Strain Contours Research Articles

Seismic performance of earthquake-resilient prefabricated corrugated web beam-column connection with buckling-restrained plates

This paper presents a developed prefabricated column-tree connection with buckling-restrained plates, which is suitable for conducting post-earthquake repairs. The core member of the buckling-restrained plates is made of low-yield point steel, which can yield repeatedly to concentrate damage and thus protect the main members of the beam and column under seismic loads. The structural behavior of the developed connection was numerically elucidated. The seismic design requirements, methods, and procedures of the developed connection were discussed in detail. A parametric study was conducted to investigate the effects of some parameters — e.g., the form of the bolt holes, the width, thickness, and length of the core member of buckling-restrained plates, and the gap between the restrained plate and beam flange — on the connection behavior. The hysteretic or skeleton curves, proportion of energy consumed in each component, and equivalent plastic strain contours were presented and compared. The results indicate that the developed connection has good ductility and excellent energy dissipation capacity. The damage can be concentrated on the core member of the buckling-restrained plates to protect the main members without a decrease in bearing capacity. The parameters of the core member of the buckling-restrained plates are recommended for design.

Wavy Trailing Edge Feasibility for Aircraft Engine Composite Fan Blade

Attempts to add the advanced technologies to aerospace composite structures like fan blade have been on in recent times to further improve its performance. As part of these efforts, it has been proposed that the wavy trailing edge could be used in the blade to reduce the noise level. It has been also proposed that it’s structural feasibility could be studied by fabricating coupons representing blade like boundary conditions and mimicking max strain contours of wavy trailing edge of blade and testing them. Suitable size coupons (baseline flat and ones with wavy edge) were designed, and appropriate boundary condition was suggested for tests. The four-point bend tests were performed on baseline flat and wavy edge coupons and after analyzing the results it was concluded that some wavy edge configurations coupons do show some knock down in the failure load/strain but the optimized wavy edge configuration coupons show almost no knockdown (within scatter) in the failure load/strains. This leads to the conclusion that the wavy edge configuration under consideration has sufficient structural integrity as per the representative coupon test

In-situ full-field measurements for 3D printed polymers during mode I interface failure

The fracture behavior of parts manufactured by fused filament fabrication (FFF) is highly driven by their mesoscale architecture characterized by the presence of weak interfaces between layers and filaments, likely to fail under loading. We propose an in-situ characterization approach to study the local phenomena driving the mode I interlayer and interfilament failure of FFF polymer specimens and support the development of a constitutive model for the interface damage. We provide full-field displacement and strain measurements by microstereoscopic digital image correlation (DIC) over a region of interest of around 4 × 3 mm2 in the proximity of the propagating crack for differently oriented interfaces. The high-resolution camera framework promotes the crack propagation monitoring and the crack length tracking until the specimen’s brittle failure. The local strain distribution reveals the distinctive mesoscale failure and damage mechanisms of 0°−0° and 0°−90° polylactic acid interlayer and interfilament interfaces. Overall, the 0°−90° stacking ensures higher fracture properties when compared to the 0°−0° counterpart, in agreement with the specimens’ force–displacement response recorded by the electromechanical testing device. Additionally, we propose a correlation between the strain contour plot heterogeneities observed for 0°−90° interlayer interfaces and 0°−0° interfilament interfaces and the specimens’ architecture inspected by scanning electron microscopy or X-ray computed tomography. Ultimately, the full-field measurements promote the development and validation of a constitutive model explicitly capturing the mechanical behavior of the interface.

