it is comfirmed that the opening displacement of groove in the vicinity of plate edge is important factor for end cracking.In this paper, the authors give tensile load intentionally to the weld metal during solidification process on the assumption that the tack weld is melted and the groove is rapidly expanded, and discuss the effect of opening displacement and displacement rate on the end cracking behavior, from the viewpoint of the hypothesis of rotational distortion.