Cruciform Type Research Articles

Fracture prediction in transverse fillet welded joints of high strength structural steel

Due to the huge property difference between high strength structural (HSS) steels and mild steels after welding, mechanical behavior and failure mode of fillet welded joints of HSS steels should be studied further. Numerical simulations can provide increased insight into this topic. This paper concerns finite element simulations of component tests of two types transverse fillet welded joints of HSS steels: lap-welded transverse fillet welds and cruciform type transverse fillet welds. In order to investigate the influences of triaxial stress states on fracture ductility of weld metals, a series of tests on specimens with various initial geometries are carried out. By comparing three typical uncoupled fracture models (stress triaxiality-dependent ductile fracture model (VGM), Lode angle-dependent ductile fracture model (MSSM) and combination of stress triaxiality and Lode angle ductile fracture model (BWM)), BWM gives precious prediction of ductile fracture of weld metals. The behaviors in terms of load-displacement and failure modes of transverse fillet welds are all well captured by the numerical simulations with calibrated ductile fracture models. Specifically, the location of fracture initiation and propagation of cracks obtained from simulations are both identical with real responses.

Mechanical behavior of transverse fillet welded joints of high strength steel using digital image correlation techniques

Mechanical behavior of 24 lap-welded fillet joints and 20 cruciform fillet joints made of high strength steels (HSS) under tension load is investigated by experimental study. Traditional deformation measurements for transverse fillet weld joints have many weaknesses, which can be solved by digital image correlation techniques (DIC). The strain distribution development over the specimen along the whole loading process were analyzed by using DIC measurement. Test specimens were prepared using four classifications of filler metal and two weld sizes were included in each type of transverse fillet welded specimens. The effect of parameters (e.g. weld size and mismatch ratio) on mechanical properties (e.g. failure modes, fracture angle, ultimate strength and weld ductility) of those two types transverse fillet weld were compared. Due to the softening and other metallurgical effects, cruciform type specimens are more prone to fail around fusion lines than weld metal. Generally, because of the existence of friction force, mean strength of lap-welded specimens are higher than that of cruciform type specimens. The mean ductility of lap-welded specimen is similar to that of cruciform type specimen. Two load-deformation curve features, “rise” feature and “platform” feature, were identified. Most lap-welded specimens have “rise” feature load-deformation curve while most cruciform type specimens have “platform” feature load-deformation curves. Generally, the specimens with “rise” feature load-deformation curve are more likely to suffer sudden fracture. The instantaneous and simultaneous fracture was observed at fracture surface of lap-welded specimen. Joint misalignment has significant impact on the deformation patterns of cruciform type specimens. Based on load-deformation curves of cruciform type specimens, three deformation patterns were proposed. Due to the existence of three deformation patterns, the variability of strength and ductility are much larger than lap-welded joints. Moreover, it is confirmed that EC3 and AISC Specification are conservative for all mismatched filler metals.

Determination of instability of a DP 980 steel sheet under different stress states based on experiment and theoretical models

It is generally accepted that the formability of sheet metal is limited by the onset of instability which can be described by forming limit diagram (FLD) in e 1 -e 2 space. Common tests for FLD data usually cover strain ratio range from uniaxial to equal biaxial stretching, −1/2 ≤ e 2 /e 1 ≤ 1. In this paper a new design of cruciform type specimen for uniaxial stretching is proposed to test formability with strain ratios in the range from shear to tension, −1 ≤ e 2 /e 1 ≤ −1/2 which can be controlled by the geometry parameters. The forming limit of a DP 980 steel sheet was determined using both conventional method and proposed specimen with strain ratios from −1 ≤ e 2 /e 1 ≤ 1. Then the experimental results were drawn in both e 1 − e 2 and e eq −σ m /σ eq spaces, and the predicted results based on Hill, Swift, M-K, and Hora instability models were compared with the experimental ones. The formability features of the studied steel in whole strain ratio range and differences among the investigated theoretical models were finally discussed. The results indicate that the M-K instability model shows better prediction of the studied steel compared to the other models investigated in this research.