On load-bearing and soil-reacting characteristics of hybrid pile-bucket foundations subjected to static horizontal loading

The hybrid pile-bucket foundation is an innovative alternative to monopile foundation when used to support offshore wind turbines (OWTs). To understand the load transfer mechanism of the hybrid foundation when loaded horizontally, reduced-scale model tests and numerical modelling were performed to investigated loading/deformation characteristics of the pile-bucket foundation structure and stress-reacting features of the soil surrounding the foundation. Both the pore water pressure (PWP) of the soil and strains of the pile and bucket are recorded from the model test. Furthermore, the pile/bucket load sharing ratio, contours of plastic strain, and excess PWP of the soil are obtained and analyzed via numerical modelling of the model test. The results show that the horizontal load is mostly carried by the bucket, and the overturning moment is mostly resisted by the pile. Compared to the monopile foundation, the soil of the hybrid foundation shows smaller PWP increase and less principle-stress rotation, implying a lower rate of stiffness and strength degradation of the hybrid foundation when subjected to cyclic loadings.

Experimental analysis of polymer matrix composite microstructures under transverse compression loading

Strengthening the fundamental understanding of micromechanical methods in continuity is a critical aspect in developing and designing future composite systems. Virtual testing has provided additional understanding of the behavior of materials on a microstructural scale. However, experiments must be executed to determine their validity. Modeling realistic microstructures under realistic loading conditions could help develop physically based micromechanical constitutive laws needed to predict their intrinsic failure. In this study, a micropillar with varying sizes was manufactured out of continuous fiber reinforced composites and transversely compressed to observe micromechanical phenomena. The fiber shape, size, and distribution were recorded as well as stress vs strain curves for each size of micropillar. The specimens were speckled to perform 2D digital image correlation (DIC) to analyze displacement and strain contours of the surface. The results from this study provides basic knowledge of microstructural instabilities, effects of nanovoids, interfacial debonded and matrix crack formation while under transverse compressive loading.

Numerical Analysis of the Seismic Performance of Rigid Beam-To-Column Moment Connections Equipped with Steel Slit Damper (SSD)

In the present research, the finite-element method (FEM) implemented in the ABAQUS software is used to evaluate several numerical models. This study presents a composite system of slit dampers coupled with column-attached seats, where excessive loading of the structural system leads to the yielding of the slit damper rather than damaging main structural elements, especially the beams. In this respect, four aspects of the behavior of such connections are herein investigated to come up with an in-depth insight; these include aspect ratio, distance ratio, compactness ratio, and thickness ratio. Variations of the mentioned ratios are explained and compared by assigning differences that can be applied based on the connection rotation hysteresis curve, displacement envelope curve, dissipated energy, plastic strain, and stress contour. According to the results of these studies, it was figured out that an increase in aspect ratio, a decrease in distance ratio, and/or a change in thickness ratio tend to lower the performance of a slit damper.

Constraint effect on fracture toughness resistance curves of an X60 pipe steel

The fracture toughness resistance curve (e.g. J-R curve and crack tip opening displacement (CTOD) or δ-R curve) is important in facilitating strain-based design and integrity assessment of oil and gas pipelines, where influence of ground movements and presence of planar weld flaws must be accounted for. In this paper, duplicate single edge bend (SE(B)) and clamped single edge tension (SE(T)) specimens with two different initial crack sizes were prepared from an X60 pipe steel. The longitudinally-oriented specimens were notched in the through-thickness direction and experimentally tested at room temperature. In general, the results showed the expected trends of higher resistance curves for both shallow-cracked versus deeply-cracked specimen types and tension versus bending loading modes. Eleven constraint parameters (i.e. QHRR, QSSY, QLM, QBM, A2, A2BM, h, Tz, Cp, Ap, Vp) were calculated based on three-dimensional (3-D) finite element analyses (FEA) for various tested SE(B) and SE(T) specimens.The results and analysis indicated that the shallow-cracked SE(B) specimens exhibited a constraint condition similar to the intrinsically low-constraint deeply-cracked SE(T) specimens. Among all of the constraint parameters, the Ap parameter based on the normalized equivalent plastic strain contour was found to have the most promising trend in terms of correlating the material’s toughness to constraint level for currently tested specimens. Further on-going investigations are underway to extend the evaluation to resistance curves for specimens made from X100, X80 and X70 pipe steels to allow for the characterization of strain hardening effect, as well as the evaluation of their associated weld metals and heat affected zones (HAZs).

