Subroutine USDFLD Research Articles

Novel FGM-USDFLD approach in Graded Cohesive Zone Modeling (GCZM): Predicting debonding and crack propagation in composite-patched notched plates

This study uses a graded adhesive approach to investigate the efficacy of composite patch reinforcement on a notched aluminum plate. The methodology employs the volumetric fraction concept of Functionally Graded Materials (FGM) to develop a Graded Cohesive Zone Model (GCZM). A variable field, introduced through a Fortran-based USDFLD subroutine, adapts the formulation of this GCZM. Patch debonding is simulated via adhesive damage using the Cohesive Zone Model (CZM). At the same time, crack initiation and propagation within the plate are modeled using the Extended Finite Element Method (XFEM) implemented in ABAQUS finite element software. The adhesive behavior is characterized by a triangular traction-separation law, with the GCZM incorporating gradation in both shear and normal separation modes relative to the notch radius. The GCZM concept is compared against two non-graded cases, Araldite 420 and AV138 adhesives, with one case replicating a previous study. Three gradation concepts are explored: C-1, where the more resistant Araldite 420 is located at the notch; C-2, at the extremity; and C-3, where it is at both the notch and extremity. These configurations aim to homogenize load transfer to the composite reinforcement and elucidate how different GCZM concepts influence debonding between the plate and composite reinforcement. By implementing USDFLD, this work effectively demonstrates the impact of gradation concepts and volumetric fraction indices on the competition between debonding and crack initiation in the plate. The results provide valuable insights into optimizing adhesive properties for enhanced structural integrity in composite-reinforced metallic structures.

Calibration of a constitutive model for polycrystalline diamond sintering process

Polycrystalline diamond is mostly pressed at high temperature in actual production. Thus, circumferential strain data of powder moulding are difficult to collect at high temperatures. As a result, the parameters of DPC constitutive model cannot be obtained using conventional testing methods. Moreover, the use of conventional equipment to test the mechanical properties becomes challenging because of the extremely high hardness and compressive strength of polycrystalline diamond. Sintering tests of polycrystalline diamond were carried out at 1360 °C and 223 Mpa using the spark plasma sintering (SPS) method, and displacement–load data were obtained. The spark plasma sintering experiment of polycrystalline diamond under high temperature and pressure was carried out using the Drucker Prager/Cap (DPC) model with relative density to obtain accurate displacement and load numbers. Combined with USDFLD subroutine, the experiment of polycrystalline diamond sintering was simulated on ABAQUS. Based on the complex method, ABAQUS-MATLAB platform is used for the reverse identification of constitutive parameters. The constitutive model parameters of polycrystalline diamond sintering process are obtained. This approach can describe the mechanical behaviour of polycrystalline diamond powder in the sintering process. In addition, the inverse identification method of the constitutive model in the sintering process of polycrystalline diamond based on ABAQUS and MATLAB solves the problem on the difficulty to observe the sintering of polycrystalline diamond under high temperature and high-pressure environment. Moreover, the constitutive model parameters of the sintering process are obtained, thereby reducing the cost and condition constraints in the actual experiment. A novel technique involves obtaining powder constitutive parameters at high temperature from the sintering point of view. This approach is important to simulate sintering of polycrystalline diamond and its composite products. Foundation itemNational Natural Science Foundation of China (Grant No. 52075438), the Key Research and Development Program of Shanxi Province of China (Grant No. 2020GY-106), the Open Project of State Key Laboratory for Manufacturing Systems Engineering (Grant No. sklms2020010), and the Open Research Fund of Key Laboratory of Oil & Gas Equipment of Ministry of Education (Grant No. OGE201702-110).

Exploring Advanced Functionalities of Carbon Fiber-Graded PEEK Composites as Bone Fixation Plates Using Finite Element Analysis.

This study aims to address the challenges associated with conventional metallic bone fixation plates in biomechanical applications, such as stainless steel and titanium alloys, including stress shielding, allergic reactions, corrosion resistance, and interference with medical imaging. The use of materials with a low elastic modulus is regarded as an effective approach to overcome these problems. In this study, the impact of different types of chopped carbon fiber-reinforced polyether ether ketone (CCF/PEEK) functionally graded material (FGM) bone plates on stress shielding under static and instantaneous dynamic loading was explored using finite element analysis (FEA). The FGM bone plate models were established using ABAQUS and the user's subroutine USDFLD and VUSDFLD, and each model was established with an equivalent overall elastic modulus and distinctive distributions. The results revealed that all FGM bone plates exhibited lower stress shielding effects compared to metal bone plates. Particularly, the FGM plate with an elastic modulus gradually increased from the centre to both sides and provided maximum stress stimulation and the most uniform stress distribution within the fractured area. These findings offer crucial insights for designing implantable medical devices that possess enhanced mechanical adaptability.

