Cyclic Fatigue Loading Research Articles

Investigation of the structural performance and failure mechanisms of 3D printed continuous carbon fiber‐based composites

AbstractAdditive manufacturing of continuous fiber‐based polymeric composites has attracted global attention. This contemporary technology enables the flexibility of manufacturing customized, partially and fully functional, and advanced composite components for numerous semi‐structural and structural applications. The current study investigates the structural performance of 3D‐printed carbon fiber‐based composites in the context of tensile, flexural, and high‐cycle fatigue. The crucial S‐N curves for the unidirectional (UD) (0°) and cross‐ply (CP) (0, 90) composites have been plotted. The dominating failure mechanisms responsible for the failure of 3D printed composites under tensile, flexural, and high cycle fatigue loading at the micro‐scale have been thoroughly investigated. The influence of fiber orientation on the failure mechanisms under different structural loading has been rigorously studied. The current findings conclude that cross‐ply (0, 90) composites exhibited superior fatigue performance than the unidirectional composites when investigated at 70% of their ultimate tensile strength. The current investigation reveals that the formation of voids during 3D printing and majorly during loading is one of the leading causes of the failure of additively manufactured composites under mechanical and cyclic loads. The fiber pull‐out, fiber breakage, de‐bonding, and voids are the dominating failure mechanisms observed under tensile loading. In addition to the failure mechanisms listed under tensile loading, matrix fractures have also been observed under flexural loading. The dominating failure mechanisms differed for UD, CP (0, 90), and CP (45, −45) composites.Highlights Investigated tensile, flexural, and fatigue properties of continuous fiber 3D‐printed composites. Examined failure mechanisms under tensile, bending, and fatigue loading. Developed test coupons with built‐in tabs for tensile and fatigue testing. Cross‐ply composites showed better fatigue performance than unidirectional.

Micro-Defects-Related Low Cycle Fatigue Mechanical Model of the Nuclear-Grade S30408 Stainless Steel.

Continuous and interrupted low cycle fatigue tests were conducted on nuclear-grade S30408 stainless steel under different stress conditions at room temperature. Vickers hardness testing and microstructure characterization were performed on the fatigue samples with different fatigue states. The evolutionary mechanism of the microstructure defects in materials under fatigue cyclic loading was discussed. The traditional Basquin formula was used to predict the fatigue life of these fatigue samples. At the same time, a quantitative mechanical model related to the characteristic micro-defects parameter KAM and the Vickers hardness (Hv) was established for the S30408 stainless steel during the low cycle fatigue damage process, and the prediction accuracy of the Vickers hardness is greater than 90%, which is significant and useful for the fatigue life prediction of the 304 stainless steels used in nuclear systems and the safe operation of the reactors.

Prevention of the Fracture Problem Occurring in Automotive Alternator Heatsink Blocks Using Artificial Intelligence

In this study, prevention of fracture in vibration fatigue testing of automotive alternator heatsink blocks was investigated using an artificial neural network. Automotive components such as alternator heatsink blocks are subjected to high cyclic vibration fatigue loads throughout their lifespan, which can lead to the formation and propagation of fatigue cracks and ultimately component failure. The basic parameters affecting the resonant frequency of the heatsink blocks, including geometry and loading conditions, are determined. Data-driven decision making provides advanced predictive insights to analyze data for prediction and decisions using artificial intelligence approaches. An efficient artificial neural network model was defined to predict the resonance frequency in the vibration fatigue test. While the artificial neural network was trained to establish a functional relationship between the parameters and the resonance frequency, regression analysis was used to develop a predictive model to detect the resonance frequency of the heatsinks. The proposed approach aims to provide a comprehensive framework for preventing fracture problems in vibration fatigue tests of automotive alternator heatsinks and ultimately contribute to the reliable design and performance of these critical components. While the artificial neural network approach achieved high classification accuracy in predicting the new natural frequency, the regression model was also able to make accurate predictions. The results of this study showed that the time spent on design and simulation can be significantly reduced in preventing breakage problems that may occur before dynamic tests such as vibration tests of alternator components.

