Ultimate Strength Behavior Research Articles

Semi-analytical simulation of plastic collapse mechanism of cracked continuous unstiffened plates used in ship structure under in-plane longitudinal compression

The present study is undertaken based on a nonlinear finite element study carried out by the same authors for estimation of ultimate strength of cracked continuous unstiffened plates used in ship structures under in-plane longitudinal compression. Investigations show that in addition to the magnitude of ultimate strength, the deflection shape and plastic collapse mechanism will also change completely. Results show that deflection in the cracked half wave increases more rapidly than other half waves. Consequently generated half waves in a cracked plate will not have identical length and amplitude. This implies that the conventional plastic collapse mechanism cannot be used to predict the behavior of cracked plates in the post ultimate strength region. A new plastic collapse mechanism based on the FEM results is suggested and the principle of virtual work is used to derive the axial stress-deflection relation of the plate. However, due to inequality of the length and amplitude of generated half waves, the axial stress-deflection relation cannot be directly derived from the principle of virtual work. Therefore, in order to solve the virtual work equation, some auxiliary relations between the involved parameters are required. Auxiliary equations are derived using regression analysis based on FEM results. Finally, a semi-analytical formulation is derived to estimate post ultimate strength behavior of cracked plates. It is shown that the proposed semi-analytical formulation can predict both magnitude and slope of the stress-deflection curves with better accuracy compared to the conventional plastic collapse mechanism. The formulation can be used within the defined ranges of simulated crack lengths, slenderness and aspect ratios.

Mechanical and Fatigue Properties of Gravity Die-Cast A356 Aluminium Alloy with Addition of Scandium

A356 is widely used for the casting of high strength components in automotive, aerospace and other industrial applications. This is due to its high achievable strength, castability, light weight, good thermal and electrical conductivity. However, the as-cast A356 exhibits relative poor mechanical properties due to the presence of coarse acicular eutectic silicon morphology. In this study, Sc-modified-A356 and the effect of heat treatment have been studied and compared with unmodified A356. Various amounts of Sc ranging from 0.2 wt% to 0.6 wt% were added into the mixture of A356 aluminium alloy and the specimens were produced by using gravity die-casting. Next, the ultimate tensile strength, Vickers hardness and fatigue behaviour of the cast samples are examined. The results revealed that by adding 0.4 wt.% of Sc, the heat treated sample is able to achieve ultimate tensile strength of above 300 MPa and Vicker’s hardness of 118 HV. Furthermore, the fatigue properties of the 0.4 wt% Sc-A356 with T6 heat treatment was found to be improved as compared to the unmodified A365 samples.

Testing and Numerical Modelling of Steel-Concrete-Steel with Stud Bolts Connectors Subject to Push-Out Loading

Steel-concrete-steel (SCS) sandwich panels are composed of two steel plates with low thicknesses and high densities and strengths and one thick layer between both plates with low strength and density known as core that is composed of concrete. Cohesive material-epoxy resin or shear connectors are usually applied in order to connect the plates to the concrete core. SCS sandwich composites are being developed so they can be utilized in offshore structures and buildings. Stud bolt is one of the shear connectors and their interlayer shear behavior is examined in the present study. In order to inspect the effect of parameters on interlayer shear behavior of steel-concrete-steel sandwich structure with stud bolt connectors, push-out test is performed under progressive loading. Pursuant to the tests performed, relations are proposed to predict ultimate shear strength and load-slip behavior of samples with stud bolt shear connectors. Consequently, numerical model of push-out test is presented on the basic component of Steel-Concrete-Steel sandwich structure (SCS) with stud bolt connectors. The results indicated that finite element model is consistent with test results applying mass scaling in Explicit Solver with a suitable analysis speed. Applying the regression analysis on the results of 80 numerical models of push-out test,a relation was proposed for shear strength of push-out samples with stud bolt connectors.