Numerical Study on the Responses of Suction Pile Foundations under Horizontal Cyclic Loading Considering the Soil Stiffness Degradation

This paper analyzes the deformation responses of single-cylinder and four-cylinder suction pile foundations in soft clay under horizontal cyclic loading. Based on the existing stiffness degradation model of soft clay, a more suitable model for marine soft clay is proposed by carrying out dynamic triaxial experiments under different stress levels. The stiffness degradation and cumulative displacement of soil under cyclic loading are implemented in ABAQUS by compiling a USDFLD subroutine. The rationality is verified by comparison with the displacement response of the pile measured by the centrifugal model test and the scaled model test reported in the literature. With the aid of the current model, the stress state and deformation of suction pile foundations under horizontal cyclic load are further analyzed. The numerical results reveal the path of soil stiffness degradation and the deformation response of foundations during horizontal cycling. The cumulative displacement generated by the cyclic load is quantitatively displayed. It is proved that this model has the capability to reflect the cumulative displacement under cyclic loading and shows promise in analyzing the long-term deformation response of offshore foundations.

Seismic responses analysis of monopile offshore wind turbines in clays considering the long-term cyclic degradation effect

In marine environment, the monopile offshore wind turbines (MOWTs) are subjected to long-term horizontal cyclic loads caused by wind, waves and currents, which will lead to the stiffness degradation and plastic cumulative deformation of clays. The decrease of clays bearing capacity caused by long-term cyclic degradation effect is a threat to the safe use of MOWTs in earthquake-prone countries (such as some countries in the circum-Pacific seismic belt). A three-dimensional finite element model is established to research the seismic response analysis of MOWT in clays considering the long-term cyclic degradation effect. The cumulative deformation of pile-soil system after long-term cycle are obtained by adopting the stiffness degradation of clays through the USDFLD subroutine. On this basis, the dynamic response analysis of MOWT system under the combined action of seismic and environmental loads is carried out. The influence of long-term horizontal cyclic load number, long-term horizontal cyclic load amplitude, seismic intensity, soil strength, environmental loads and cyclic degradation parameter on the dynamic response of MOWT is analyzed. In the seismic design of MOWTs, the effects of long-term degradation and random wind, waves and other environmental loads should be considered.

Failure analysis of composite pre-tightened teeth joints under bending and tension coupling load

With the application of composite pre-tightened tooth joint in engineering practice, relevant studies have found that in actual structures, the joints are subjected not only to axial tension but also to bending and tension coupling force. Therefore, to analyse the load mechanism and progressive failure process of the joint under bending-tension coupling, a experiment loading method for joint structure was first designed in this paper, and axial-tension and bending-tension coupling experiments of single and double teeth were carried out by this method. Then, a three-dimensional model of progressive failure based on the USDFLD subroutine and Tsai-Wu failure criterion is established based on the experiment condition, and finally, the progressive failure process of the joint in the case of bending-tension coupling is analysed by verifying the correctness of the finite element simulation. The study revealed that the top surface of the composite tooth is subjected to the combined effects of tension stress from the bending moment and tension stress from the axial force at the same time, so the joint damage starts at the top surface and the stress state at the top surface of the composite tooth needs to be considered.

Damage Analysis of CFRP Hybrid Bonded-Bolted Joint during Insertion of Interference-Fit Bolt.

In this study, experiments and finite element analysis (FEA) were used to evaluate the impact of interference-fit sizes on CFRP hybrid bonded-bolted (HBB) joint damage during bolt insertion. The specimens were designed in accordance with the ASTM D5961 standard and bolt insertion tests were performed at selected interference-fit sizes (0.4%, 0.6%, 0.8%, and 1%). Damage to composite laminates was predicted using the Shokrieh-Hashin criterion and Tan's degradation rule via the user subroutine USDFLD, while damage to the adhesive layer was simulated by the Cohesive Zone Model (CZM). The corresponding bolt insertion tests were performed. The variation of insertion force with interference-fit size was discussed. The results showed that matrix compressive failure was the main failure mode. With the growth of the interference-fit size, more failure modes appeared, and the failure region expanded. Regarding the adhesive layer, it did not completely fail at the four interference-fit sizes. This paper will be helpful in designing composite joint structures and especially for understanding CFRP HBB joint damage and failure mechanisms.

