Reduction In Ultimate Strength Research Articles

CORROSION – BUCKLING INTERACTION OF 6061-T4 AL ALLOY FIXED – PINNED COLUMNS – EXPERIMENTAL STUDY

Compression buckling experimental tests was carried out for long and intermediatecolumns made of 6061-T4 AL- alloy. Two different soil corrosion time were adopted i.e.30days and 60 days using 27 samples. The experimental analysis revealed that increasing thecorrosion time negatively affects the mechanical properties of metals such as the specimensof 60 days corroded have 1.68% reduction in ultimate strength, also increasing the corrosiontime reduces the critical load such as the maximum reduction was 4.24% in critical bucklingload for 60 days corrosion time. Perry-Robertson theory was applied to the experimentaldata and it was found that the above theory can satisfactory predicted the critical bucklingload (Pcr) with a factor of safety equal to 1.2. The ratio of corroded Pcr to dry Pcr wasalways less than unity. This indication explains the effect of pitting corrosion on bucklingbehavior of 6061-T4 AL- alloy

Parametric study on structural behavior of tubular K-joints under axial loading at fire-induced elevated temperatures

Present research used the results of 405 finite element (FE) analyses to study the effect of the joint geometry on the ultimate strength and initial stiffness of tubular K-joints subjected to axial loading at fire-induced elevated temperatures. The FE models were validated against the data available from experimental tests. Structural behavior under different temperatures (200 °C, 400 °C, 500 °C, and 700 °C) was investigated and compared to the behavior at ambient temperature (20 °C). Results showed that by increasing the temperature, the ultimate strength and initial stiffness may decrease drastically. On average, the reduction of ultimate strength is 5%, 19%, 51%, and 83% at 200 °C, 400 °C, 550 °C, and 700 °C, respectively. A parametric study was conducted to investigate the effect of dimensionless geometrical parameters (β, γ, θ, and τ) on the ultimate strength and initial stiffness. Afterwards, ultimate strength data extracted from the FE analyses was compared with the values calculated from the equations proposed by available design codes in which the ultimate strength of the joint at elevated temperatures is obtained by replacing the yield stress of the steel at ambient temperature with the corresponding value at elevated temperature. It was indicated that this method may not have acceptable accuracy for carbon steel K-joints under axial loading. Hence, a new design formula was developed, through nonlinear regression analyses, to determine the ultimate strength of K-joints subjected to balanced axial loads at elevated temperatures.

열수노화 조건에서 레저선박용 탄소섬유강화플라스틱의 강도변화에 관한 실험적 연구

This paper deals with the experimental study on the hygrothermal ageing effect to the strength of Carbon Fiber Reinforced Plastics (CFRP) materials for marine leisure boat manufactured by vacuum assisted resin infusion method. The experiments performed consist of tensile, flexural and shear tests according to American Society for Testing and Materials (ASTM) and Korean Industrial Standards (KS) test methods. Test coupons are varied from uni-directional(UD, 0SUP0/SUP, 90SUP0/SUP), Bi-Directional (BD), and Double-Bias (DB) carbon fiber fabrics in conjunction with epoxy resin. The results of tensile test show that tensile strength reduces significantly while not the same degree of reduction is observed for elasticity modulus with respect to the existence of hygrothermal ageing effect. This implies that the tensile strain induced from external load holds steady values but ultimate strength values change widely under hygrothermal ageing effect. In case of the flexural test, 0SUP0/SUP UD shows more strength reduction than 90SUP0/SUP UD while BD has reduced values in both flexural strength and elasticity modulus under hygrothermal ageing effect. It is learned that the bending strain induced from external load and ultimate strength values are reduced with respect to hygrothermal ageing effect. Shear test performed only on DB materials, and the results show marginal reduction in ultimate strength and moderate reduction in elasticity modulus. This means that the shear strain varies more than ultimate shear strength with respect to hygrothermal ageing effect. The experiment conducted in this paper clearly demonstrates the differences in material properties of the CFRP for the consideration of hygrothermal ageing effect. Findings obtained from this experimental study can serve as a fundamental input data for the realistic structural responses of marine leisure boat built in CFRP materials.