Memorije križnoga tlocrta na tlu Istre i Dalmacije

Autor raspravlja o kršćanskim memorijama križnoga tlocrta nastalima u vremenu od kasne antike do romanike na tlu Istre i Dalmacije. Bavi se pitanjem trajanja forme i funkcije koju dobro ocrtava primjer tzv. mauzoleja Galle Placidije u Ravenni. Kompaktnu skupinu sličnih građevina čine bizantske memorije na jugu Istre, u Puli: krstionica, dvije kapele uz baziliku sv. Marije Formoze, te crkva sv. Mateja pred zidinama i Sv. Katarine na otočiću ispred Pule. Donekle su problematični oblik i vrijeme nastanka kapele sv. Andrije na otičiću ispred Rovinja. Srodne crkvice Sv. Klementa na Vrhu pred Pulom i sv. Tome nedaleko Rovinja upućuju na kontinuitet tog arhitektonskog tipa i tokom ranoga srednjeg vijeka u pulskoj regiji. Skupina sličnih građevina u Dalmaciji nema takvu kompaktnost. Krstionica u Baškoj na otoku Krku znatno je manja od crkve sv. Martina na Cresu, a jedna i druga različite su od trikonhalne nutrine u kapeli sv. Ciprijana u Gatima, te njene, vjerojatno nišama, raščlanjene vanjštine. S druge strane upravo su jednake dvije ranosrednjovjekovne kapele: sv. Vid u Zadru i sv. Križ u Ninu. One obnavljaju predloške ranokršćanskih križnih memorija. Indikativna je srodnost njihovih kupola s nekim primjerima iz bizantske arhitekture 10. i 11. stoljeća. Romanička kapela Sv. Dunata pored Kornića na otoku Krku ima neobično rješenje s oblim apsidama u poprečnoj osi prostora. Bogomolja nepoznatog titulara na Crkvini pored Kašića, nedaleko Zadra, srodna je drevnome tipu memorije s tri apside grupirane na začelnoj strani. Unatoć pojedinim razlikama ipak sve memorije i obje njihove skupine povezuje slična križna forma i funerarna funkcija te kontinuitet samog oblika i njegove namjene na tlu Istre i Dalmacije u vremenu od kasne antike do romanike. Zamjetan je također utjecaj bizantskih sredina na oblikovanje takvih memorija u kulturnom krajoliku Jadrana.

Design optimisation of biaxial tensile test specimen using finite element analysis

One of the most restricting aspects of the biaxial tensile test for sheet metal is the design of the cruciform specimen. Although specimens of the cruciform type have been investigated quite extensively previously, no standard geometry for the cruciform specimen exists. Using a specifically designed pantograph apparatus for operation in a standard tensile testing machine, various cruciform specimens machined from low-carbon cold rolled steel sheet were analysed experimentally. Finite element modelling of the specimens was conducted in parallel to the experimental test programme to establish optimum specimen geometry. Through a process of optimisation, a standard cruciform specimen was designed which can be used to accurately predict the mechanical behaviour of the mild steel when formed in multiple directions simultaneously. This paper describes the optimisation process and the results obtained from both the experimental testing and numerical modelling.

Optimisation of Cruciform Test Specimen for Biaxial Tensile Testing of Sheet Metal

One of the most restricting aspects of the biaxial tensile test for sheet metal is the design of the cruciform specimen. Although specimens of the cruciform type have previoussly been investigated quite extensively, no standard geometry for the cruciform specimen exists. Using a specifically designed pantograph apparatus for operation in a standard tensile testing machine, various cruciform specimens were analysed experimentally. Finite element modelling of the specimens was also conducted to establish optimum specimen geometry. Through a process of optimisation, a standard cruciform specimen was designed which can be used to accurately predict the mechanical behaviour of cold rolled low-carbon steel when formed in multiple directions simultaneously.