Thermo-hydro-mechanical behavior of a clayey rock: A constitutive approach and numerical validation

Temperature strongly affects the thermo-hydro-mechanical properties of clayey rocks. Using the Drucker–Prager Cap model and available experimental results, an advanced constitutive model is proposed to describe the influence of temperature on the hydro-mechanical properties of clayey rocks. To replicate the stress-strain behavior of clayey rock under the thermo-hydro-mechanical conditions, transverse isotropic properties are considered in the constitutive model. Attention is particularly focused on the stress-strain behavior of clayey rock at the plastic stage, the evolution laws of cohesion, friction angle, and pre-consolidation pressure are established by introducing factors such as elastic damage, plastic damage and hardening, and thermal damage. A hydraulic conductivity evolution law is presented, accounting for the thermal effect on water properties and porosity. Theoretical studies are implemented in the finite element method software ABAQUS FEA using the subroutine USDFLD. Some theory parameters are verified through back analysis. Finally, the experimental results and numerical simulations are compared, showing the superiority of the established theoretical model.

Influence of the angle between tibial and prosthesis mechanical axes on tibial bone remodeling in total knee arthroplasty.

Osteoarthritis of the knee is one of the most common diseases that affect the quality of life in the elderly population, and Total Knee Arthroplasty is considered the only real treatment for it, and as with any other surgery, a suboptimal technique may lead to an undesirable outcome. This paper aims to investigate the effects of the angle between mechanical axes of the tibia and the implant on the bone remodeling process. A 3D model was reconstructed using CT images, which was then used in an ABAQUS model with a USDFLD subroutine to simulate bone remodeling post TKA. The USDFLD subroutine compares the strain energy density from each increment to that of the previous increment to determine how the bone density will change. Simulation results suggest that when the prosthesis is inclined to one side, stress and density distribution increase, whereas stress and bone density decrease substantially on the opposite side. This decrease in bone density can be as much as 35% in the coronal plane. Sagittal malalignment results suggest that the effect would be relatively localized to the vicinity of the cutting plane. Results suggest uniform load distribution may be achieved when the two mechanical axes are kept parallel, which in turn can lead to decreased prosthesis loosening and bone fractures.

Failure Analysis of Hat-Stringer-Stiffened Aircraft Composite Panels under Four-Point Bending Loading.

Hat-stringer-stiffened composite panels have been widely used in aircrafts. Accurate failure analysis of them is important for the safety and integrity of the fuselage. During the service period, these panels will bear not only the lateral force caused by the bending of fuselage, but also the radial pressure caused by the internal and external differential pressure during the take-off and landing of the aircraft. However, the latter case lacks investigation. Therefore, experimental and numerical studies for the static and fatigue failure of hat-stringer-stiffened composite panels under four-point bending loading have been performed in this work. To accurately predict the fatigue failure, a novel theoretical model has been proposed based on the fatigue damage theory. In addition, a user-defined subroutine USDFLD is developed for the implementation of the proposed theoretical model in Abaqus. Experimental results show that the main failure modes are the delamination of the skin and debonding between the girder flange and the skin. The experimental average value of the initial debonding load and displacement in static tests are 897.3 N and 10.8 mm, respectively. Predictions exhibit good agreement with experimental results with relative errors within 10%. Experimental average fatigue failure life of the specimens is 33,085 cycles, which is also close to the prediction with relative errors within 10%. This indicates the reliability and applicability of the established theoretical model and numerical method for predicting the failure of hat-shaped girder structures.

3D progressive damage analysis of a unidirectional multi-layered composite for mechanical joints

ABSTRACT Due to the presence of holes in composite mechanical joints, stresses around the holes are increased, and they may cause failure in the composites. Analysis of the composite behaviour after damage initiation around the holes is important, complex, and mostly three-dimensional. In order to achieve accurate results about the composite failure modes, damage analysis using a modern criterion is needed. In this research, to investigate the damage behaviour of a unidirectional multi-layered composite plate of a mechanical joint under pure tension, three codes are prepared in the USDFLD, VUSDFLD and VUMAT subroutines based on the Hashin criterion and implemented in ABAQUS software. These codes, using the methods of suddenly and gradually degradation in composite properties, progressively simulate the three-dimensional damage behaviour of the composite plate after damage initiation. The results show that, when a mechanical joint is under pure tension, the adequate distance from the edge of a hole to the edge of a composite plate is about two times the hole diameter. Furthermore, it is found that to rapidly investigate and analyse a mechanical joint in the composite structures, the USDFLD subroutine, which uses suddenly decreased material properties after damage initiation, is reasonable and more efficient.