The effects of voids on structural properties of fused deposition modelled parts: a probabilistic approach

In the search to understand the functional capabilities and limitations of fused deposition modelling (FDM) manufactured components, control over their structural behaviour is crucial. For example, voids introduced during the production phase are a large contributor to anisotropy, yet the magnitude of this contribution remains unquantified. As a baseline model for quantifying strength reduction due to process-induced voids, a statistical method for evaluation of the minimum residual (net) cross section is proposed and tested. Our new method serves to predict the reduction in ultimate tensile strength of transversely printed specimens relative to solid or longitudinally printed specimens, based on void sizes identified from microscopy images of the centre plane of a tensile specimen. ImageJ is used to identify void sizes from the microscopy images, and residual cross sections are determined using a bit counting MATLAB script. From the distribution of residual cross sections, the weakest link for a given sample size is estimated. The accuracy of the proposed method is determined through comparison with experimental test data for samples of polylactic acid (PLA). The results reveal a close yet slightly under-predicted strength estimate, which for the case considered predicted approximately 5 MPa (12%) lower strength than observed in the experiments. Based on our findings, we have established evidence that the anisotropic behaviour of FDM specimens in PLA can to a large extent be explained by the reduction in residual cross section. This implies that other effects such as fracture mechanics and atomic diffusion of polymer chains play a secondary role for the phenomena observed.

Structural behavior of tubular X-joints strengthened with collar plate under axially compressive load at elevated temperatures

This paper investigates elevated temperature resistance of circular hollow section X-joints reinforced with collar plates subjected to brace compression. A finite element (FE) model was developed and the results were validated against the data available from seven experimental tests. Also, the results of the present FE model were compared with the numerical results of other researchers. Afterwards, several 3-D FE-models of the collar plate reinforced X-joints were generated to investigate the effect of joint geometry and collar plate size on the initial stiffness, ultimate strength, and failure mechanisms at different elevated temperatures. Results showed that the use of the collar plates in X-joints at elevated temperatures (200 °C, 400 °C, and 600 °C, and 800 °C) leads to the significant increase of the initial stiffness and ultimate strength. Also, the increase of the plate length results in the less reduction in ultimate strength, at all elevated temperatures. But, the effect of the plate thickness on the reduction factor can be ignored. Moreover, the decrease of the β in the plate reinforced X-joints at elevated temperature can lead to the shifting of the maximum plastic strain from joint intersection to the toe of the weld joining the collar plate to chord member. The parametric investigation was followed by the non-linear regression analysis to propose a parametric equation for determining the ultimate strength of the collar plate reinforced X-joints under brace compression at elevated temperatures.

Decellularized materials derived from TSP2-KO mice promote enhanced neovascularization and integration in diabetic wounds

Decellularized biologic scaffolds are gaining popularity over synthetic biomaterials as naturally derived materials capable of promoting improved healing. Nevertheless, the most widely used biologic material – acellular dermal matrix (ADM) – exhibits slow repopulation and remodeling, which prevents integration. Additionally, engineering control of these materials is limited because they require a natural source for their production. In the current report, we demonstrate the feasibility of using genetically engineered animals to create decellularized biologic scaffolds with favorable extracellular matrix (ECM) properties. Specifically, we utilized skin from thrombospondin (TSP)-2 KO mice to derive various decellularized products. Scanning electron microscopy and mechanical testing showed that TSP-2 KO ADM exhibited an altered structure and a reduction in elastic modulus and ultimate tensile strength, respectively. When a powdered form of KO ADM was implanted subcutaneously, it was able to promote enhanced vascularization over WT. Additionally, when implanted subcutaneously, intact slabs of KO ADM were populated by higher number of host cells when compared to WT. In vitro studies confirmed the promigratory properties of KO ADM. Specifically, degradation products released by pepsin digestion of KO ADM induced greater cell migration than WT. Moreover, cell-derived ECM from TSP-2 null fibroblasts was more permissive to fibroblast migration. Finally, ADMs were implanted in a diabetic wound model to examine their ability to accelerate wound healing. KO ADM exhibited enhanced remodeling and vascular maturation, indicative of efficient integration. Overall, we demonstrate that genetic manipulation enables engineered ECM-based materials with increased regenerative potential.

