Loss Of Load-carrying Capacity Research Articles

Efficient bonding of ethylene-propylene-diene M-class rubber to stainless steel using polymer brushes as a nanoscale adhesive

A novel approach to bond rubber to metal using nanometers thick polymer brushes in the interface is investigated. An atom transfer radical polymerization (ATRP) initiator is grafted to the surface of stainless steel (SS) and poly(glycidyl methacrylate) (PGMA) brushes are grown from the surface. Benzoyl peroxide (BPO) is drop casted on the polymer films before the samples are overmolded with ethylene-propylene-diene M-class (EPDM) rubber. For surface concentrations below 0.2 µmol cm-2 regions with adhesive failure were observed. Thermal infrared reflectance absorption spectroscopy (T-IRRAS) and X-ray photoelectron spectroscopy (XPS) show a conversion of oxirane groups after heating samples to 170 °C.A compression molding system designed to mold uncured rubber on modified SS samples and subsequently to perform peel tests of the rubber-steel specimens are presented. Four stages of crack propagation are identified in the peel data: 1) elastic loading, 2) stable crack propagation, 3) unstable crack propagation, and 4) loss of load carrying capacity. The novel nanometer thick bonding system was benchmarked against a commercial bonding system. Calculated peel energies are in good agreement with previously reported values and show no significant difference compared to a commercial bonding agent. Therefore, it is concluded that the novel bonding system applying only a nanometer thick surface immobilized polymer brush layer offers similar adhesion as existing micrometer thick primer adhesives.

Damage characterization in a ferritic steel sheet: Experimental tests, parameter identification and numerical modeling

The Gurson–Tvergaard–Needleman (GTN) model includes several parameters of different nature. Some of them have micromechanical roots while others are strictly phenomenological. Hence, a methodology should be developed in order to obtain a robust set of parameters with both numerical and physical meaning. The material parameters of the GTN model are found using an identification methodology based on experimental-numerical results. The method is applied on a DC01 ferritic steel sheet. An extended version of the Gurson model, incorporating plastic anisotropy, mixed isotropic-kinematic hardening, void nucleation, growth, coalescence and shear is used. Material parameters are obtained based on an inverse optimization and a sensitivity analysis on specimens with different geometries. The onset of coalescence, reflected as the loss of load carrying capacity in the force-displacement curve, is correctly predicted by the extended GTN model. The strain distribution, obtained by digital image correlation, is also correctly simulated. Nevertheless, the model does not to predict the increase of strain observed experimentally, because of the decoupling between hardening and the damage variable. In this respect, the article provides experimental evidence of the limitations of a GTN model based on a strain-controlled nucleation law with heuristic extensions of hardening.

Mechanical robustness of AREVA NP's GAIA fuel design under seismic and LOCA excitations

Abstract Recent events in the nuclear industry have resulted in a movement towards increased seismic and LOCA excitations and requirements that challenge current fuel designs. AREVA NP's GAIA fuel design introduces unique and robust characteristics to resist the effects of seismic and LOCA excitations. For demanding seismic and LOCA scenarios, fuel assembly spacer grids can undergo plastic deformations. These plastic deformations must not prohibit the complete insertion of the control rod assemblies and the cooling of the fuel rods after the accident. The specific structure of the GAIA spacer grid produces a unique and stable compressive deformation mode which maintains the regular array of the fuel rods and guide tubes. The stability of the spacer grid allows it to absorb a significant amount of energy without a loss of load-carrying capacity. The GAIA-specific grid behavior is in contrast to the typical spacer grid, which is characterized by a buckling instability. The increased mechanical robustness of the GAIA spacer grid is advantageous in meeting the increased seismic and LOCA loadings and the associated safety requirements. The unique GAIA spacer grid behavior will be incorporated into AREVA NP's licensed methodologies to take full benefit of the increased mechanical robustness.

