Strain Contour Plots Research Articles

Biomechanical evaluation of additively manufactured patient-specific mandibular cage implants designed with a semi-automated workflow: A cadaveric and retrospective case study

ObjectiveMandibular reconstruction using patient-specific cage implants is a promising alternative to the vascularized free flap reconstruction for nonirradiated patients with adequate soft tissues, or for patients whose clinical condition is not conducive to microsurgical reconstruction. This study aimed to assess the biomechanical performance of 3D printed patient-specific cage implants designed with a semi-automated workflow in a combined cadaveric and retrospective case series study. MethodsWe designed cage implants for two human cadaveric mandibles using our previously developed design workflow. The biomechanical performance of the implants was assessed with the finite element analysis (FEA) and quasi-static biomechanical testing. Digital image correlation (DIC) was used to measure the full-field strains and validate the FE models by comparing the distribution of maximum principal strains within the bone. The retrospective study of a case series involved three patients, each of whom was treated with a cage implant of similar design. The biomechanical performance of these implants was evaluated using the experimentally validated FEA under the scenarios of both mandibular union and nonunion. ResultsNo implant or screw failure was observed prior to contralateral bone fracture during the quasi-static testing of both cadaveric mandibles. The FEA and DIC strain contour plots indicated a strong linear correlation (r = 0.92) and a low standard error (SE=29.32με), with computational models yielding higher strain values by a factor of 2.7. The overall stresses acting on the case series’ implants stayed well below the yield strength of additively manufactured (AM) commercially pure titanium, when simulated under highly strenuous chewing conditions. Simulating a full union between the graft and remnant mandible yielded a substantial reduction (72.7±1.5%) in local peak stresses within the implants as compared to a non-bonded graft. ConclusionsThis study shows the suitability of the developed semi-automated workflow in designing patient-specific cage implants with satisfactory mechanical functioning under demanding chewing conditions. The proposed workflow can aid clinical engineers in creating reconstruction systems and streamlining pre-surgical planning. Nevertheless, more research is still needed to evaluate the osteogenic potential of bone graft insertions.

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.

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.

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.

Bending mechanics of cylindrical skins for morphing aerospace applications

Shape-changing aerospace structures explore the trade-offs between aerodynamic performance and actuation efficiency. Herein, a morphing cylinder is optimized to minimize both its work to actuate in bending as well as radial deviations. Based on derived linear elastic mechanics of a cylindrical shell in bending, it was determined that favorable designs have high circumferential and low axial stiffnesses. We investigate circumferentially reinforced composites that limit radial displacement and allow for out-of-plane bending. Designs of flexible skins with embedded or underlying reinforcement were modeled, fabricated, and compared to unreinforced skins. Finite element analyses predicted the bending kinematics and structural responses. Digital image correlation used during the bending of physical prototypes generated strain contour plots of cylinder surfaces. Strong agreement between model predictions and experimental measurements was observed. The dimensions of each archetype were systematically varied via finite element modeling to obtain a set of nondominated designs capable of 25° of bending without buckling or large radial displacements. For the examined designs, it was determined that flexible skins reinforced with embedded rings were optimal at low (8–15 N·m) and high (>250 N·m) values for the work to articulate while flexible skins reinforced with underlying helical springs were optimal at moderate values (15–250 N·m).

Finite element modelling of Dyneema® composites: From quasi-static rates to ballistic impact

A finite element methodology to predict the behaviour of Dyneema® HB26 fibre composites at quasi-static rates of deformation, under low velocity drop weight impact, and high velocity ballistic impact has been developed. A homogenised sub-laminate approach separated by cohesive tied contacts was employed. The modelling approach uses readily available material models within LS-DYNA, and is validated against experimental observations in literature. Plane-strain beam models provide accurate mechanisms of deformation, largely controlled through Mode II cohesive interface properties and kink band formation. Low velocity drop weight impact models of HB26 give force-deflection within 10% of new experimental observations, with in-plane shear strain contour plots from models directly compared with experimental Digital Image Correlation (DIC). Ballistic impact models utilising rate effects and damage showed similar modes of deformation and failure to that observed in literature, and provide a good approximation for ballistic limit under 600 m/s impact speed.