Mechanical Property and Damage Evolution of Polymer-Bonded eXplosive Substitute Under Biaxial Compression

Understanding both the mechanical property and the crack propagation behavior of Polymer-bonded eXplosive (PBX) material under biaxial compression is critical to predicting its safe working life. In this study, a number of PBX substitute specimens were tested under lateral confining pressures varying from 0 to 40[Formula: see text]MPa to better understand the mechanical behavior and damage evolution characteristics of PBX material under biaxial compression. The failure modes, ultimate strength and deformational behavior of PBX substitute under biaxial compression were observed using digital image correlation (DIC) method, and the damage of material was evaluated through the quantitative analysis of micro-computed tomography (CT) images of post-test specimens. The results indicate that the confining stress in the biaxial minor principal direction has a noticeable effect on the strength and deformational behavior of the PBX substitute material and the maximum increase of compressive strength occurs at a lateral confining pressure around 30[Formula: see text]MPa. The three-dimensional morphology of cracks was also examined quantitatively. The extent and complexity of crack damage were found increasing with the lateral confining pressure when it is smaller than 30[Formula: see text]MPa.

Effect of ECAP Die Angles on Microstructure Mechanical Properties and Corrosion Behavior of AZ80 Mg Alloy

In this article, the effect of channel angles on material properties was investigated during equal channel angular pressing of AZ80 magnesium alloy using processing route R at 325 °C processing temperature. Channel angles of 90° and 110° and common corner angle 30° have been considered for this study. It has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behavior of Mg alloys. Investigation with reference to as-received AZ80 Mg alloy indicates 18.47% improvement in UTS and 76.07% enhancement in ductility after processing through 3P-90° and 2P-110° ECAP, respectively. Also, the corrosion rate reduces to 89.47% after processing the sample with 3P-110° ECAP die.

Finite element modelling to predict the flexural behaviour of ultra-high performance concrete members

This paper presents a finite element (FE) modelling to predict the behaviour of ultra-high performance concrete (UHPC) members under static flexural loading. A plasticity-based constitutive model for concrete and an implicit solver in LS-DYNA were adopted in the numerical simulation. Experimental data for 21 UHPC specimens tested in the present study and in previous works were used to calibrate and validate the proposed FE model and modelling technique. The simulation was able to accurately predict the experimentally obtained ultimate strength, stiffness, and hardening and softening behaviours of the specimens. This demonstrates the effectiveness and adequacy of the developed FE model and modelling technique.

Experimental study on curved steel-concrete-steel sandwich shells under concentrated load by a hemi-spherical head

Steel-concrete-steel (SCS) sandwich shells, which are combined with steel plates, concrete core and shear connectors, are usually applied as protective structures in the civil engineering. In this paper, nine curved SCS sandwich shells subjected to concentrated load by a hemi-spherical head were tested to obtain the failure characteristic, ultimate strength and load–displacement response. The finite element (FE) models of curved SCS sandwich shells were also established by using LS-DYNA. The accuracies of the FE models were verified by comparing the load–displacement curves, local and global deformation between the experimental results and FE predictions. The factors influencing the ultimate strength and deformation behavior of curved SCS sandwich shells were analysed, including concrete core and steel plate thickness, top to bottom steel plate thickness ratio and spacing of shear connectors. Through experiments and numerical simulations, three failure modes could be summarized. It was also found that increasing concrete core and top steel plate thickness and reducing the spacing of shear connectors could increase yield strength and ultimate strength of curved SCS sandwich shell. The increase of concrete core and steel plate thickness also led to higher energy absorption capacity; whereas, the spacing of shear connectors showed little effect on energy absorption capacity.