Analysis of Fatigue Crack Propagation in AISI 4140 Steel with Multi-Austempering Treatment

This study examines the fatigue crack propagation behaviour of AISI 4140 steel subjected to multi-austempering heat treatments. Tensile test and fatigue crack propagation (FCP) specimens were prepared in accordance with ASTM E8 and ASTM E647, respectively. Multi-austempering was carried out by heating the specimen to an austenite temperature for 10 min using an induction heating coil. The specimen was then immersed in a salt bath for each isothermal transformation time of 60 min at three austempering temperature levels from 312°C to 412°C with a temperature increase of 50°C. Tensile and fatigue crack growth tests were performed on both annealed and multi-austempered specimens. It is observed that the multi-austempering heat treatment significantly improves the tensile properties and the FCP properties of AISI 4140 steel. Microstructural observations indicate that the bainitic phase and the retained austenite increase the tensile strength and reduce the fatigue crack propagation rate (da/dN). It is found that the bainitic structures are an effective barrier in reducing fatigue crack propagation as the fatigue loading cycle increases

The effect of MWCNT concentration on the electrical resistance change characteristic of glass/fiber epoxy composites under low cycle fatigue loading

Abstract In this study, the effect of multi-walled carbon nanotube concentration on the electrical resistance change characteristics of multi-walled carbon nanotube filled glass/epoxy composites under low-cycle fatigue loading was experimentally investigated. For this purpose, multi-walled carbon nanotube concentrations of 0.2, 0.3, and 0.4 wt.% within composites were utilized to ensure electrical conductivity. The rectangular specimens for fatigue tests were manufactured by vacuum bagging method. The fatigue tests were conducted in a load-controlled manner with an ultimate strength ratio of 0.6 and at a stress ratio of 0.1. The results showed that the alteration in electrical resistance within the composites experiences a sharp and exponential rise when the concentrations of multi-walled carbon nanotube reach 0.2 and 0.3 wt.%, whereas the rate of this increase in electrical resistance is more gradual at 0.4 wt.%. multi-walled carbon nanotube concentration. The electrical resistance change curves of multi-walled carbon nanotube filled composites at various fatigue life levels were determined for statistical analysis using the Weibull distribution method. Finally, the average stiffness loss and the average residual fatigue life were determined at the electrical resistance changes corresponding to 95, 80, and 50 % Weibull reliabilities at various fatigue life levels and various multi-walled carbon nanotube concentrations.

Superelastic behavior of novel Ni–Ti–Co shape memory alloys for seismic applications

Abstract Ni–Ti–Co is a new shape memory alloy (SMA) composition that has a higher strength and a lower superelastic temperature range than the traditional binary Ni–Ti SMA composition. In this paper, the superelastic properties of Ni–Ti–Co bars that are important for seismic applications were studied and compared with those of Ni–Ti bars. The superelastic behavior, strength, strain recovery, low-cycle fatigue characteristics, and fracture strains of Ni–Ti–Co and Ni–Ti SMA with different heat treatment strategies and testing temperatures from −40 °C to 50 °C were investigated with seismic applications in mind. The effect of low-cycle fatigue loading and temperature variations on the superelasticity degradation of Ni–Ti–Co SMA were evaluated. The results showed that the yield stress of Ni–Ti–Co SMA at room temperature was 1.41–1.74 times that of the Ni–Ti SMA. Ni–Ti–Co SMA exhibited 100% strain recovery when unloaded from 5% strain in a temperature range from −40 °C to room temperature; while at 50 °C, a residual strain of 0.6% was observed when unloaded from 5% strain. For comparison, the Ni–Ti SMA lost superelasticity when the temperature was reduced to 0 °C. When subjected to low-cycle fatigue loading, the stability of the superelastic behavior (maintaining yield stress, energy dissipation and strain recovery) of Ni–Ti–Co SMA at −40 °C was better than that at room temperature and 50 °C. In particular, the superelasticity of Ni–Ti–Co SMA at −40 °C was superior to that of the Ni–Ti SMA at 0 °C. At −40 °C, the Ni–Ti–Co SMA showed almost no loss in yield stress, damping ratio and recovery strain during the first 100 cycles of fatigue loading. Moreover, from 100th to 471st cycle, at which the fracture occurred, the strain recovery of Ni–Ti–Co SMA showed almost no degradation.