An investigation of the mechanical behavior of carbon epoxy cross ply cruciform specimens under biaxial loading

AbstractIn this study, carbon epoxy cruciform type specimens with a cross‐ply layup were biaxially and uniaxially in‐plane loaded using four independent servo‐hydraulic actuators. Four different biaxial loading ratios were investigated when the applied load was quasi‐static. A comparison between experimental observations (for the damage and strain evolution of the biaxially loaded central section of the specimen) coming from digital image correlation measurements and a 3D finite element damage model will be shown. The symmetry and the uniformity of the strain field on the biaxially loaded zone were by the use of digital image correlation measurements investigated. Furthermore, the failure loads coming from the load cells of the machine were straightforward compared with the output of the finite element damage model. POLYM. COMPOS., 31:1554–1561, 2010. © 2009 Society of Plastics Engineers

Shape optimisation of a biaxially loaded cruciform specimen

In the present study, the shape of a cruciform type specimen under biaxial loading conditions is optimised. The basic goal is to achieve uniform biaxial failure in the centre of the specimen and minimise undesirable phenomena, such as premature failure outside the area of interest and non uniformities on the central strain field, caused by stress concentrations. A numerical optimisation technique (sequential quadratic programming or SQP) is coupled with a parametrically built finite element model (FEM) to concentrate and initiate damage in the centre and achieve a uniform strain field by varying the geometrical characteristics of the specimen. The outputs of the optimisation process are compared with a commonly used cruciform type geometry.

Biaxial testing of fibre-reinforced composite laminates

Advanced composite material systems are increasingly used in almost every industrial branch. The structural components manufactured from these composite material systems are usually subjected to complex loading that leads to multi-axial stress and strain fields at critical surface locations. The current practice of using solely uniaxial test data to validate proposed material models is wholly inadequate. In order to test closer to reality, a biaxial test bench using four servo-hydraulic actuators with four load cells was developed. Besides the development of the test facility, a mixed numerical/experimental method was developed to determine the in-plane stiffness parameters from testing a single cruciform test specimen. To obtain the strength data an optimized geometry for the cruciform type specimen was designed. For the optimization procedure a full three-dimensional finite element model was used. The numerical results were validated with strain gauge, digital image correlation, and electronic speckle pattern interferometry data. The material system used for the experimental validation was glass fibre-reinforced epoxy with a lay-up [(+45°−45° 0°)4(+45°−45°)] typically used for wind turbine blades.

Behavior and strength of steel reinforced concrete beam–column joints with two-side force inputs

Experimental results from five large-scale cruciform type beam–column subassemblies showed that: (1) the SRC joint demonstrated a more moderate pinching phenomenon than the RC joint; (2) the shear strength provided by the longitudinal flanges of the cross-H steel section was significantly higher than expected; (3) the definition of the joint zone of the SRC column-wide flange beam system should be modified to match experimental observations; and (4) the corner ties can be used to replace joint hoops without demonstrating any negative behavior. It was also found that the strength superposition method was able to predict the SRC joint shear strength with reasonable accuracy.

Design of a cruciform specimen for biaxial testing of fibre reinforced composite laminates

To study the behaviour of fibre reinforced composite laminates under static and cyclic in-plane complex stress states, a biaxial loading frame has been developed. A cruciform type specimen is biaxially loaded in its plane using four independent servo-hydraulic actuators. An appropriate control unit keeps the centre of the specimen at the same position during the test. For obtaining reliable biaxial failure data the design of the cruciform specimen is of paramount importance. Finite element simulations of the cruciform specimen to study the influence of various geometrical parameters and experiments on nine selected cruciform specimen types using both strain gages and an optical-numerical full field method for strain determination over the entire biaxially loaded test zone have been carried out. In the present paper, the four most important geometries will be discussed. Since stresses in the biaxially loaded zone cannot be calculated from the experimentally applied loads due to the ill definition of the load bearing area, strain values – the only measurable quantity – are used for the comparison of the different geometry types. For the glass fibre reinforced composite material with a [(±45/0) 4/±45] T lay-up this led to the proposal of an optimized geometry: a plane cruciform type specimen with a circular central region of reduced thickness and an adapted corner fillet at the intersection of the arms. Using this geometry failure will occur in the biaxially loaded test zone, rather than in the uniaxially loaded arms, at failure strains in the centre of the specimen comparable for the uniaxial load ratios to strains obtained on standard beam specimens. Tests at different load ratios were performed to obtain data as input for failure criteria. This paper focuses on the design of the specimen. In the near future, the biaxial test results will be compared with existing failure criteria.