Finite element simulation of liquid nitrogen temperature rolling of marine grade aluminium alloy 5754

Now days, numerical approaches are becoming an efficient practical tool for the analysis of elastoplastic behavior of various engineering materials. Present study elaborates about the numerical investigation of liquid nitrogen temperature (LNT) plate rolling operation of marine grade aluminium alloy 5754 (AA 5754) by finite element method. To serve this purpose, commercially available ANSYS software package has been utilized to perform LNT-rolling simulation. In literature, it is well documented that LNT-rolling immensely increases mechanical strength through grain refinement technique. During rolling at liquid nitrogen temperature, the dynamic recovery process is inhibited which leads in accumulation of high rate of dislocation defects. Consequently, with due rolling these accumulated dislocations attributed towards formation of ultrafine grain (UFG) structure. The aim of this work is to formulate an efficient method to numerically investigate the deformation characteristics of AA 5754 during LNT-rolling. Geometrical and experimental parameters like roller diameters, dimensions of flat plate, roller speed, friction coefficient etc. are incorporated in the preprocessor module of ANSYS software. An optimized meshed domain is selected for simulation of 40% thickness reduction of AA 5754. The temperature effect and corresponding stress distribution in the flat plate of AA 5754 is well captured and comparative analysis with the experimental practices has been successfully carried out. Numerical results obtained in the form of uniform thickness reduction, elastoplastic stress and strain contour plots, pressure force exerted by roller etc. are in good agreement with the experimental rolling operation.

A visual and full-field method for detecting quench and normal zone propagation in HTS tapes

A fast and effective quench detection method is especially challenging in the development of high-field high-temperature superconducting (HTS) magnets for their safe operations and reliably releasing the stored energy during a quench. The occurrence and propagation of a quench are often accompanied by strong thermal and magneto-mechanical responses within superconducting magnets. Aiming to detect a quench in the whole process and capture the thermoelastic behavior associated with it, a new detection technique with a visual and full-field perception based on the digital image correlation (DIC) method is proposed in the present study. The experiment of a quench triggered thermally by a local spot heater is conducted for a YBCO coated conductor tape in a cryogenic chamber. The evolution and characteristics of the full-field strain in the HTS tape during the processes of a non-quench, a quench occurrence and quench propagation are intuitively presented with experimental observations. For the comparison purpose, the conventional quench detection methods by monitoring temperature and voltage signals during a quench are also utilized experimentally. The results verify the visual and full-field quench detection method, which uses a criterion of thermoelastic strain-rate for the quench occurrence and the evolution of strain contours for the normal zone propagating aspect. Additionally, a numerical quench model of coupled thermoelasticity to simulate the experiment is established and solved with the aid of Comsol multiphysics software. The quantitative results are in good agreement with the experimental measurements to prove the reliability and availability of the developed detection method. Since the DIC method is non-contact and insensitive to intense electromagnetic interferences, it is expected to provide a new technique on quench issues and some basic measurements on strain/stress behaviors in extreme environments of high-field HTS magnets in the future.

Finite element modeling of sub-surface damage while machining aluminum based metal matrix composites

Sub-surface damage during machining of aluminum-based metal matrix composites (MMCs) has been modeled using finite element models. These models are based on reinforcement particles size and volume fractions and particles are distributed uniformly in the metal matrix. In order to simulate particle debonding cohesive zone elements (CZE) have been incorporated along the parting line. In addition, failure criteria based on brittle fracture have been added for ceramic particles to simulate particle fracture. To reduce computational time and simplify the model both CZE and particle fracture is limited to the reinforced particles along the parting lines facing the tip of the cutting tool. The damage depth beneath the machined surface is measured by using the non-zero plastic strain values in the equivalent plastic strain contours obtained from the FE models. The results were compared against published experimental data and found to be in good agreement.