First and second order analysis of functionally graded composite material

This paper deals with the analysis of metal-ceramic (FGM) rectangular composite plate under transient loading conditions. Fully-Coupled Thermal-stress Transient analysis has been carried out and convergence study for peak stress and central deflection for various mesh size has been carried out and compared for both first and second order quad elements. Abaqus subroutine USDFLD has been used for spatially varying material properties of the FGM material. Volume fraction of the two constituents of the FGM is varied smoothly based on the power law for various values of porosity coefficient. Exponentially time varying temperature loading on the top and bottom surface of the FGM plate is considered with simply supported boundary conditions.

Numerical investigation to the cyclic loading effect on capacities of the offshore embedded circular foundation in clay

The effect of cyclic loading on the bearing capacity is significant problem in the geotechnical design of offshore foundations. This paper proposes a combined isotropic and kinematic hardening soil model, where the components of stain rate and strain softening are introduced, as to investigate the cyclic loading effect on the capacity of the offshore embedded circular foundation. The proposed model is well implemented by the aid of subroutine USDFLD in the commercial software of ABAQUS. The model reliability to predict the degradation of soil strength is validated at the elementary and model scale levels, with typical model parameters provided. Then, the examination of strain softening mechanism of clayey soil surrounding the embedded circular foundation is made, with the evolution of soften soil region (including the pattern and dimensions) under the cyclic horizontal and moment loading investigated. By a suit of cyclic loading analyses, the post-cyclic capacities against the numbers of cycles are reported and evaluated, with the effect of magnitude of vertical loading on the cyclic loading capacities represented by the shrinkage of combined loading failure envelops.

Development of Abaqus WCM plugin for progressive failure analysis of type IV composite pressure vessels based on Puck failure criterion

The type IV composite pressure vessels (CPVs) are used as a reliable solution for storing compressed gas but still require research and development to reach commercial advancements. The main two challenges in the design of CPVs are: a) debonding of liner and composite shell during the curing process, and b) accurate finite element modeling of the thickness and angle variation of helical layers at the dome regions. In this study, debonding of composite shell from polymeric liner and bosses due to the temperature variations during the curing process is simulated by using bilinear cohesive law. Regarding the second challenge, the Abaqus WCM plugin is used to model the actual geometry of two-liter type IV CPV’s domes by defining and controlling manufacturing parameters. The UVARM subroutine is developed to apply stress analysis and predict the damage initiation using the Maximum Stress, Tsai-Wu, Tsai-Hill, Hashin, and Puck failure criteria. Also, a USDFLD subroutine is written to implement progressive failure analysis using the Puck failure criterion with sudden material degradation model. The numerical axial and radial displacements as well as burst pressure results are compared with the experimental results available in the literature. A good correlation is observed between the finite element and experimental results. Also, numerical results showed that the initial debonding gap due to curing does not affect the progressive damage of the composite shell.

A numerical investigation and probabilistic analysis of excavation earth retaining wall instability caused by underground pipeline leakage

In recent years, underground pipeline leakage occurs frequently in urban regions, which seriously reduces the soil-structure stability in the vicinity of the leakage. In this paper, a numerical study about pipeline leakage-induced instability of adjacent excavation earth retaining wall (EERW) is carried out. To reflect the phenomenon of soil strength degradation when encountering leakage water, the relationship between soil strength parameters and saturation is established by using an empirical formula, which is then implemented in Abaqus via the USDFLD subroutine. After verifying the proposed simulation method, the instability time of EERW under different burial depths of the leakage pipeline is presented. In order to reflect the influence of underlying geotechnical uncertainties on the EERW performance and to improve the probabilistic computational efficiency, the neural network is used as a surrogate model to replace the tedious finite element modeling, and Monte Carlo Simulation (MCS) is used to calculate the time-dependent failure probability of the retaining structure. Extensive sensitivity analyses are carried out to explore the effect of random variables on the failure probabilities. Compared with the unsaturated soil permeability coefficient, the increase of the initial pipeline pressure has more pronounced influence on the stability of EERW, and the initial saturation shows completely different forms in the early and late stages of water leakage.