Sensitivity Analysis for Displacement-Controlled Finite-Element Analyses

Displacement-controlled finite-element analyses are typically employed to simulate the nonlinear static response of structural systems where a loss of load carrying capacity due to localized material failure and/or geometric nonlinearity is expected. To utilize applications such as reliability, optimization, and system identification for structural systems where the peak load capacity is a random variable or where the performance function is defined in terms of the applied load, accurate and efficient gradients of the displacement-controlled response are required. The direct differentiation method (DDM) is applied to the displacement control method in order to compute response sensitivity with respect to the applied load, which is treated as a variable within each pseudotime step. The resulting sensitivity gives the change in structural load carrying capacity with respect to changes in uncertain parameters. To verify the derived sensitivity equations, comparisons between the DDM and the finite-difference method (FDM) are performed through standalone sensitivity analyses of structural systems with material and geometric nonlinearity. Reliability analyses of a steel frame show the importance measures obtained when the performance function is defined in terms of the structural resistance to applied loads in a displacement-controlled analysis are similar to those obtained in a load-controlled analysis where the performance function is defined in terms of the structural displacements.

Void coalescence mechanism for combined tension and large amplitude cyclic shearing

Void coalescence at severe shear deformation has been studied intensively under monotonic loading conditions, and the sequence of micro-mechanisms that governs failure has been demonstrated to involve collapse, rotation, and elongation of existing voids. Under intense shearing, the voids are flattened, such that the void volume diminishes, whereafter the flattened crack-like voids rotate and elongate until interaction with neighboring micro-voids dominates the material response and coalescence sets in. Eventually, this leads to a complete loss of load carrying capacity. The severe shear loading, imposed at the far boundary, is in an early state of the deformation associated with significant stretching of parts of the void surface, while other parts remain practically un-deformed. A largely uneven distribution of the strain hardening, therefore, evolves along the void circumference and, thus, one cannot expect the void to return to its original shape in the case where the far-field loading is reversed. The present numerical work aims to investigate the evolution of micro-voids subject to constant tension and large amplitude cyclic shearing. The far-field loading, the void shape, and the void growth are monitored, and the calculations are pushed to coalescence and complete loss of load carrying capacity. The initially circular cylindrical voids are predicted to develop protrusions in the shearing plane with normal in the direction of the applied tensile load. These protrusions evolve during repeated cyclic shearing and spread towards neighboring voids - eventually being responsible for void coalescence.

ESTABLISHMENT OF CONCRETE DEPENDENCE OF DEPTH SOUNDING OF THE DISTANCE BETWEEN SEEKERS

One of today's most popular building material is concrete. This building material is not only well-known and commonly used, but also time-tested. And concrete building and high-rise buildings with their huge loads on the base and the shell of atomic reactors and storage of toxic waste. However, latent defects in concrete and reinforced concrete structures can be fatal and lead to serious economic, environmental and even humanitarian losses. Most often, the defects of constructions and structures are not caused by one factor, but as a result of their total effect, with a marked influence of any factor may cause increased effects of other factors. Defects found during the survey are divided into the following groups in order of importance: the defects that lead to the reduction and loss of load-carrying capacity; partially reducing the bearing capacity with a change in geometric dimensions; deviations in the geometrical dimensions while maintaining load-carrying capacity, causing unfitness for technical operation. Durability and stability of building structures depends quality of elements made of concrete or reinforced concrete. In practice, there is often a concrete examination methods cannot be used for in-depth assessment of quality of concrete structures for various reasons: because of the lack of bilateral access for measurement, because of the cramped conditions, inability to use destructive methods of control and need to be adapted to the conditions of the construction site with taking into account the structure of a particular product. This paper proposes a method for increasing the depth sounding at Concrete pipe coating by changing the distance between the points of acoustic contact. On the basis of experimental data derived from the dependence of the sensitivity of the instrument sounding base. Changing the design of the device holding the cone transducers, and the proposed scheme preliminary marking the concrete surface to minimize unexplored areas of concrete in a controlled area and increase the ka-operation control operations and thereby improve the reliability of the structure under construction.

