Predicted Failure Loads Research Articles

Prediction of failure load of RC and R-ECC dapped-end beams

The dapped-end reinforcements of a control beam have been designed conforming to requirement of the PCI code. The dapped-end reinforcements of other beams were derived from the control beam that involve the scheme variation of the hanger or diagonal reinforcements. Some selected beams utilize the engineered cementitious composites (ECC) in the dapped-end region. Twenty-seven large-scaled beams with dapped-end have been prepared, cast and tested. All beams were tested under the three-point loading up to failure. To localize effect of the shear failure, the shear span-depth ratio (av/d) of 1.43 has been carried out. Dapped-end beam (DEB) specified in PCI code has nominal shear span-depth ratio (an/d) less than 1, but in this study, several beams use an/d larger than 1. For analytical purpose, the design equations specified in PCI code have been used for the analysis requirement. By comparing against the test results, the analysis results that using the design equations of PCI code provide a significant difference, in which the mean value of analysis-test results ratio is 0.71. The design equations specified in PCI code were reliable to design the dapped-end reinforcements, but these equations have not yet able to accommodate adequately, in analyzing and predicting the failure load of DEBs that have the dapped-end reinforcements scheme varied.

Experimental and numerical study of S700 high strength steel double shear bolted connections in tension

This paper presents a thorough experimental and numerical study of the structural behaviour and resistance of S700 high strength steel double shear bolted connections subjected to tension. A total of 38 S700 high strength steel double shear bolted connections were adopted in the tests, and included seven 1-bolt connections (with each containing one bolt), ten 2-pe-bolt connections (with each containing two bolts arranged perpendicular to the load transfer direction), eight 2-pa-bolt connections (with each containing two bolts arranged parallel to the load transfer direction) and thirteen 4-bolt connections (with each containing four bolts arranged in two rows). The specimens were carefully designed with a series of geometric parameters, including the end distance, the edge distance, the longitudinal spacing and the transverse spacing, varied and examined. The test setup, procedures and key results, including the failure loads and modes as well as the load–elongation curves, were fully reported. Two types of failure modes, namely net section fracture and bearing failure, were observed from the tests, with their underlying mechanisms discussed. The effects of various geometric parameters on the failure loads and modes of the S700 high strength steel double shear bolted connection specimens were studied. It was generally found that the net section fracture behaviour and resistance are sensitive to the edge distance and transverse spacing, while the bearing behaviour and resistance are more dependent on the end distance and longitudinal spacing. The experimental programme was supplemented by a numerical modelling programme, where finite element models were initially developed and validated against the test results, and then used for conducting parametric studies to generate further numerical data over a wide range of geometric dimensions. The experimentally and numerically obtained failure loads and modes were then adopted to assess the accuracy of the relevant design rules for high strength steel double shear bolted connections in tension, as given in the European code, American specification and Australian standard. The results of the assessment revealed that (i) the American specification yields the most accurate failure load predictions on average, but with many over-predicted failure loads and inaccurate failure mode predictions, (ii) the Australian standard leads to less accurate but more consistent and safe predictions of failure load than the American specification, and (iii) the European code results in the most conservative and scattered failure load predictions among the three considered design codes, but with the best failure mode predictions. The development of improved design approaches for S700 high strength steel double shear bolted connections is underway.

Mechanical behavior of pressurized composite pipes made of various materials

Abstract In this study, multi-layered composite pipes with varied orientation angles and subjected to internal pressure were investigated by using the 3-D finite element method (FEM) and through experimental tests. The composite pipes were made of E-glass and T300/934 carbon fiber. The studies were carried out experimentally, analytically and numerically. The T300/934 carbon fiber reinforced composite pipes and E-glass reinforced composite pipes were given numerical model codes via ANSYS 14.5 software. These models were then compared with analytical results in the literature and with the experimental results. Finite element analyses (FEA) were carried out to predict failure loads. Each layer of the composite pipes was numerically examined from various orientation angles. Hoop and shear stress wereobtained numerically for each layer. Radial strain and radial stress were achieved in the radial direction of the composite pipes. Shear extension coupling was considered because the layup angles with + θ and - θ layers were in varied radii. Subsequently, the effects of the orientation angles were examined for all models. Moreover, it was found that an embedded adhesive joint is important for industrial applications.