ANFIS method for ultimate strength prediction of unstiffened plates with pitting corrosion

ABSTRACTIncreasing attention has recently been paid to the effects of localised pitting corrosion on the ultimate strength of marine structures. In this paper, an adaptive neuro-fuzzy inference system (ANFIS) method was developed to predict the ultimate strength reduction of steel plates with pitting corrosion subjected to uniaxial in-plane compressive loads. Published ultimate strength data-sets for unstiffened plates affected by pitting corrosion were used to train and test a series of ANFIS models composed of several input variables. To develop the best accurate model, rule-based fuzzy sets were used for mapping the inputs to the output using seven different types of membership functions. The two-sided Gaussian-type function was found to be more effective and less sensitive to the sample size than other functions tested. The developed method provided good estimates (maximum RMSE of 0.019) in comparison with published results obtained using the finite element and artificial neural network methods.

Post Deformation at Room and Cryogenic Temperature Cooling Media on Severely Deformed 1050-Aluminum

The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrained groove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at room and cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grain structure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattered diffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) of high-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the elongated grains with interior substructure were developed, which was responsible for the formation of 80% low-angle grain boundaries. The GOS map of the severely deformed specimen manifested the formation of 43% “distorted” and 51% “substructured” grains. The post deformation of severely deformed aluminum at room temperature led to the increase in the fraction of HAGBs from 20 to 60%. Also, it gave rise to the formation of “recrystallized” grains with the average size of 13 μm, which were coarser than the grains predicted by Zener–Hollomon parameter. This was attributed to the occurrence of appreciable grain growth during post deformation. In the case of post deformation at cryogenic temperature cooling medium, the grain size was decreased, which was in well agreement with the predicted grain size. The cumulative distribution of misorientation was the same for both processing routes. Mechanical properties characterizations in terms of nano-indentation and tensile tests revealed that the post deformation process led to the reduction in hardness, yield stress, and ultimate tensile strength of the severely deformed aluminum.

Evaluation of the air-borne ultrasound on fluidized bed drying of shelled corn: Effectiveness, grain quality, and energy consumption

ABSTRACTThe objective of the study was to investigate the influence of high power ultrasound on a laboratory-scale fluidized bed shelled corn dryer. The drying time, moisture content variation, specific energy consumption, and quality parameters including ultimate compressive strength, toughness, shrinkage and color of corn kernels were investigated. Furthermore, artificial neural network (ANN) simulation models were developed for predicting the drying variables. Machine vision techniques were used to determine color and shrinkage as qualitative indices. Results showed that the lower frequencies had better penetrations at lower temperatures and cause a significant reduction in drying time. In addition, the ultrasound application led to reduction of ultimate compressive strength and toughness of the dried samples although ultrasound has nonthermal character as the subsidiary factor, it plays an important role in shrinkage and color specification. Based on error analysis results, the prediction capability of ANN model is found to be reasonable for the developed models. Application of ultrasound significantly decreased the specific energy consumption of drying process at the optimal drying condition.

Ultimate strength assessment of plated steel structures with random pitting corrosion damage

Pitting corrosion poses a threat to plated steel structures serving in aggressive corrosion environments. This paper involves numerical studies on the structural behaviour and ultimate strength reduction of plated steel structures due to random pitting damage. Stochastic simulations were used to model the random nature of the pitting corrosion varying pitting shape, depth and distribution. A series of nonlinear analyses were performed on unstiffened plates and stiffened panels to understand the mechanisms of structural collapse due to random pitting damage. Empirical formulae were derived respectively for the prediction of ultimate strength reductions of unstiffened plates and stiffened panels in terms of regression analysis from the numerical results. Random pitting corrosion induces a variation and reduction in ultimate strength, and can lead to a transition in failure mode. The collapse of pitted structures under uniaxial compression has a feature that the onset of plasticity initiates in the areas close to the unloaded edge of the structure, and propagates into a continuous plasticity region linking the pits with highly concentrated stress. The pitted area with intensively stress-concentrated pits undergoes a locally amplified deformation that determines the failure mode, leading to structural failure.