Effect of the metastatic defect on the structural response and failure process of human vertebrae: An experimental study

BackgroundPathologic vertebral fractures are associated with intractable pain, loss of function and high morbidity in patients with metastatic spine disease. However, the failure mechanisms of vertebrae with lytic defects and the failed vertebrae's ability to retain load carrying capacity remain unclear. MethodsEighteen human thoracic and lumbar vertebrae with simulated uncontained bone defects were tested under compression-bending loads to failure. Failure was defined as 50% reduction in vertebral body height. The vertebrae were allowed to recover under load and re-tested to failure using the initial criteria. Repeated measure ANOVA was used to test for changes in strength and stiffness parameters. FindingsVertebral failure occurred via buckling and fracture of the cortex around the defect, followed by collapse of the defect region. Compared to the intact vertebrae, the failed vertebrae exhibited a significant loss in compressive strength (59%, p<0.001), stiffness (53%, p<0.05) and flexion (70%, p<0.01) strength. Significant reduction in anterior-posterior shear (strength (63%, p<0.01) and stiffness (67%, p<0.01)) and lateral bending strength (134%, p<0.05) were similarly recorded. In the intact vertebrae, apart from flexion strength (r2=0.63), both compressive and anterior-posterior shear strengths were weakly correlated with their stiffness parameters (r2=0.24 and r2=0.31). By contrast, in the failed vertebrae, these parameters were strongly correlated, (r2=0.91, r2=0.86, and r2=0.92, p<0.001 respectively). InterpretationFailure of the vertebral cortex at the defect site dominated the initiation and progression of vertebral failure with the vertebrae failing via a consolidation process of the vertebral bone. Once failed, the vertebrae showed remarkable loss of load carrying capacity.

Delamination-Debond Behaviour of Composite T- Joints in Wind Turbine Blades

Wind turbine industry utilizes composite materials in turbine blade structural designs because of their high strength/stiffness to weight ratio. T-joint is one of the design configurations of composite wind turbine blades. T-joints consist of a skin panel and a stiffener co-bonded or co-cured together with a filler material between them. T-joints are prone to delaminations between skin/stiffener plies and debonds between skin-stiffener-filler interfaces. In this study, delamination/debond behavior of a co-bonded composite T-joint is investigated under 0° pull load condition by 2D finite element method. Using Abaqus® commercial FE software, zero-thickness cohesive elements are used to simulate delamination/debond in ply interfaces and bonding lines. Pulling load at 0° is applied and load-displacement behavior and failure scenario are observed. The failure sequence consists of debonding of filler/stringer interface during one load drop followed by a second drop in which the 2nd filler/stringer debonds, filler/skin debonding and skin delamination leading to total loss of load carrying capacity. This type of failure initiation has been observed widely in the literature. When the debond strength is increased 30%, failure pattern is found to change in addition to increasing the load capacity by 200% before total loss of loading carrying capacity occurs. Failure initiation and propagation behavior, initial and max failure loads and stress fields are affected by the property change. In all cases mixed-mode crack tip loading is observed in the failure initiation and propagation stages. In this paper, the detailed delamination/debonding history in T-joints is predicted with cohesive elements for the first time.

Fracture mechanisms under monotonic and non-monotonic low Lode angle loading

Ductility of high-strength low-alloy steel S420MC was investigated by means of experiments and finite element analyses. Monotonic and non-monotonic low Lode angle experiments were carried out using double curvature specimens and punching tests. Punching tests allow investigating material behavior under zero Lode angle and from low to high stress triaxiality ratios. Investigated material exhibits significant increase of ductility with stress triaxiality decrease. Under low enough stress triaxiality, loss of load carrying capacity and fracture were not observed. Even if fracture is not observed under these conditions, pre-strains under very low stress triaxiality induce relative loss of ductility when the material is loaded again at higher stress triaxiality.

Immediate Deflection of Pretensioned Inverted T-Beam with Circular Web Openings Strengthened with GFRP Using Response Surface Methodology

The urgent need for a web opening in the pretensioned inverted T-beams after the construction for essential services causes local cracking around the opening which leads to decrease in stiffness and load carrying capacity. Therefore, strengthening the vicinity of the opening is essential to restore the loss in load carrying capacity of the beam using GFRP. To study the deflection of pretentioned inverted T-beam with web opening, three-dimensional finite element beam models are developed before and after GFRP strengthening using the finite element analysis (FEA). Modeling methodology and nonlinear analysis approach in ANSYS are presented. The results obtained from the FEA beam model are compared with the test data in terms of load-deflection curve. It has been concluded that FEA models are good representations for GFRP strengthened beams with web openings in terms of the number of elements, structural details, and, especially, reasonably accurate results in general.