Nonlinear finite element analysis of PBL shear connectors in hybrid structures

The load-bearing capacity of perfobond Leisten (PBL) shear connectors in hybrid structures is represented by the shear-friction effect between the shear surfaces caused by the interlocking of aggregates when the fracture surface of the concrete dowel slips under an external load. To carry out an accurate numerical simulation of the bearing capacity and shear transmission mechanism of the PBL shear connectors, based on the secondary development function of the user subroutine, user-defined field variable subroutine (USDFLD), the effective simulation of the transverse shear expansion effect of the concrete dowel is achieved. A comparison with the results of the test data shows that the concrete damage plasticity (CDP) model demonstrates good robustness and convergence for the prediction and simulation of the damage characteristics of concrete structures. Based on the user subroutine USDFLD's automatic update function of material points and element integration points to field variables, this model effectively simulated the functional gradient model of the concrete dilatancy angle, the load on the shear connectors is always transmitted from the near load end to the far one, and the bearing capacity is clearly affected by the boundary conditions.

Investigation of the effect of the angle between femoral and prosthesis mechanical axes on bone remodeling of femur in total knee arthroplasty.

The bone remodeling is the process in which the bone adapts its structure to the variation of environmental loads. The joint might be broken or damaged as a result of aging or an accident. To remedy this situation, Total Knee Arthroplasty (TKA) and prosthesis implantation is recommended. The main goal of this research is to investigate the effects of femur implanting angle on the bone remodeling process after TKA in the Coronal, Sagittal and horizontal planes over seven years. First, the 3D CAD model from CT images is created then the bone behavior is simulated using a model with a USDFLD subroutine. The results show that as the implant rotates in one direction, the stress and density distribution increases in the same direction whereas the load and consequently the bone density decrease substantially in the opposite direction. Consequently, the bone density might even decrease 77 and 31 percent in the coronal and sagittal plane respectively, so in the total knee arthroplasty, the mechanical axes of prosthesis and femur should be parallel. The active bone which occurs as a result of mechanical axes of prosthesis and femur parallelism and consequently uniform load distribution, can protect the implant from prosthesis loosening and fracture.

A multi-state progressive cohesive law for the prediction of unstable propagation and arrest of Mode-I delamination cracks in composite laminates

In this paper, a finite element simulation study was performed on the dynamic crack propagation and arrest in double cantilever beam (DCB) specimens with interleaves. The expressions of crack initiation toughness, propagation toughness, arrest toughness, and kinetic energy during unstable crack propagation were theoretically derived based on the energy balance principle. The dynamic fracture toughness parameters were calibrated based on the DCB test results. For the simulations, a multi-state progressive cohesive law (MP-CL) suitable for quasi-static analysis was proposed, and the MP-CL parameters were introduced into the finite element model using the USDFLD subroutine in the ABAQUS software. The unstable crack stick–slip propagation behavior of the DCB specimens was successfully simulated, revealing the complex mechanical characteristics, such as the load–displacement response, kinetic and fracture energy, and crack propagation velocity, during unstable crack propagation. The simulation results were quite consistent with the experimental results, validating the correctness and effectiveness of the proposed model.

A finite element method based on modified Alonso unsaturated soil constitutive model

Based on the revised ALONSO model, combined with the ABAQUS software platform, this paper compiled the USDFLD subroutine and obtained the stress-strain curve and the axial strain-volume deformation by simulating the triaxial shear test of the unsaturated soil to control the suction and confining pressure. The curve verifies the accuracy and reliability of the algorithm. The research results show that: (1) When the suction is the same, the higher the confining pressure is, the higher the yield point of the soil sample is. According to the comparison between experiment and simulation, the modified Alonso model can reflect the nonlinearity of the stress-strain relationship of the reshaped unsaturated soil sample and its plastic flow characteristics; (2) Compared with saturated soil, unsaturated soil has a higher yield point as a result of the suction. And the larger the suction is, the higher the yield point is, which proves that the model can simulate the influence of unsaturated soil liquid relative to the solid phase.

A Numerical Approach to Analyze Detail Mechanical Characteristic at the Crack Tip of SCC in Dissimilar Metal Welded Joints

The mechanical characteristic at the crack tip is one of the main factors affecting the stress corrosion cracking (SCC) in dissimilar metal welded joints (DMWJs). In this research, to evaluate the effect of heterogeneous material properties on the mechanical characteristic at the crack tip of DMWJs accurately, a heterogeneous material model of the SA508 Cl.3‐Alloy 52M DMWJ was established based on USDFLD subroutine in ABAQUS. The comparison of the traditional “Sandwich” material model with the heterogeneous material properties, stress‐strain conditions, and the plastic zone around the crack tip at the interference zone has been analyzed by the finite element method (FEM). The results indicated that the heterogeneous material model could characterize the mechanical properties of the SA508 Cl.3‐Alloy 52M DMWJs accurately. In addition, the crack at the interface zone between materials will deflect along with the weld metal in two material models.