Effect of surface preparation technique on fatigue performance of steel structures repaired with self-stressing SMA/CFRP patch

An experimental program was conducted to evaluate the effect of surface preparation on the effectiveness of a shape-memory alloy / carbon-fiber reinforced polymer (SMA/CFRP) self-stressing patch for repair and strengthening of fatigue-sensitive steel elements. Steel surfaces were prepared through grit blasting and power tool cleaning. The fatigue lives of control and repaired specimens were measured to quantify the improvement provided by the patch under Mode-I loading. Fatigue crack growth curves were developed using a beach marking technique to track the evolution of crack growth. Digital-image correlation techniques were implemented in selected cases to study the debonding of the patch from the steel for different configurations and load levels. The fatigue performance of repaired specimens is investigated in terms of failure modes, fatigue lives, crack growth curves, and strain contours. This discussion is informed by the results of surface characterization tests performed on grit-blasted and power-tool-cleaned surfaces. It was found that grit-blasted repaired specimens exhibit approximately three-times the fatigue life improvement experienced by their power-tool-cleaned counterparts.

Experimental investigation on the thermo-mechanical deformation of thermo-induced shape memory polyurethane

The influences of loading conditions on the shape memory effect (SME) of thermo-induced shape memory polyurethane (TSMPU) are investigated by series of thermo-mechanical deformation experiments. The variables related to mechanical responses and the strain contours are extracted to analyze the SME. It is shown that the recovery ratio gradually decreases and the residual strain gradually accumulates with the increase of number of cycles. Then, the internal stress is obtained from the experimental results under different deformation histories. It is unexpectedly found that there is a linear relationship between the internal stress and recovery ratio under the same peak strain with different strain rates and number of cycles. Meanwhile, the formation and release of internal stress as the deformation mechanism can reasonably reflect the influence of deformation history on the SME. The experimental results are useful to deepen the understanding of SME and establish a constitutive model considering the thermo-mechanical deformation history of TSMPU.

Nonlinear finite element study on element size effects in alkali-activated fly ash based reinforced geopolymer concrete beam

The practical application of geopolymer concrete structure is getting attention due to its environmentally friendly characteristics. This paper presents non-linear Finite Element Analysis (FEA) on the element size effect in reinforced geopolymer concrete beam. Element size significantly influences the failure mechanism of structure especially in ductile fracture of reinforced concrete. The critical failure strain, crack patterns and orientations are mesh sensitive in finite element analysis for reinforced concrete structure. The impact of the element size on behavioral aspects of reinforced geopolymer concrete beam such as the crack pattern, ultimate load capacity and load-displacement behavior studies discussed along with a formerly conducted experimental data. Further validation of FEA is carried out using the theoretical flexural strength of the beam according to Euro code 2. Results show that element size has a significant effect in capturing the cracking pattern of reinforced geopolymer concrete beam. FEA result from the positive principal strain contour confirms that the fine mesh size captured the tension, the diagonal shear and compression cracks, even the band of surrounding cracks around the bottom reinforcement, precisely as compared to coarse meshes. It has been observed that the utilization of fine mesh with 10 mm element size predicts the experimental and theoretical ultimate load by 99.46% and 96.11%, respectively. Coarse mesh having 25 mm element size shows slightly higher variation in predicting the experimental and theoretical ultimate load by 93.75% and 90.42%, respectively. In addition, fine mesh confirms the experimental mid-span vertical deflection by 99.44% however the coarse mesh predicts in significant deviation by estimating 48.04% of the experimental mid-span vertical deflection. Furthermore, the ductile failure of the beam was accurately traced by the fine mesh.