Experiment and Numerical Simulation for the Compressive Buckling Behavior of Double-Sided Laser-Welded Al-Li Alloy Aircraft Fuselage Panel.

The aim of this work was to study the buckling behavior and failure mode of the double-sided laser-welded Al–Li alloy panel structure under the effect of axial compression via experimental and numerical simulation methods. In the test, multi-frequency fringe projection profilometry was used to monitor the out-of-plane displacement of the laser-welded panel structure during the axial compression load. In addition, the in-plane deformation was precisely monitored via strain gauge and strain rosette. The basic principles of fringe projection profilometry were introduced, and how to use fringe projection profilometry to obtain out-of-plane displacement was also presented. Numerical simulations were performed using the finite element method (FEM) to predict the failure load and buckling modes of the laser-welded panel structure under axial compression, and the obtained results were compared with those of the experiment. It was found that the fringe projection profilometry method for monitoring the buckling deformation of the laser-welded structure was verified to be effective in terms of a measurement accuracy of sub-millimeter level. The structural failure was caused by local buckling of the skin. The observed failure modes such as local buckling of the skin, bending deformation of the stringers, continuous fracture of several welds, and failure of local strength and stiffness were attributed to the deformed laser-welded panel structure under the axial compression. The predicted failure load in the numerical simulation was slightly smaller than that of the experimental test, and the error of the simulation result relative to the test result was −2.7%. The difference between them might be due to the fact that the boundary and loading conditions used in the FEM model could not be completely consistent with those used in the actual experiment.

Mechanical properties of 4 rocks at different temperatures and fracture assessment using the strain energy density criterion

This work aims to analyse the fracture behaviour of rocks with U-shaped notches subjected to mode I loading and to different temperature conditions. To this end, an energy-based approach is used called the Strain Energy Density (SED) criterion. This study attempts to extend a previous work of the authors where the SED criterion was successfully applied to U-notched components subjected to mode I loading conditions at room temperature. In this case, the effect of temperature is considered as a new variable.The research analyses four different types of isotropic rocks with different lithologies, namely a Floresta sandstone, a Moleano limestone, a Macael marble and a Carrara marble. An exhaustive laboratory campaign was performed to define the main mechanical properties of the selected rocks at different temperatures. In total, 144 tensile splitting (Brazilian) tests, 120 uniaxial compression tests, 410 thermal expansion measurements and more than 790 four-point bending tests have been executed under different thermal conditions. On the other hand, the range of temperatures analysed varies from room temperature up to 250 ºC, which is a common band in geothermal applications.Temperature has proven to be a significant parameter when analysing the fracture behaviour of the four selected rocks. Its influence on the main mechanical properties of the rocks (tensile strength, fracture toughness, compressive strength, Young’s modulus, Poisson’s ratio) has been studied and similar trends have been observed for the marbles, but different or even opposite ones for the sandstone and limestone. Overall, the application of the SED criterion has led to relatively accurate fracture predictions under different temperature conditions. This methodology assumes a linear-elastic behaviour of the rocks at the studied range of temperatures. For this reason, the failure load predictions become less accurate when non-linearities are not negligible, as in the case of the Carrara marble.

Fracture loads prediction of the modified 3D-printed ABS specimens under mixed-mode I/II loading

The fracture features of the 3D-printed samples are assessed employing Semi-Circular Bending (SCB) specimens. The critical failure loads are experimentally measured and have been predicted using both Maximum Tangential Stress (MTS) and Generalized Maximum Tangential Stress (GMTS) criteria. The 3D-printing process is improved with several approaches to decline the voids volume and escalate the weld lines strength of the 3D-printed specimens to boost their mechanical specifications. The Acrylonitrile Butadiene Styrene (ABS) SCB samples with numerous pre-crack angles ranged from pure mode I to pure mode II are produced utilizing a modified 3D-printing process. The results of the tensile tests confirmed that the properties of the specimens created by the modified 3D-printing process are independent of the raster of printing orientation. The predicted failure loads with the GMTS criterion had a better correlation with the experiment compared to the MTS criterion owing to the impact of the T-stress term in the 3D-printed SCB samples. Furthermore, the cross laminar fracture augmented fracture toughness and declined crack kinking behavior of the 3D- printed ABS specimens.