Forecasting construction durations for public housing projects: a Hong Kong perspective

The past thirty years have seen a great surge of international attention and discussion in the domain of construction time performance of building projects. Demand for residential construction has been continually increasing in Hong Kong since the 1950s, while an accelerated demand has been envisaged in the next few years up to 2001. This paper is based on the findings of the third survey in an investigation which aimed at determining a group of critical factors that affect construction durations of building projects in Hong Kong. This stage of the study attempted to generate standards (norms) for overall completion periods of public housing blocks, by modelling the durations of the primary work packages in the building construction process, i.e. piling, pile caps/raft, superstructure, EandM services, finishes and their respective sequential start-start lag times, in terms of the identified sets of critical factors (significant variables). Data from 15 case studies of standard New Cruciform type housing blocks was collected from the client and contractors. Multiple Linear Regression was applied in analyzing the project data and formulating a construction duration model. The forecasting performance of the model was next evaluated using an independent (new) set of project information from the client, in terms of a relative measure known as the Percentage Error. Both the general applications and drawbacks of the model are briefly presented and examined herein. The low values of percentage error (less than about ±10%) for overall construction durations confirmed that the model can be a reliable tool for predicting the construction durations of public housing projects in Hong Kong; and the research methodology used could well be extended to similar studies and duration forecasts in other sub-sectors in Hong Kong, as well as in other countries.

Fracture of steel beam to box column connections

Abstract This study is aimed at examining the behavior of the beam to interior box column connection. Cruciform type test setups are selected with the column under constant gravity load while both beams under gradually increased cyclic loading in opposite directions to simulate earthquake load. The tearing strength of the column plate by the transmitted out‐of‐plane load from the beam web is analyzed by yield line theory. A simplified method is proposed to establish the relationship between the thickness of beam web and column plate. A series of experimental studies are also conducted to examine the effect of a diaphragm plate on the transmission of applied force from beam flanges. Based on the results of this study, suggestions are made for the design and construction of beam to box column connections to achieve better strength and ductility.

Stabilimenta characteristics of the spider Argiope argentata on small islands: support of the predator-defense hypothesis

A variety of orb-weaving spider species construct stabilimenta, patterned areas of dense silk, typically near the hub of the orb. The adaptive significance of this construction, along with associated behaviors such as shuttling and vibrating, is much debated. Arigiope argentata on small islands of the Bahamas frequently possess stabilimenta; we studied 397 individuals of this species to investigate possible functions of their stabilimenta, paying particular attention to predator-defense hypotheses. Cruciform stabilimenta were commoner in all size classes of spiders than discoid stabilimenta or no stabilimentum at all; discoid stabilimenta occurred mostly among intermediate size classes. Within the cruciform type, two-segmented stabilimenta were especially common among the very smallest spiders. Size of cruciform stabilimenta showed a curvilinear relation to spider body length; the fitted curve for “total segment length” had a maximum at an intermediate spider length. We argue that this relationship (among other phenomena) supports an apparently-larger-size hypothesis, whereby intermediate-sized spiders in particular appear much larger than they actually are. This could discourage predators, including those that are gape-limited such as lizards. We argue that stabilimenta in the smallest spiders, in which typically two segments are opposed, so that they more or less “line up”, serve as camouflage. When disturbed experimentally, spiders with discoid stabilimenta shuttle to the opposite side of the centrally located stabilimentum. This seems an obvious defensive behavior and occurs less frequently among spiders with cruciform stabilimenta. Large spiders vibrate more frequently than small ones, but no relation exists between vibration frequency and stabilimentum type. We argue (see also Tolbert 1975) that vibrating behavior, in which the spider can become a blur, renders its location more difficult to discern and the spider more difficult to grasp, rather than increasing apparent size.