One way RC wall panels with openings strengthened with CFRP

The urgent need for an opening in the reinforced concrete (RC) walls after the construction for doors, windows and essential services causes local cracking around the opening which leads to decrease in load carrying capacity (LCC). Therefore, strengthening the vicinity of the opening is essential to restore the loss in LCC of RC wall with cut-out opening. Sixteen of 1/3 scale RC walls with openings comprising four identical series of four specimens each were prepared and tested. Different sizes of openings were provided in the walls as percentage of total wall area: 5%, 10%, 20% and 30%. Series one and two designated as WO1–WO4 and WO1a–WO4a, respectively, are tested without Carbon Fiber Reinforced Polymer (CFRP), while series three and four designated as WO1b–WO4b and WO1c–WO4c, respectively, are tested with CFRP strengthened the vicinity of the openings with two different patterns. To resemble imperfections in constructions, the panels were subjected to a uniformly distributed axial load with an eccentricity of t/6. New constants have been incorporated in the empirical formula developed by Saheb and Desayi [1] to predict the ultimate load of one-way RC wall with opening strengthened by CFRP. In addition, this paper also reports the stress concentration factors around the openings and introduced a factor called strengthening factor to evaluate the increment in the LCC rate of RC wall with opening strengthened by CFRP. The results show that RC walls with openings strengthened by CFRP applied in 45° to the opening corners failed at load higher than failure load of their identical RC walls strengthened by CFRP applied along the opening.

POSTBUCKLING DEGRADATION FE ANALYSIS OF STIFFENED COMPOSITE PANELS

The capability of a commercial industrial tool, ABAQUS, to simulate the critical damage mechanisms in stiffened composite panels has been evaluated. The analysis and conclusions are supported by experimental results. The focus is on skin–stringer separation during compressive loading. Results show that the advanced degradation modeling capabilities present in commercial codes today may lead to an accurate characterization of the deep postbuckling range behavior and the collapse of stiffened composite panels. Compared to current design practice, where the first indication of ply failure or the onset of damage propagation is taken as the failure load, the methods used here provide a way to exploit the reserves in composite structures. It is concluded that implementing degradation mechanisms (composite ply and adhesive interface degradation) presents a significant improvement to simulate accurately the deep postbuckling states and collapse for stiffened composite panels with adhesively bonded stringers. The nature of the final loss of load-carrying capacity for this type of structures, by composite ply and adhesive interface failure, driven by postbuckling deformation, makes this simulation approach essential.

Structural Performance of Wood Plastic Composite Sheet Piling

This paper describes the structural performance of an innovative wood plastic composite (WPC) sheet piling. Tensile coupon tests were performed to determine tensile strength and modulus over a range of strain rates for both WPC and specimens cut from commercially available vinyl sheet piles. Full scale four-point bending tests were conducted up to failure on 20 sets of joined pairs of WPC Z-piles with four different span lengths. For comparison, bending and coupon-level tension tests were also conducted on commercially available vinyl Z-piles and coupons cut from them. The coupon-level tests indicated that WPC had on average a 14% greater modulus than the vinyl specimens in the initial linear range, defined as between 10 and 40% of the respective material’s ultimate tensile strength. However, if the modulus is computed over the same stress range of 10–40% of the WPC ultimate tensile strength, both materials have a similar modulus. The vinyl had a tensile strength 3.6 times that of the WPC. During the bending tests, the hollow cross section WPC Z-piles failed primarily in bending-induced tension, while the solid vinyl Z-piles exhibited buckling of the compression flange. Creep rupture testing was conducted for pair of WPC Z-piles in a four-point bending setup to determine long-term load-carrying capacity. No loss of load-carrying capacity was observed during the 90-day test and creep rates generally decreased during the test. However, creep deflections were larger than what would normally be exhibited by wood structural members. While additional studies are needed to address the effects of water absorption on WPC properties, the findings show promise for wood plastic composite light duty sheet piling retaining wall structures.