Rapid prediction method of failure load for hygrothermally aged CFRP – Aluminum alloy single lap joints

This paper presents an experimental study on the durability of adhesively bonded carbon fiber reinforced polymer (CFRP) – aluminum alloy single lap joints (SLJs) that are undergoing hygrothermal degradation. The failure loads of hygrothermally aged joints were measured and the corresponding fracture surfaces were investigated via visual observation and SEM. The variations of the Tg and the chemical components were determined by the DSC and FTIR analysis, respectively. The results demonstrate that the failure load of joints decreases nonlinearly as the aging duration increases, which approximates the exponential function. Cohesive failure is dominated before and after aging, meanwhile, the moisture absorption plasticizes the adhesive and leads to rougher fracture surfaces. The reduction in Tg and the FTIR results support the occurrence of a hydrolysis reaction in the adhesive due to hygrothermal aging. By quantitatively studying the relationship between the failure loads and the absorbance intensities of functional groups, a failure load prediction method was proposed. This method can establish the correspondence relationship between accelerated aging and actual service aging based on the chemical characteristics of adhesive, and realize the residual performance prediction of the bonding structure after hygrothermal aging rapidly and easily.

Optimum First Failure Loads of One- and Two-Core Doubly Curved Sandwich Shells

For fixed values of the areal mass density, product of the midsurface curvilinear lengths, and the choice from three unidirectional fiber (glass, graphite, or aramid) reinforced composites for facesheets, one- and two-core doubly curved sandwich shell’s geometries, fiber material, and fiber orientations for the facesheets are found that maximize the first failure load. Also determined are the locations of failure points and stress components significantly contributing to the failure, as well as the effects of uncertainties in values of material parameters on the failure load. The shell’s quasi-static and infinitesimal deformations are analyzed with a third-order shear and normal deformable plate/shell theory, in-plane stresses are found by using the plate theory deformations and transverse stresses using a one-step stress recovery scheme. The Tsai–Wu failure criteria, and honeybees inspired nest-site selection optimization algorithm are employed. Effects of uncertainties in material parameters are quantified by the Latin hypercube method and a statistical software, JMP. The predicted failure load and the failure point location agree well with their experimental values. It is observed that the first failure occurs in a core (facesheet) due to the transverse shear stress (in-plane transverse axial stress) exceeding its critical value. The methodology can be used to design the minimum weight optimal doubly curved multicore sandwich shells.

A pragmatic approach for a 3D material model considering elasto-plastic behaviour, damage initiation by Puck or Cuntze and progressive failure of fibre-reinforced plastics

Fibre reinforced plastics with tough epoxy and thermoplastic matrices are spreading increasingly in many lightweight applications. For an efficient and reliable design the mechanical behaviour, considering non-linear plasticity, various failure modes under complex loading and damage progression, has to be estimated with numerical simulations. Most state-of-the-art continuum damage mechanics models do not consider the non-linear behaviour of the matrix material or are not suited for 3D solid elements. This work proposes a combined 3D continuum damage/plasticity model. It uses a single parameter flow criterion in combination with Cuntze’s Failure Mode Concept (FMC) for intralaminar failure. The FMC requires no iterative fracture angle search as the Action Plane Strength Criterion by Puck (APSC). This work describes details of the developed model like the coupling of the FMC with a degradation model as well as the implementation into Abaqus/Standard. A validation against open-hole tension tests made out of AS4/PEEK from literature is performed. It can be shown that the prediction of experimental failure loads with the FMC as well as with the APSC provides comparable results. The maximum deviations are between -7.85% and +12.85%. However, the computation times for predictions with the FMC are significantly less than with the APSC.