Reduction in ultimate strength capacity of corroded ships involved in collision accidents

ABSTRACTThe objective of the study is to investigate the effects of sudden damage, and progressive deterioration due to corrosion, on the ultimate strength of a ship which has been collided by another vessel. Explicit finite element analyses (FEA) of collision scenarios are presented where factors are varied systematically in a parametric study, e.g. the vessels involved in the collision, and consideration of corroded ship structure elements and their material characteristics in the model. The crashworthiness of the struck ships is quantified in terms of the shape and size of the damage opening in the side-shell structure, and the division of energy absorption between the striking and struck ships for the different collision simulations. The ultimate strength of the struck ship is calculated using the Smith method and the shape and size of the damage openings from the FEA. In conclusion, the study contributes to understanding of how corroded, collision-damaged ship structures suffer significantly from a reduction in crashworthiness and ultimate strength, how this should be considered and modelled using the finite element method and analysed further using the Smith method.

Work hardening behaviour in banded dual phase steel structures with improved formability

In this work, we show how the presence of microstructural banding and segregation affects the work-hardening behaviour of a dual phase steel with improved formability. This steel contains chemical segregation inherited from the casting process. Our previously developed 3D cellular automaton model allowed us to design thermo-mechanical processes to either promote or suppress banding. The bands are properly described as in-plane sheets of martensite grains. Mechanical testing data revealed a significant reduction in tensile strength in banded structures for a similar level of ductility. The work-hardening behaviour in the pre-yield regime, including the yield strength itself, is not correlated to the incidence of segregation and/or microstructural banding. The reduction in ultimate tensile strength in banded structures stems from a reduced work-hardening capacity in the post-yield regime. This is due to increased austenite stability in the banded steels, coupled to the anisotropic strain localisation in the ferritic matrix between martensite bands.

Enhanced Stability of Retained Austenite by Quenching and Double Partitioning Process

In the present study, a novel quenching and double partitioning (Q&DP) process is proposed. The quenching and partitioning (Q&P) process was accompanied by a second partitioning process, which led to the enhanced stability of retained austenite. The chemical composition of the investigated steel was 0.24C-1.9Mn-1.85Si, without an excess addition of alloying elements. This process aims to enhance the stability of retained austenite by controlling martensitic transformation and carbon partitioning. By applying this process, the uniform and total elongation is increased, without obvious reduction in ultimate tensile strength. An optimum combination of strength and ductility (ultimate tensile strength: 1304MPa; total elongation: 23%) was achieved by quenching to 65°C and subsequent second partitioning treatment, after the first quenching to 300°C and partitioning process. The enhanced mechanical properties were attributed to the increased amount of stabilized film-like austenite.

Experimental analysis of residual ultimate strength of stiffened panels with pitting corrosion under compression

The collapse mechanics and ultimate strength of a stiffened plate with pitting damage are investigated experimentally with specimens with circular shaped holes representing the pits in the plate. A series of compressive tests has been conducted to investigate the effect of pitting corrosion, including the initial imperfections. The pit location, pit diameter and pit depth are examined to determine the influence of the pitting on the ultimate strength. The experimental results of load-displacement relationship, the strain response and the ultimate strength under compressive loads are analysed. The ultimate strength reduction is related with the degree of pitting or volume loss.

Experimental and numerical investigations of the composite behaviour in concrete-filled tubular columns with massive steel core at high temperatures

PurposeThis paper deals with experimental and numerical investigations of the composite behaviour within concrete-filled tubular columns with embedded massive steel core (CFTES columns). As the inner profile provides the main load-bearing capacity, the load introduction and transfer is of particular interest for the structural detailing of CFTES columns. Currently, no specific design regulations are available – neither for room temperature nor fire design. The presented investigations provide a basis for design recommendations and numerical approaches on reliable shear stresses.Design/methodology/approachThree series of push-out tests at room temperature and high temperatures are analysed in terms of ultimate shear strength, bond strength and shear strength-displacement-curve shape. The test parameters involve the steel core diameter and concrete cover, applying normal strength steel and concrete. Furthermore, a three-dimensional finite element model of the push-out tests is set up in Abaqus. The model implies temperature-dependent contact properties derived from the experimental tests using the cohesive behaviour method.FindingsThe test data reveal a distinctive reduction in both ultimate shear and bond strength for high temperatures. For high temperatures, the thermal expansion coefficients dominate the composite behaviour. Using the 3D numerical model and applying a temperature-dependent joint stiffness, maximum shear stress criterion and damage evolution, the observed composite behaviour can be described in a realistic manner.Originality/valueThe presented experimental investigations are unique, both concerning the investigated column type and performing push-out tests at high temperatures. For the first time, a temperature-dependent reduction of capable shear stresses is identified, which is crucial for the design of structural components.