Tensile Response of Epoxy and Glass/Epoxy Composites at Low and Medium Strain Rate Regimes

The present research work is to study the effect of low and medium strain rates on tensile behavior of epoxy and glass/epoxy composites. The digital image correlation (DIC) technique is employed for evaluating full-field strain contour plots using high-speed CMOS camera, which captures about 100,000 frames per second. Stress-strain measurements are reported for epoxy and glass/epoxy composites for strain rates ranging from 0.0001 – 450 s-1 and the variation of modulus, strength and strain to failure with strain rate is studied. A non-linear regression function is used to predict the tensile properties of epoxy and glass/epoxy composites at both low and medium strain rates regimes. The results reveal that the tensile strength and modulus increases with increase in strain rate for epoxy and glass/epoxy composites. The fracture surfaces of tensile specimens are investigated using scanning electron microscopy (SEM) to understand the influence of strain rate on fracture morphology.

Visualization of Fresh Cut Timber Deformation by Photogrammetry

Understanding the mechanical behavior of fresh cut timber, in which the natural moisture content has been retained, has application in predicting the behavior of living tree elements such as branch/stem joints, potentially inspiring structural designs through biomimicry. This project develops a process of strain imaging using particle image velocimetry to analyze behavior of timber samples freshly cut from oak tree joints and tested in tension. The timber surface was not coated so the fiber response could be visualized directly. Load was applied in steps and different methods for comparing images were trialled, including a sequential method in which strain is accumulated progressively from image to image and a first-to-last comparison. Sample flexibility caused significant deformation in the camera field of view, and so the analysis methodology was modified so that each image was compared sequentially with the first with the target area in the image for strain calculation expanded as the test proceeded. This resulted in strain contour plots able to show the impending failure of the component as the tension is applied.

Orientation dependence in superelastic Cu-Al-Mn-Ni micropillars

The superelastic behavior of single crystal Cu-Al-Mn-Ni shape memory alloy micro-pillars was studied under compression as a function of crystallographic orientation. Cylindrical pillars of about 2 μm diameter were micro-machined from targeted crystal orientations. While pillars oriented close to the [001] direction showed the largest total transformation strain (∼7%), plastic deformation dominated the compressive response in the pillars milled close to the [111] direction due to their high elastic anisotropy combined with the large stresses required to induce the transformation. Shape strain contour plots were constructed for γ′ and β′ martensites, and the martensite start stress was calculated using the Clausius-Clapeyron equation. The same general trends are observed in both the experimental and calculated results, with some exceptions: larger transformation stresses and lower transformation strains are observed in the microsized pillars.

Deformation in lead zirconate titanate ceramics under large signal electric field loading measured by digital image correlation.

Digital image correlation, a noncontact and nondestructive method, was employed to monitor the deformation of lead zirconate titanate piezoelectric ceramics. This method is based on imaging a speckle pattern on the specimen surface during the test and subsequently correlating each image of the deformed pattern to that in the reference state. In our work, both longitudinal and transverse strains were calculated from imaging a bulk sample under a ±2 kV/mm electric field. Compared with linear variable displacement transducer data, the results from this correlation method were validated. At the same time, based on this optical technique, different strain-electric field butterfly loops can be drawn from correspondingly selected regions of interest. Combined with contour plots of strain on the surface of the sample, the deformation of bulk ceramic sample under uniaxial electric field loading without any mechanical constraints is proven to be highly homogenous under macro-observing scale.

Theoretical investigation of tensile strained GeSn waveguide with Si₃N₄ liner stressor for mid-infrared detector and modulator applications.

We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect.

Photographic strain monitoring during full-scale failure testing of Örnsköldsvik bridge

Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test objects. This article reports the results of a ‘test-to-failure’ performed using a real bridge. The results obtained in such tests are valuable for assessing analytical models, updating finite element models and investigating the real behaviour of structures. The specific intention in these experiments was to study the shear failure of the bridge, which is a less well-understood mode of failure than is bending. To this end, it was necessary to strengthen the bridge using near-surface-mounted reinforcements made of carbon fibre–reinforced polymer bars in order to prevent bending failure. The bridge was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable differential transducers alongside new monitoring systems such as fibre-optic sensors, strain rosette linear variable differential transducers and a novel photographic monitoring system. This article presents the photographic strain measurements and describes the use of the photographic tools in monitoring and characterizing the behaviour of the failure zone during the full-scale test. The strains measured using the photographic method were found to agree well with those measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method provided crucial insights into the strains within the bridge’s failure zone. This study was conducted under the remit of the EU ‘Sustainable Bridges’ Project.