Imperfection sensitivity analysis and DSM design of web-stiffened lipped channel columns experiencing local-distortional interaction

Cold-formed thin-walled steel members are commonly subjected to initial imperfection, which will greatly affect their load-carrying capacity. In this study, the load-carrying capacity and imperfection sensitivity of fixed-ended cold-formed steel web-stiffened lipped channel columns subjected to local-distortional (L-D) interactive failure (including secondary local bifurcation interaction (SLI), true L-D interaction (TI) and secondary distortional bifurcation interaction (SDI)) are investigated. A new imperfection simulation method combining finite element analysis (FEA) with the constrained finite strip method (cFSM) was firstly proposed, and then validated using experimental data from literatures. Next, 224 geometries of columns experiencing L-D interactive failure were chosen by the cFSM and their load-carrying capacity under normal state P num (with unavoidable minor initial imperfection) and those under imperfect state P imperfect (with various imperfections) were respectively obtained using FEA. The most unfavorable imperfection patterns for L-D interactive failure were summarized by comparing the P imperfect and P num of the members. Furthermore, the quality of the DSM-based design approaches for L-D interactive failure were evaluated by comparing P num with the failure load predictions of the selected columns provided by these design approaches. • An imperfection simulation method that combined FEM and constrained FSM was proposed. • The effects of imperfections on the thin-walled columns affected by L-D interaction were studied. • The accuracy and applicability of design approaches based on DSM were evaluated.

Effect of metastatic lesion size and location on the load-bearing capacity of vertebrae using an optimized ash density-modulus equation

About 1.8 million new cancer cases are estimated in the US in 2019 from which 50–85% might metastasize to the thoracic and lumbar spines. Subject-specific quantitative computed tomography-based finite element analysis (QCT/FEA) is a promising used tool to predict vertebral fracture properties. The aims of this study were twofold: First, to develop an optimized equation for the elastic modulus accounting for all input parameters in FE modeling of fracture properties. Second, to assess the effect of lesion size and location on the predicted fracture loads. An inverse QCT/FEA method was implemented to determine optimal coefficients for the modulus equation as a function of ash density. Lesions of 16 and 20 mm were then virtually located at the center, off-centered, anterior, and posterior regions of the vertebrae. A total of 6426 QCT/FEA models were run to optimize the coefficients and evaluate the effect of lesions on fracture properties. QCT/FEA predicted stiffness showed high correlations (50%) with the experimentally measured values. Compared to a 16 mm lesion size, a 20 mm lesion had a reduction in failure load of 55%, 57%, 52%, and 44% at the center, off-centered, anterior cortex, and pedicle, respectively (p < 0.001). Lesions affecting mostly trabecular bone showed the largest reduction in predicted failure loads (about 55%), and females presented weaker outcomes than males. An optimal elastic modulus equation resulted in accurate vertebral stiffness predictions. A deterioration of the trabecular bone due to the presence of a lesion highly affected the predicted fracture loads, and this reduction was significantly higher in females compared to males.

A method for predicting failure load of masonry wall panel based on structural stress state

This paper proposed a method for predicting failure loads of masonry wall panels subject to uniformly distributed lateral loading based on a concept of structural stress state. Firstly, the characteristics of the structural stress state of masonry wall panels subjected to uniform distributed lateral loading were investigated through experimental results. Then, a new parameter was proposed to characterize the structural stress state. Next, the relation of the failure loads between a specified base wall panels and other wall panel was established using the proposed parameter. In this way, a method (called a ST method) based on a structural stress state parameter to predict the failure load of masonry wall panel from the base wall panel was established. The following case studies validated the ST method by comparing the predicted failure load with the experimental results, as well as those predicted from the existing yield line theory (YLT), the FEA method and the GSED-based cellular automata (CA) method. The ST method provided an innovative way of structural analysis on the basis of structural stress state.