Strength and ductility of reinforced concrete slabs containing welded wire fabric and subjected to support settlement

This paper describes a numerical investigation of the impact of steel ductility and support settlement on the strength and ductility of continuous one-way reinforced concrete slabs containing low ductility welded wire fabric (WWF). A finite element model is developed for the investigation using the software ATENA and the results of a series of concurrent laboratory experiments are used to validate the numerical solution. A parametric investigation is conducted using the numerical model to investigate the various factors that influence structural behaviour at the strength limit state. The ductility of the main flexural reinforcement has a profound impact on the ultimate load behaviour of continuous one-way slabs subjected to support settlement, particularly when the reinforcement consists of cold drawn welded wire fabric. Both the strain at peak stress ( ε s u ) and the tensile strength to yield stress ratio ( f s u / f s y ) of the tensile reinforcement have a significant effect on the strength and ductility of reinforced concrete slabs, both with and without support settlement. When ε s u ≥ 5 % and f s u / f s y ≥ 1.08 (i.e. for normal ductility reinforcement), the reduction of strength caused by support settlements of up to span/100 is small and, for design purposes, can be ignored, even when significant redistribution of actions has been assumed. However, for low ductility reinforcement (i.e. when ε s u < 3.5 % and f s u / f s y < 1.05 ), support settlement may result in a significant loss of load carrying capacity. The load-deflection curves are brittle, even for the slabs with zero support settlement, and the slabs have little ability to undergo plastic deformation at or close to the peak load. In all cases with low ductility steel, fracture of the steel occurs at one of the critical sections at deformations not much larger than that at the formation of the first plastic hinge and failure is catastrophic, with little warning.

Development of Hybrid FRP-Concrete Composite Compression Members

The concrete-filled steel tubes have been widely used in buildings and civil structures. However the corrosion of the steel tubes results in the loss of load carrying capacities of the members and, therefore, there is a need for regular maintenance. To mitigate such maintenance issues and prevent the loss of load carrying capacity, FRP composite were suggested as the candidate material. A number of research works has shown that the use of FRP tubes produced by filament winding technique was very effective on the improvement of compressive strength of the concrete-filled FRP tubes (CFFT). However the filament wound FRP tubes did mot contribute to the increase of the flexural strength of a CFFT. In this paper, a new type of FRP tube which consists of several pultruded open sections assembled by filament winding technique is proposed to improve compressive strength as well as flexural strength of a CFFT. The load carrying capacity of proposed CFFT is discussed through the analytical investigation.

Critical time of a long multilayer viscoelastic shell

The buckling in stability of a long multilayer linearly viscoelastic shell, composed of different materials and loaded with a uniformly distributed external pressure of given intensity, is investigated. By neglecting the influence of fastening of its end faces, the initial problem is reduced to an analysis of the loss of load-carrying capacity of a ring of unit width separated from the shell. The new problem is solved by using a mixed-type variational method, allowing for the geometric nonlinearity, together with the Rayleigh-Ritz method. The creep kernels are taken exponential with equal indices of creep. As an example, a three-layer ring with a structure symmetric about its midsurface is considered, and the effect of its physicomechanical and geometrical parameters, as well as of wave formation, on the critical time of buckling in stability of the ring is determined. It is found that, by selecting appropriate materials, more efficient multilayer shell-type structural members can be created.

Influence of Surface Roughness on Non-Newtonian Thermohydrostatic Performance of a Hole-Entry Hybrid Journal Bearing

A general solution scheme to account the surface roughness and the cross-film viscosity variation of lubricant due to its non-Newtonian behavior and rise in fluid-film temperature for the analysis of fluid-film bearings is presented. The combined influence of surface roughness, non-Newtonian behavior of lubricant, and thermal effects on the performance of a hole-entry hybrid journal bearing system has been investigated. The surface roughness, especially stationary roughness (i.e., rough bearing and smooth journal) with a transverse pattern was found to partially compensate for the loss in load-carrying capacity due to the thermal and/or non-Newtonian behavior of lubricant effects. It limits 18.86% loss in load-carrying capacity due to the thermal effect to only 1.6% and 33.99% loss due to the combined influence of non-Newtonian lubricant and thermal effect to 16.76%.