The effects of modeling simplifications on craniofacial finite element models: The alveoli (tooth sockets) and periodontal ligaments

Several finite element models of a primate cranium were used to investigate the biomechanical effects of the tooth sockets and the material behavior of the periodontal ligament (PDL) on stress and strain patterns associated with feeding. For examining the effect of tooth sockets, the unloaded sockets were modeled as devoid of teeth and PDL, filled with teeth and PDLs, or simply filled with cortical bone. The third premolar on the left side of the cranium was loaded and the PDL was treated as an isotropic, linear elastic material using published values for Young's modulus and Poisson's ratio. The remaining models, along with one of the socket models, were used to determine the effect of the PDL's material behavior on stress and strain distributions under static premolar biting and dynamic tooth loading conditions. Two models (one static and the other dynamic) treated the PDL as cortical bone. The other two models treated it as a ligament with isotropic, linear elastic material properties. Two models treated the PDL as a ligament with hyperelastic properties, and the other two as a ligament with viscoelastic properties. Both behaviors were defined using published stress–strain data obtained from in vitro experiments on porcine ligament specimens. Von Mises stress and strain contour plots indicate that the effects of the sockets and PDL material behavior are local. Results from this study suggest that modeling the sockets and the PDL in finite element analyses of skulls is project dependent and can be ignored if values of stress and strain within the alveolar region are not required.

Simple shear plastic deformation behavior of polycarbonate plate due to the equal channel angular extrusion process. I: Finite element methods modeling

AbstractSimple shear plastic deformation behavior of polycarbonate (PC) plates due to the novel equal channel angular extrusion (ECAE) process is modeled using a commercial finite element methods (FEM) package. The true stress and true strain contour plots as well as the strain rate variation across the PC plate during the ECAE process are analyzed. The FEM results correlate well with the experimental findings. The present study indicates that the novel ECAE process is effective in producing a high degree of simple shear plastic deformation across the extruded polycarbonate plate. The high degree of plastic deformation due to ECAE induces a high level of nearly uniform molecular orientation across the extruded PC plate. As a result, significantly improved physical and mechanical properties in PC are expected. The simple shear plastic deformation behavior of PC plate, as a function of extrusion rate and temperature, is investigated. The significance of the ECAE process for fabricating polymer parts is also discussed.

Computed tomography-based finite element analysis predicts failure loads and fracture patterns for vertebral sections.

Computed tomography-based finite element analysis represents a powerful research tool for investigating the mechanics of skeletal fractures. To provide evidence that this technique can be used to predict failure loads and fracture patterns for bone structures, we compared the observed and predicted failure behaviors of 18 midsagittal sections, 10 mm thick, cut from human vertebral bodies. The specimens were scanned by computed tomography, and finite element models were generated with use of empirically determined density-property relations to assign element-specific material properties. The specimens were loaded to failure in uniaxial compression, and the models were analyzed under matching conditions. The models provided predictions of yield load that were strongly correlated with experimentally measured values (r2 > 0.86) and were typically within 25% of measured values. Predicted stiffness values were moderately correlated with measured values, but large absolute differences existed between them. Comparisons between regions of observed fracture and of high predicted strain indicated that strain was an accurate indicator of the pattern of local fracture in more than two-thirds of the bone specimens. In addition, strain contour plots provided better indicators of local fracture than did stress plots in these heterogeneous bone structures. We conclude that computed tomography-based finite element analysis can be used successfully to predict both global and local failure behavior of simplified skeletal structures.

New techniques in the elastic analysis of arch bridges using image processing

AbstractThe importance of the masonry arch in Britain's infrastructure has never been more significant than at the present time with ever increasing axle loads under new EEC regulations The searches have been shown to be significantly affected by the overlying fill. The effect of this fill is being investigated by a number of methods employing a variety of experimental techniques. This paper presents one such new technique of examining the effects of the fill through monitoring zones of strain on an arch model subjected to load. The model arches were constructed in timber with a dry granular fill and approximately 90 tests were carried out to investigate the effect of load position, fill depth and pier stiffness. Image analysis of the tests permitted identification of the areas of strain within the fill and arch barrel and the location of the hinges at higher loads. Finite element (FE) analysis was used to model the arch in its elastic range and comparisons of the FE strain contour plots with the equivalent images illustrated the validity of using image processing for the determination of the strain characteristics. The practical applications of using such a technique are subsequently highlighted and commented on.