Mechanical behavior of pressurized composite pipes made of various materials

Abstract In this study, multi-layered composite pipes with varied orientation angles and subjected to internal pressure were investigated by using the 3-D finite element method (FEM) and through experimental tests. The composite pipes were made of E-glass and T300/934 carbon fiber. The studies were carried out experimentally, analytically and numerically. The T300/934 carbon fiber reinforced composite pipes and E-glass reinforced composite pipes were given numerical model codes via ANSYS 14.5 software. These models were then compared with analytical results in the literature and with the experimental results. Finite element analyses (FEA) were carried out to predict failure loads. Each layer of the composite pipes was numerically examined from various orientation angles. Hoop and shear stress wereobtained numerically for each layer. Radial strain and radial stress were achieved in the radial direction of the composite pipes. Shear extension coupling was considered because the layup angles with + θ and - θ layers were in varied radii. Subsequently, the effects of the orientation angles were examined for all models. Moreover, it was found that an embedded adhesive joint is important for industrial applications.

Cortical bone mapping improves finite element strain prediction accuracy at the proximal femur.

Despite evidence of the biomechanical role of cortical bone, current state of the art finite element models of the proximal femur built from clinical CT data lack a subject-specific representation of the bone cortex. Our main research hypothesis is that the subject-specific modelling of cortical bone layer from CT images, through a deconvolution procedure known as Cortical Bone Mapping (CBM, validated for cortical thickness and density estimates) can improve the accuracy of CT-based FE models of the proximal femur, currently limited by partial volume artefacts. Our secondary hypothesis is that a careful choice of cortical-specific density-elasticity relationship may improve model accuracy. We therefore: (i) implemented a procedure to include subject-specific CBM estimates of both cortical thickness and density in CT-based FE models. (ii) defined alternative models that included CBM estimates and featured a cortical-specific or an independently optimised density-elasticity relationship. (iii) tested our hypotheses in terms of elastic strain estimates and failure load and location prediction, by comparing with a published cohort of 14 femurs, where strain and strength in stance and fall loading configuration were experimentally measured, and estimated through reference FE models that did not explicitly model the cortical compartment. Our findings support the main hypothesis: an explicit modelling of the proximal femur cortical bone layer including CBM estimates of cortical bone thickness and density increased the FE strains prediction, mostly by reducing peak errors (average error reduced by 30%, maximum error and 95th percentile of error distribution halved) and especially when focusing on the femoral neck locations (all error metrics at least halved). We instead rejected the secondary hypothesis: changes in cortical density-elasticity relationship could not improve validation performances. From these improved baseline strain estimates, further work is needed to achieve accurate strength predictions, as models incorporating cortical thickness and density produced worse estimates of failure load and equivalent estimates of failure location when compared to reference models. In summary, we recommend including local estimates of cortical thickness and density in FE models to estimate bone strains in physiological conditions, and especially when designing exercise studies to promote bone strength.

Prediction of Load-Bearing Capacity of Composite Parts with Low-Velocity Impact Damage: Identification of Intra- and Inter-Ply Constitutive Models

Assessments of residual load-carrying capacity are often conducted for composite structural components that have received impact damage. The availability of a verified simulation methodology can provide significant cost savings when such assessments are required. To support the development of a reliable and accurate simulation methodology, this study investigated the predictive capabilities of a stacked solid-shell finite element model of a cylindrical composite component with a damage mechanics-based description of the intra-ply material response and a cohesive contact model used for simulation of the inter-ply behavior. Identification of material properties for the model was conducted through mechanical characterization. Special attention was paid to understanding the influence of non-physical parameters of the intra- and inter-ply material models on predicting compressive failure load of damaged composite cylinders. Calibration of the model conducted using the response surface methodology allowed for identifying rational values of the non-physical parameters. The results of simulations with the identified and calibrated finite element model showed reasonable correlation with experimental data in terms of the predicted failure loads and post-impact and post-failure damage modes. The investigated modeling technique can be recommended for evaluating the residual load-bearing capacity of flat and curved composite parts with impact damage working under the action of compressive loads.