Behaviour of thick composite tubes considering of delamination

The present paper deals with plane finite element analysis of thick composite tubes. Thick composite tubes are commonly used in marine industry and in deep-water offshore applications. Two kinds of interlaminar delamination type defect in a thick walled cylinder subjected to external pressure were confronted; an annular or ring like delamination and a strip delamination. Two finite element models were developed to predict the strain energy release rate at the delamination fronts. In these models the effects of the processing history of the composite material in the form of a uniform thermal load were also included to simulate the state of the residual stress in the composite. The considered defects are studied by means of the effect of buckling, investigating the annular and the strip delamination buckling, and the subsequent loss of load carrying capacity of the delaminated region.

Three-dimensional stress analysis and Weibull statistics based strength prediction in open hole composites

Abstract The critical failure volume (CFV) method is proposed. CFV is defined as a finite subvolume in a material with general nonuniform stress distribution, which has the highest probability of failure, i.e. loss of load carrying capacity. The evaluation of the probability of failure of the subvolumes is performed based on the lowest stress and thus provides an estimate of the lower bound of the probability of local failure. An algorithm for identifying this region, based on isostress surface parameterization is proposed. It is shown that in the case of material with strength following Weibull weak link statistics such a volume exists and its location and size are defined both by the stress distribution and the scatter of strength. Moreover the probability of failure predicted by using the CFV method was found to be close to that predicted by using traditional Weibull integral method and coincide with it in the case of uniform stress fields and in the limit of zero scatter of strength. Experiments performed on homogeneous epoxy resin plaques with and without holes showed that the predictions bound the experimentally measured open hole strength. The Weibull parameters used for prediction were obtained from testing only unnotched specimens of different dimensions. The effect of the hole size on tensile strength of heterogeneous materials such as quasi-isotropic carbon–epoxy composite laminates was considered next. Fiber failure was the only failure mechanism taken into account and a strain-based failure criterion was used in the form of a two parameter Weibull distribution. The stacking sequence was selected to minimize the effect of stress redistribution due to subcritical damage. Not unexpectedly an up to 30% underprediction of the strength of the laminates with small (2.54 mm diameter) holes was observed by using classical Weibull integral method as well as Weibull based CFV method. It was explained by examining the size of the CFV, which appeared to be below Rosen’s ineffective length estimate. The CFV method was modified to account for the presence of a limit scaling size of six ineffective lengths, consistent with recent Monte-Carlo simulations by Landis et al. [Landis CM, Beyerlin IJ, McMeeking RM. Micromechanical simulation of the failure of fiber reinforced composites. Mech Phys Solids 2000;48:621–48] and was able to describe the experimentally observed magnitude of the hole size effect on composite tensile strength in the examined range of 2.54–15.24 mm hole diameters.

Coupled Plastic Wave Propagation and Column Buckling

The plastic buckling of columns is explored in a regime where plastic wave propagation and lateral buckling are nonlinearly coupled. Underlying the work is the motivation to understand and quantify the dynamic crushing resistance of truss cores of all-metal sandwich plates where each truss member is a clamped column. Members are typically fairly stocky such that they buckle plastically and their load carrying capacity decreases gradually as they buckle, even at slow loading rates. In the range of elevated loading rates of interest here, the columns are significantly stabilized by lateral inertia, resisting lateral motion and delaying buckling and loss of load carrying capacity to relatively large overall plastic strains. The time scale associated with dynamic axial behavior, wherein deformation spreads along the column as a plastic wave, is comparable to the time scale associated with lateral buckling such that the two phenomena are coupled. Several relevant problems are analyzed using a combination of analytical and numerical procedures. Material strain-rate dependence is also taken into account. Detailed finite element analyses are performed for axially loaded columns with initial imperfections, as well as for inclined columns in a truss core of a sandwich plate, with the aim of determining the resistance of the column to deformation as dependent on the loading rate and the relevant material and geometric parameters. In the range of loading rates of interest, dynamic effects result in substantial increases in the reaction forces exerted by core members on the faces of the sandwich plate with significant elevation in energy absorption.