Seismic behaviour of prestressed high-strength concrete piles under combined axial compression and cyclic horizontal loads

In order to simulate the seismic behaviour of the prestressed high-strength concrete piles under working state, six full-scale prestressed high-strength concrete piles were tested under combined axial compression and cyclic horizontal loads. Different axial compression levels and prestressing levels of prestressed tendons were studied in this test programme. The failure mode, bending resistance, displacement ductility, stiffness degradation and energy dissipation of the prestressed high-strength concrete piles under different loading scenarios were measured and analysed. Test results indicated that the axial compression ratio and prestressing level of prestressed tendon significantly influenced the seismic performance of prestressed high-strength concrete piles. Theoretical models were developed to predict cracking, yielding and ultimate bending resistances of the prestressed high-strength concrete pile under combined compression and bending. Finite element model was also developed to simulate the ultimate strength behaviour of the prestressed high-strength concrete pile under combined compression and flexural bending. The accuracies of the theoretical and finite element model were checked through validations of their predictions against the reported test results.

Ultimate strength of intact and dented steel stringer-stiffened cylinders under hydrostatic pressure

The aim of the study is to examine the effect of damages on the load carrying capacity of stringer-stiffened cylinders under external hydrostatic pressure. Experiments were conducted on three small-scale steel stringer-stiffened cylinder models that were fabricated by cold bending and arc welding. Drop tests with a knife-edge indenter were conducted on two test models to induce damage on the cylinders. Hydrostatic pressure tests of all models including an intact model were performed to characterize the ultimate strength behaviour of the stringer-stiffened cylinders in damaged and intact conditions. The results indicated that the effects of damage on the ultimate strength of stringer-stiffened cylinders were extremely low. Interestingly, during the collapse tests, it was also discovered that the shell failed several times after an initial failure, as evidenced by a sudden decrease in pressure. Subsequently, the shell recovered as “hardened-up” to reach a higher pressure level prior to the final collapse. Furthermore, the drop tests and hydrostatic pressure tests were simulated by using the finite element software package ABAQUS. The agreements between the tests and numerical predictions were satisfactory.

Ultimate Strength of Hull Plates under Monotonic and Cyclic Uniaxial Compression

As the most fundamental structural components of the ship hull, the hull plates' ultimate strength not only affects their own load bearing capacity, but also contributes to the ultimate strength of the whole ship hull. Through the literature survey of the ultimate strength of hull plates, it can be found that most of the ultimate strength research studies focused on the ultimate strength behavior of hull plates under monotonic increasing loading. Considering the motion and deformation of hull girders among sea waves, the ultimate bearing capacity research of the hull structures under cyclic loading maybe more in line with reality. In this article, the local instability tests of plates under cyclic uniaxial loading carried out by Fukumoto and Kusama is reanalyzed. Based on the tests carried out by Fukumoto and Kusama, some fundamental behaviors about the ultimate strength and unloading and reloading paths of the plates under cyclic uniaxial compression are summarized. Then, a simple approach to construct the average stress-average strain relationship of the hull plates exposed to cyclic compression is proposed. Finally, tests on six square-column models are carried out to simulate the collapse behavior of the hull plates under cyclic uniaxial compression. The present study shows that the average stress-average strain relationship of hull plates under cyclic compression can be constructed by a simple approach conveniently and accurately. Meanwhile, the ultimate strength behavior of the hull plates under cyclic uniaxial compression can also be reflected well by the simple approach. 1. Introduction Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. An appropriate level of the ultimate strength of a ship hull is perhaps its most important guarantee of structural safety. Accurate assessment of the ultimate strength and/or residual ultimate strength of a ship is pertinent not only for the initial design, but also for the operation, maintenance, repair, and even disaster management, rescue, and salvage assessment of the ship hulls in accident situations. The first attempt to calculate the ultimate hull girder strength was developed by Caldwell (1965), who applied "Rigid Plastic Mechanism Analysis" to evaluate the ultimate strength of the hull girder. From then on, the ultimate strength of ship structures (including plates, stiffened plates, and hull girders) was widely studied by numerous scholars. Certainly, a great deal of developments have made naval architects obtain a clearer understanding of the ultimate strength behaviors of ship structures. However, because of the complexity and importance of the problems related to the ultimate strength, they still need to be explored more deeply. As described in the report of 19th International Ship and Offshore Structures Congress (ISSC 2015), "with these developments ultimate strength assessment is now becoming a more important issue to ensure the safety of ship structures."