角形鋼管柱の左右にせいの異なる梁が接合される場合の梁の剛性と耐力に関する研究

At the connection of H-shaped beams and RHS-column as shown in Fig. 2, stiffness and moment capacity of smaller depth beam are govered by rigidity of column flange. In this paper, analytical study for predicting elastic stiffness and moment capacity of beam mentioned above and experimental results are reported. The elastic stiffness of beam was derived by assumig the column flange would behave as grid beams. For the moment capacity, the theoretical expression was developed based on the yield line theory. And to confirm the precision, the analytical results were compared with the experimental results obtained from 14 simple beam type specimens under monotonic loading and 5 cruciform type specimens of beam-to-column sub-assemblage under cyclic loading. In those tests, the parameters of specimens were thickness of RHS-column, disparity between lower beam flange and diaphragm, and width of beam-flange. The analytical results were closely coinside with the corresponding test results.

A FRACTURE MECHANICS APPROACH TO HIGH-CYCLE FATIGUE CRACK GROWTH UNDER IN-PLANE BIAXIAL LOADS

Abstract Fatigue crack growth under biaxial tensile load conditions is reported for a structural sheet steel. The new test facility can operate at high frequency (0–40 Hz) thereby permitting real-time testing required for threshold investigations; specimens are of the cruciform type. It is found that crack growth rate is affected by a cyclic tensile load applied in the direction of growth which decreases as the said load increases. The rate however increases if the biaxial loads are increasingly out of phase. Within the test conditions reported LEFM can be applied to crack growth under biaxial load conditions. The threshold stress intensity range is shown to be a function of load biaxiality, phase difference and stress ratio.

ホーミングを行なう飛しょう体の運動解析

The motion of homing-missile in case of threedimensional space is analyzed, and effect of spinning of missile which is inevitable in cruciform type missile and have large effect on missile's homing characteristic is investigated. In analyzing this problem, we assume that missile has constant spin velocity and has devices to execute proportional navigation. Spinning of missile, combined with responce lag time of guidance and control system cause to missile's complicated motion. In this paper characteristic of guidance and control system is represented by double, first order linear system

Gametogenesis and Embryogeny of Tamarix ericoides Rottl1

The haploid chromosome number in Tamarix ericoides Rottl., reported for the first time, is twelve.The archesporial cell is single, rarely double.There is no tetrad formation, division of the megaspore mother-cell; instead, a four nucleate embryo-sac results.The nuclei are originally arranged in a cruciform type, but later form a I+3 arrangement.As a result of the third division, the embryo-sac is again four-nucleate, with two haploid nuclei at the micropylar end and two triploid nuclei at the chalazal end.The cells of the embryo-sac are formed at the end of the fourth division, the embryo-sac thus representing the sixteen nucleate condition.The development of the embryo-sac of Tamarix ericoides conforms to the Fritillaria-type.The endosperm is free nuclear, and the embryo is characteristic in developing a massive suspensor and a large pad of cellular tissue from the proximal cell.Double embryo-sacs and the occurrence of polyembryony are reported for the first time in the family.

The Effect of Form on the Reverberation of Sound in Rooms

Measurements of the mean free path p of sound in three dimensional models of eleven typical auditoriums—such as rectangular rooms (with and without balconies), fan shaped theatres, country and city churches, and rooms with gabled, barreled or domed ceilings—indicate that p varies from about 3.8 V/S (V=volume, S=interior surface) in a large rectangular room with a low ceiling to 4.3 V/S in a cruciform type of church auditorium. The reverberation formula for the impressed vibrations takes the form t=kV−rS loge (1−α)+4mV where k depends upon the shape of the room and has a value of .046 in the large room with the low ceiling, .053 in the cruciform type of church auditorium, and about .049 for the conventional type of room; r is a probability factor which depends upon the location of the absorptive material in a room; and m is the attenuation constant of the air. The more exact theory of reverberation must describe also the rate of decay of the free vibrations in a room. Some measurements of reverberation have been made in a small room which exhibit gross violations of the generally accepted reverberation formula. These measurements reveal the necessity of considering the free vibrations in reverberation theory.