Structural Finite Element Simulation and Evaluation Method for Ship Collision Damage and Residual Strength of the Jacket

Introduction The vessel collision of jacket foundation in an offshore wind farm in the South China Sea happens frequently. Under this circumstance， the accurate assessment of the residual strength after structural damage has become an important technology of the safety of wind farm operation and maintenance. Method Based on the actual jacket structure of a wind farm in the South China Sea and considering the actual ship operation situation in the sea area， this paper used the finite element software ABAQUS to simulate the ship collision damage process of jacket foundation under different combinations of ship mass， initial velocity and collision angle. Result By using the quasi static method， the time interval of the collision forces and the plastic strain contours of the key nodes under different working conditions are concluded. Besides， the relationship between the maximum impact forces and impact factors and typical characteristics of the damage are concluded. Conclusion Based on the analysis， the typical change laws of the residual strength after the ship collision of the jacket are concluded to provide technological support for rapid assessment of the collision damage of related structures in the actual engineering process.

Investigating the mechanical performance of advanced marine coatings used for bonding composites to aluminum in-mold

ABSTRACT Advanced Marine Coatings (AMCs) are a combination of polyurethane technology with polyester technology. In this study, AMCs’ various formulations were tested for mechanical properties and lap shear strength between composite laminates and aluminum. Castings were fabricated for each formulation, and their mechanical properties were obtained through ASTM Testing. The lap shear strength between composite laminates and aluminum was determined by single lap shear testing. Numerical models were created to simulate the experimental lap joint testing and further analyze the adhesive at the joint using the mechanical properties obtained in this study. The numerical model was used to produce peel strain and shear strain contour plots of the adhesive and peel stress and shear stress distributions at the mid-layer of the adhesive at 85% failure load. The effects of changing the ratio of the polyurethane components on the AMC’s performance were also investigated. With the exception of failure shear strain, the mechanical properties were found to be inversely proportional to the amount of polyurethane added to the formulation. However, increasing the ratio of isocyanate to polyol increased the formulation’s mechanical properties at each formulation’s specified polyurethane percentage.

Tensile behavior of stainless steel 304L to Ni-20Cr functionally graded material: Experimental characterization and computational simulations

This study presents experimental and computational analyses of the phase composition and mechanical behavior of a functionally graded material (FGM) grading from 100 vol% 304L stainless steel (SS304L) to 100 vol% Ni-20Cr (NiCr) in 10 vol% increments. The mechanical behavior of the FGM was evaluated by extracting tensile specimens from SS304L-rich and NiCr-rich regions of the FGM, with the former behaving in a ductile manner and the latter being relatively brittle. The brittle response of the NiCr-rich sample was explained by the presence of the eutectic FCC+BCC phase in this sample, as identified by Scheil-Gulliver simulations along with experimental phase and composition analyses. The spatially varying yield and flow behavior of the FGM was determined through comparison of finite element analysis simulations with experimentally measured stress-strain curves and surface strain contours. The results highlight that the overall ductile behavior of SS304L and brittle behavior of NiCr are preserved in the SS304L/NiCr FGM but the formation of the brittle eutectic phase further reduced the ductility within the regions where it formed (90 vol% NiCr/10 vol% SS304L).

Characterization of heterogeneous creep deformation in vanadium-modified 2.25Cr1Mo steel weldments by digital image correlation

Low alloy ferritic steels are widely used to manufacture critical components that operating at elevated temperatures in the process industry, but a better understanding of the creep responses of their weldments are still needed to provide guidance for the design of high-temperature welded structures. In the present paper, the heterogeneous creep behavior of vanadium-modified 2.25Cr1Mo ferritic steel weldments was investigated by using the digital image correlation (DIC) technique. Three-dimensional plot of creep strain across the weld joint was constructed to intuitively represent the spatio-temporal evolution of creep strain for the base metal (BM), weld metal (WM) and the heat affected zone (HAZ). Combining the analysis of strain contour evolution during creep with the microstructural examination, it is found that creep strain was primarily concentrated in the HAZ, resulting in the creep cavitation at grain boundaries of the coarse-grain bainitic HAZ. In addition, BM exhibited a faster deformation rate than WM during creep. In order to quantitatively describe the heterogeneous creep deformation, a sub-region extensometer method based on the construction of virtual extensometers was proposed to obtain the representative creep strain data of individual regions of weldments. Furthermore, a parameter identification procedure combining a global optimization method (i.e. genetic algorithm) with an initial value determination scheme, was developed to determine the model parameters of BM, WM and HAZ for the hyperbolic-sine creep constitutive model. The results show that the heterogenous creep behavior of the V-mod 2.25Cr1Mo steel weldment can be well characterized by combining the sub-region extensometer method, the hyperbolic-sine creep constitutive model and its genetic algorithm-based parameter identification method.