절곡강판을 적용한 강박스거더 압축플랜지의 탄성좌굴 및 극한 거동

절곡강판을 적용한 강박스거더 압축플랜지의 탄성좌굴 및 극한 거동

Ultimate strength behaviour of S-UHPC-S and SCS sandwich beams under shear loads

The application of steel-concrete-steel (SCS) sandwich structures as containment buildings is proposed for the third-generation nuclear power plant AP1000. In this paper, ultra high-performance concrete (UHPC) is developed as the core material to improve structural behaviour. Static tests on two groups of SCS sandwich beams and two groups of steel-ultra high- performance concrete-steel (S-UHPC-S) sandwich beams were carried out to investigate the structural behaviours under three-point loading, with the research parameters consisting of the shear reinforcement ratio and core materials. Three failure modes are defined and the structural behaviours are analysed, considering the effects of the shear reinforcement ratio, shear studs and core materials on the specimens. Based on the test results, mechanical models are established to predict the shear bearing capacity of SCS sandwich beams, taking into consideration the effect of the contribution of the steel plates and the bond-slip action between the steel plates and concrete. Furthermore, a calculation method for predicting the ultimate strength of S-UHPC-S sandwich beams is presented, which takes into account the effects of steel fibres on specimens. The prediction accuracy is verified by means of comparison with the test data.

Ultimate Strength Assessment of Hull Girder under Cyclic Bending Based on Smith’s Method

Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. Accurate assessment of the (residual) ultimate strength of a ship hull is important not only for the initial design, but also for the operation, maintenance, repair, and even for disaster management, rescue, and salvage assessment of the ship hulls. In fact, under ocean wave conditions, the hull girder is likely to withstand extreme cyclic bending. In this article, a simplified method based on Smith's method is proposed to assess the ultimate strength of the ship hulls under extreme cyclic bending. To obtain the nonlinear average stress-average strain relationship (σ-ε curve) of the basic structural element (consisting of a stiffener with its attaching plating) under cyclic in-plane compression and tension, systematic calculations are carried out by using a combination of the Beam-Column analysis and the nonlinear finite element method (NLFEM). By introducing the cyclic σ-ε curves of basic structural elements to a simplified calculation program, which is developed by the authors and based on Smith's method, the ultimate strength of hull girders exposed to extreme cyclic bending is subsequently determined. The ultimate strength of three box girder models and an actual ship are obtained under cyclic bending by using the authors' developed procedures including the simplified calculation program and are compared with the corresponding results from NLFEM calculations and also the box girder experiments. 1. Introduction Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. An appropriate level of the ultimate strength of a ship hull is perhaps its most important guarantee of structural safety. Accurate assessment of the ultimate strength and/ or residual ultimate strength of a ship is pertinent not only for the initial design, but also for the operation, maintenance, repair, and even for disaster management, rescue, and salvage assessment of the ship hulls in accidental situations. Perhaps the first attempt to calculate ship hull girder ultimate strength was by Caldwell (1965), who applied a type of rigid plastic mechanism analysis to evaluate strength. Since then, naval architects have gradually realized various technology developments and advances of importance to the ultimate strength assessment of ship structures. Over the last two decades, the ultimate bearing capacity of ship structures (including plates, stiffened plates, and hull girders) in their many different modes of possible behavior has been widely studied, and a great deal of results developed, which have made possible an increasingly clearer understanding of the ultimate strength behavior of ship structures. However, because of the complexity and importance of the problem, and the need for continuing development is still felt, for example, as described in the 19th International Ship and Offshore Structures Congress (ISSC) report, which emphasizes that (even) "with these developments ultimate strength assessment is now becoming a more important issue to ensure the safety of ship structures."