Ultimate strength of hull structural stiffened plate with pitting corrosion damage under unaxial compression

Pitting corrosion can cause the ultimate strength degradation of hull structure. This research aims at the development of ultimate strength calculation formula of pitted stiffened plates under unaxial compression. Firstly, the relative parameters (such as sizes of stiffened plates, sizes and shape of pits, initial geometric imperfection and residual stresses of stiffened plates, boundary condition and type and size of finite element) of pitted stiffened plates in the finite element analysis were analyzed and assumed. Secondly, the effects of a few factors (such as distribution status, depth and position of pits, number of longitudinal stiffeners and sizes of stiffened plates) on the ultimate strength with respect to the corroded volume loss were discussed. Lastly, the ultimate strength reduction formulae of pitted stiffened plates based on corroded volume loss were obtained by the data analysis from lots of nonlinear finite element analyses.

Compressive and flexural behaviour of reinforced concrete permeable piles

Abstract Driven piles generate excess pore water pressures in the surrounding soil, where a full dissipation of these pressures may take a very long time. Measures are therefore sought to accelerate soil consolidation. The concept of permeable pile with drainage holes around the circumference of pipe pile could serve this purpose by providing drainage paths. However, the structural integrity of permeable pile may be deteriorated due to these openings. This paper presents the results of uniaxial compression and flexural tests on permeable and normal pile specimens. The influence of concrete strength and pattern of drainage holes in terms of diameter, total number and layers on the ultimate compressive strength is investigated. The crack pattern, deflection profile and concrete strains are measured for both normal and permeable piles. It has been found that drainage holes could cause the reduction in ultimate compressive strength, but the measured values are still far greater than design estimations. Moreover, the permeable piles have higher flexural capacity than the normal piles due to the stress redistribution.

Experimental study on durability of strengthened corroded RC columns with FRP sheets in tidal zone of marine environment

The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.

An Experimental Investigation and Numerical Analysis on The Behavior Of Reinforced Concrete Thick Slabs under Static Loading

This paper presents the testing results and numerical results of nine reinforced concrete thick slabs with and without openings. All slab specimens have the same planar dimensions (1000mm×1000mm) with three different thicknesses of (120mm,100mm,and 80mm).The slabs resting on 4 corner steel columns and tested under concentrated static loading up to failure. These slabs were also analyzed using nonlinear finite element method assuming nonlinear material properties. From the experiments, it was found that, The presence of openings in slabs supported on their four corners decreases the strength and rigidity of slabs to about (12-23) % depending on the slab thicknesses and the shape of these openings. The slabs with (circular opening) recorded a reduction in ultimate strength to about(20) % from those with square openings having an equivalent opening areas. The yielding of main steel reinforcement occurred at load about 85% of the slab ultimate load. The ultimate loads predicted by ANSYS model have showed a good agreement with the experimental results.

Experimental study on collapse of cracked stiffened plate with initial imperfections under compression

The collapse mechanics and ultimate strength of crack damaged stiffened plates are investigated by testing stiffened plates with an initial crack. A series of stiffened plates with initial distortions and with a crack are subjected to in-plane compression until achieving their ultimate strength. The crack position, length and the angle between the crack and longitudinal stiffener are changed for determining the influence of the crack on the plate ultimate strength. The ultimate strength and the strain response of the panels are reported. Finally, the ultimate strength reduction related with the presence of the crack and the failure mode are discussed for establishing a damage tolerant procedure for the design of ship structures.