Investigations on the strength of mechanical joints prepared from carbon fiber laminates with addition of carbon nanotubes

The present work is to examine the failure modes and failure loads in pin joints prepared from carbon/epoxy composite laminates with addition of multiwalled carbon nanotubes (MWCNT) as nanofillers. The effect of MWCNT in the carbon/epoxy composites was studied by adding 0.1 to 0.5 wt.% content in the epoxy resin. The maximum tensile strength was observed upto 0.3 wt.%, which is due to the enhanced interfacial bond strength and the efficient stress transfer between the stiff MWCNT and soft polymer matrix through refined polymer/MWCNT interface. The nanocomposite laminates for pin joints were prepared using optimised 0.3 wt.% of MWCNT. The different geometric combinations of width to diameter (W/D) and edge to diameter (E/D) ratios were varied from 2 to 5, respectively. The numerical analysis was performed using Hashin damage criteria along with progressive damage analysis to compare the predicted failure loads with the experimental results.

On the evaluation of a critical distance approach for failure load prediction of adhesively bonded dissimilar materials

The validity of the critical longitudinal strain method (CLS) was proved for a wide range of adhesives and substrates employed in bonding similar substrates (same substrate thickness and material). However, the recent need of weight reduction yields a challenge of joining dissimilar materials, especially where composite laminates are bonded to metal substrates. Based on this industrial demand, the need of using a simple approach for failure load estimation of dissimilar adhesive joints is increasing. The aim of this work is to extend the CLS approach to be able to predict the failure load of adhesively bonded dissimilar single lap joints (SLJs). To achieve this, dissimilar SLJs with a brittle adhesive were manufactured and tested. On the other hand, experimental results of other researchers were also considered where composite substrates were bonded to metal adherends. Based on the results, it was found that by doing a minor modification, the already developed CLS method can be successfully applied to dissimilar SLJs. It is shown that the modified CLS method is able to predict the failure load of dissimilar SLJs with both brittle and ductile adhesives.

Failure load prediction of a tubular bonded structures using a coupled criterion

In the context of increasing use of adhesive bonding for mechanical assembly, there is a need for reliable design tools. Both energetic and stress based conditions are necessary to predict the strength of bonded joints, which explains the use of a coupled criterion. The application of the criteria was performed by using Finite Element Analysis. Results obtained numerically were compared to experimental data from tubular bonded samples. A modification of the coupled criterion was proposed to take into account the loading rate in the prediction of the failure load. A good agreement was obtained between experimental and numerical predictions.

Tension failure analysis for bolted joints using a closed-form stress solution

Bolted joints are widely used to connect safety-critical parts in the aeronautical industry and require precise structural assessment tools. Focus of this paper is the development of an overall analytical calculation method to determine the stresses of a bolted joint with quasi-isotropic composite material, which is then used in a tension failure analysis. The stress solution is obtained by means of the Airy stress function. To predict crack initiation in the tension failure analysis use is made of the Theory of Critical Distances. Crack initiation occurs in the net section plane and its assessment requires precisely calculated net section stresses. For this purpose, the stress boundary conditions in load direction at the straight free edges must be fulfilled, which is reached by supplementing the field modelling the load introduction with auxiliary functions. This technique is a physically motivated means to deal with symmetric finite geometry problems involving straight free edges. However stress boundary conditions perpendicular to the load direction are not covered and some inaccuracies in the stress solution may arise. A failure analysis is conducted to investigate their impact on the predicted failure load using literature values based on Finite Fracture Mechanics as reference.

Conjugate Cellular Automata and Neural Network Approach: Failure Load Prediction of Masonry Panels

The intricate interplay between the microscopic constituents and their macroscopic properties for masonry structures complicates their failure analysis modelling. A composite strategy incorporating neural network (NN) and cellular automata (CA) is developed to predict the failure load for masonry panels with and without openings subjected to lateral loadings. The discretized panels are modelled by the CA methodology using nine neighbour cells, which derive their state values from geometric parameters and opening location placement for the panels. An identification coefficient dictated by these geometric parameters and experimental data is fed together as the input training data for the NN. The NN uses a backpropagation algorithm and two hidden layers with sigmoid activation functions to predict failure loads. This method achieves greater accuracy in prediction when compared with the yield line and finite elemental analysis (FEA) methods. The results attained elucidate the feasibility of the current methodology to complement conventional approaches such as FEA to provide additional insight into the failure mechanism of masonry panels under varied loading conditions.