Post-Buckling Behaviour and Buckling Strength of the Circular Cylinder Under Axial Compression

Cylindrical shells are often used in the construction of ship and land-based structures such as deck plating with a camber, side shell plating for fore and aft part pipes, as well as storage tanks. It has been believed that such curved shells can be modeled fundamentally as a part of the cylinder under axial compression. From the estimations made based on cylindrical models, it is known that in general, curvature increases the buckling strength of a curved shell when subjected to axial compression, and the same curvature is also expected to increase the overall strength. A series of elastic large deflection analyses were conducted in order to clarify the fundamentals observed in the buckling and post-buckling behaviour of circular cylinders under axial compression. In the present paper, an FE-series analysis has been performed based on the elastic large deflection behaviour, and the effect of parameters has been clarified. The ultimate strength behavior of the circular cylinder was found to be significantly influenced by both the initial deflection and the FE-modeling method.

Developments and mechanical behaviors of steel fiber reinforced ultra-lightweight cement composite with different densities

Ultra-lightweight cement composite (ULCC) has attracted extensive research interests in both civil and offshore engineering constructions due to its high specific strengths. In order to satisfy different engineering construction demands, four types novel steel fiber reinforced ultra-lightweight cement composite (ULCC) with different densities ranging from 1250 kg/m3 to 1550 kg/m3 were proposed. Extensive standard compressive and tensile tests were performed to obtain the mechanical properties of these ULCCs with different densities, which will offer useful information for the developments of design on engineering constructions with such types of ULCC. Based on these test results, constitutive laws were established to describe the compressive and tensile stress–strain behaviors of ULCC with varying densities. Regarding the applications of the ULCC in engineering constructions, a ULCC flat slab with density of 1550 kg/m3 under concentrated loading was tested. The failure mechanisms and ultimate strength behaviors of this ULCC flat slab were reported. 3D FE model was also developed to simulate the structural behaviors of the novel ULCC flat slab, and its accuracy was confirmed by the reported test results. With the validated FE model and reported mechanical properties of ULCC with different densities, structural behaviors of ULCC flat slabs with these ULCCs were investigated. Analytical model based on the method of bending resistance in MCS-EPFL was proposed to predict the ultimate resistance of ULCC flat slab.

Mechanical Properties and Wear Behavior of AA5182/WC Nanocomposite Fabricated by Friction Stir Welding at Different Tool Traverse Speeds

Grain growth inhibition at the heat-affected zone, improved weld strength and superior tribological properties of welds are desirable attributes of modern manufacturing. With the focused on these attributes, tungsten carbide (WC) nanoparticles were employed as reinforcements for the friction stir welding of 5-mm-thick AA5182 aluminum alloy by varying tool traverse speeds. The microstructure, microhardness, ultimate tensile strength, fracture and wear behavior of the resultant WC-reinforced welds were investigated, while unreinforced AA5182 welds were employed as controls for the study. The result shows that the addition of WC nanoparticles causes substantial grain refinement within the weld nugget. A decrease in traverse speed caused additional particle fragmentation, improved hardness value and enhanced weld strength in the reinforced welds. Improved wear rate and friction coefficient of welds were attained at a reduced traverse speed of 100 mm/min in the WC-reinforced welds. This improvement is attributed to the effects of reduced grain size/grain fragmentation and homogeneous dispersion of WC nanoparticles within the WC-reinforced weld nugget.