Strain analysis of Moso bamboo (Phyllostachys pubescens) subjected to longitudinal tensile force

This study used digital image correlation (DIC) to perform a strain analysis of Moso bamboo (Phyllostachys pubescens) in the tangential section subjected to longitudinal tensile force to compare samples from outer/inner position of the culm wall. Simultaneously, an electrical resistance strain gauge (SG) was used to measure the strain profile for comparison with the strain analysis using DIC. During loading, the rate of the longitudinal strain between different positions was significantly different. As the load time increased, there was no difference in the rate of the transverse strain between the outer and inner samples, while the rate of the longitudinal strain for the inner sample was higher than that for the outer sample. Additionally, DIC showed that the longitudinal direction showed a relatively homogeneous strain contour compared to the transverse direction. Furthermore, the result indicated that the Poisson’s ratio was dependent on the positions of the bamboo in the radial direction of the culm wall. Using SG recording as a reference, the DIC revealed appropriate strain behavior of bamboo in terms of longitudinal and transverse strains within full-field area. Therefore, the DIC recording may help to characterize strain deformation on the bamboo during the application of a tensile force.

Nonlinear finite element models of reinforced concrete beams strengthened in bending with mechanically fastened aluminum alloy plates

This paper reports 3D nonlinear finite element (FE) models of reinforced concrete (RC) beams externally strengthened with mechanically fastened (MF) and externally bonded (EB) aluminum alloy (AA) plates. The measured and observed parameters of each specimen were obtained from an experiment conducted by the authors of this study. Each FE model adopted accurate material constitutive laws and appropriate element definitions to approximate the mechanical behavior observed during testing. A total of ten models were constructed based on the diameter, embedment depth, and arrangement of the expansion anchor bolt (EAB) as well as the presence or absence of epoxy. Results like the load-carrying capacity of the tested specimens as well as the failure modes like end-plate debonding (ED), local-plate debonding (LD), and plate rupture (PR) were accurately predicted. Additionally, Stress and strain contour plots were generated to investigate the FE models’ mechanical behaviors. Finally, a parametric study was conducted to illustrate the effects of the flexural steel reinforcement ratio and AA plate grades on the models’ structural response. It was concluded that the FE models could serve as a valid predictive platform for simulating the flexural behavior of RC beams strengthened with MF and EB AA plates.

Strain-rate dependency and impact dynamics of closed-cell aluminium foams

Strain rate sensitivity and deformation mechanisms of closed-cell aluminium foams under low-velocity impact loadings are investigated in this study. Instrumented drop-weight impact experiments and Finite Element (FE) modelling were conducted to explore the deformation rate dependency of aluminium foams (manufactured by CYMATTM corporation). An X-ray micro-Computed Tomography (XCT) reconstructed foam geometry was used in the FE modelling approach to explore actual deformation mechanisms and strain rate sensitivity of foams. The deformation and pore collapse mechanisms were explored through investigating the stress and plastic strain contours. Our results show that the FE modelling with rate-dependent material properties agreed with the dynamic experimental results. The foam showed significant rate sensitivity within the examined range of strain rates. Our modelling and experimental results collectively indicate that the rate sensitivity of the base material is the primarily responsible for enhancing strength during impacts. Furthermore, the FE modelling with rate-independent material properties and unique foam topology confirms the negligible inertia effect at low velocity impacts.