Investigation on Mechanical Behavior of I-Section Steel Columns After Elevated Temperature

This paper presents the experimental and numerical investigations on mechanical behavior of I-section steel columns after elevated temperature exposure. A total of twenty-six compression tests were carried out, in which one was under ambient temperature and the other twenty-five were under heating and cooling phase to study the influence of high temperature (400, 550, 700, 850, 1000°C) and high temperature duration (0.5, 1, 1.5, 2, 2.5 h) on mechanical behavior of the specimens. The failure pattern, axial load versus strain relation, axial load versus displacement relation and ultimate strength of the specimens were presented and analyzed. The test results showed that, high temperature duration had limited influence on the ultimate strength and other mechanical behaviors of the specimens, while the ultimate strength decreases with the increase of the maximum temperature the specimens suffered and some other behaviors also changed. The failure pattern of specimens after high temperature did not change compared with that of specimens under ambient temperature. The finite element models that have the same geometry with the test specimens were set up to compare with the test specimens and the results predicted from finite element analysis showed good agreement with that measured in test. Therefore, parametric study was carried out to investigate the influence of different section geometry on the ultimate strength of I-section steel short columns after elevated temperature. A new relationship for the ultimate strength for I-section steel short columns after elevated temperature was developed and proved to be reliable and accurate. What’s more, the effect of slenderness ratio on the stability coefficient of the columns was also investigated in the parametric study.

Analytical and numerical studies on steel columns with novel connections in modular construction

Prefabricated modular construction is a new type of promising structures. This type of structure is an excellent alternative to conventional on-site buildings with advantages of shortened construction time, improved construction quality and reduced environmental pollution. A new concept of modular construction with novel connections has been proposed. This paper mainly focuses on the behavior and design of the innovative steel column working together with tenons at both ends. The fourth-differential equation was firstly adopted to develop a theoretical model to determine the buckling length of the column. Then, a 3-D nonlinear finite element (FE) model was developed to simulate the ultimate strength behavior of the novel column under pure compression. Parametric studies reveal that the tenons play a significant role in affecting the ultimate load and the corresponding end shortening, among which the length of the tenons is the most important factor. The design approach and recommendations are also discussed through assessing the applicability of the current design code.

A damage model based on the introduction of a crack direction parameter for FRP composites under quasi-static load

Continuum damage mechanics model with consideration of crack direction is developed for the prediction of fracture behavior in fiber reinforced polymer (FRP) composites under quasi-static load. Traditional continuum damage mechanics (CDM) models cannot well predict the crack propagation path in the development state of discrete crack. The crack direction parameter is introduced as a major factor with damage variable for damage propagation and failure analysis. The CDM model, which has the capability to reliably predict the initiation and direction of crack propagation while analysing the multi failure of FRP composites, is proposed by introducing crack direction parameter to material property degradation method. Failure criteria is set up according to the behavior of FRP composites for damage initiation, and fracture-mechanics-based energy release rate criteria is employed for damage evolution. APDL is used to simulate crack propagation, ultimate strength and complex failure behavior of FRP composite structure for this model. Results from the previous researches, when compared with those of this model, showed good agreement, thus demonstrating that proposed methodology can be used for simulation of FRP composite damage failure and strength prediction.

Numerical analysis on steel-concrete-steel sandwich plates by damage plasticity model: From materials to structures

Steel-concrete-steel (SCS) sandwich type of ice-resistant wall has been developed for arctic offshore structures. This paper develops a three-dimensional damage plasticity based finite element model (FEM) to simulate the ultimate strength behaviour of SCS sandwich structure under concentrated loads. The FEM offered detailed simulations on the complex geometry of hundreds of studs, complex interactions of these connectors with the concrete, and mechanical nonlinearities of the steel and concrete materials. Concrete damage plasticity model was used to simulate the post-peak softening of concrete, and continuum damage model (CDM) was developed to phenomenologically simulate the damage evolution in the steel materials. The key parameters in the CDM were calibrated by the uniaxial tensile tests on the steel coupons. The accuracy of the FE simulation was checked by nine full scale tests. The validations proved that the developed FEM simulate well the ultimate strength behaviours of the SCS sandwich plates under concentrated loads in terms of load-deflection curves, ultimate resistances, and failure modes in the steel plates, studs and concrete core. Through the FE simulations, the failure modes corresponding to different peak resistances were analysed and recognized. Finally, the FE simulation procedures on SCS sandwich plate with CDM and CDPM were recommended.