Online fatigue crack detection and growth modelling through higher harmonic analysis: A baseline-free approach

This paper presents a novel baseline-free online method for fatigue crack detection and growth modelling of aluminium plates based on the relative second harmonic parameter β′ˆ, which is defined as the ratio of the amplitude of the fundamental frequency A1 over the square of the second harmonic frequency A2, obtained from the response under cyclic fatigue loading. Results reveal that β′ˆ is an effective parameter for online detecting the crack length less than 2 mm and estimating the remaining life, without requiring a baseline signal obtained from the pristine condition. Subsequently, the quantitative relationship between Fatigue crack growth (FCG) and the parameter β′ˆ is developed based on the quadratic polynomial fitting. The reliability of the method is assessed with the Root Mean Square Error (RMSE) and 95% confidence interval. Finally, the robustness of the proposed approach is evaluated by testing specimens with different sensor locations, thereby mitigating the potential sources of uncertainty arising from sensor locations. Results from this research provide a new strategy for online crack detection and growth modelling under fluctuations in loading and boundary conditions.

Fatigue performance of stainless steel bolts in tension under variable amplitude loading

This study experimentally investigates the variable amplitude fatigue performance of A4–70 stainless steel bolts under axial tensile loading. Static tests were first performed to establish the load-axial elongation relationship. Constant amplitude and variable amplitude fatigue tests were subsequently conducted to obtain the fatigue loading cycles and failure modes. The fracture surfaces were inspected via macroscopic and microscopic morphology analyses. The fatigue performance was eventually evaluated in terms of SN data, and the equivalent fatigue strength of the bolts under variable amplitude loading was calculated based on their cumulative damages. The predictions of several international design codes for bolt fatigue were compared with the test results to verify the feasibility of these provisions. The results of the study showed that the bolt fracture surfaces possess significant morphology features representing the respective fatigue damage progresses. The fatigue performance of the stainless steel bolts under variable amplitude loading is influenced by the loading sequence and load amplitude. Current design codes can provide conservative predictions of the fatigue life of A4–70 stainless steel bolts in tension.

Study on the effect of stress redistribution in different notched specimens of DD6 on the life of combined high and low cycle fatigue under high temperature

Under combined high and low cycle fatigue (CCF) loading, the multi-axial stress state induced by geometric discontinuities of different notch forms under the same stress amplitude can result in significant differences in fatigue performance of DD6 alloy. Therefore, it is of great importance to study the CCF behavior of Ni-base single-crystal alloy samples with differing notch geometries at the high temperatures. In order to obtain an approximate CCF lifespan, different stress amplitudes need to be applied to DD6 specimens with different notch forms. In this study, two kinds of notched DD6 plate specimens with [001] orientation were studied by CCF test at 760 °C, and the amplitudes of stresses were acquired under the same service life level. The effect of stress redistribution, in particular stress triaxiality, was evaluated on CCF lifetime of the DD6 specimens. A damage model with anisotropy considering stress triaxiality effect was suggested. The results indicated that the conventional stress–strain variables could not reflect the trend of CCF lifetime for different geometrical notched DD6 specimens, whereas the stress triaxiality at the CCF load peak could. A modified Basquin model was introduced for predicting CCF life according to the stress triaxiality at the peak loading. It can accurately and efficiently estimate the CCF life of two kinds of notched DD6 plate specimens, and the life prediction results fall within a scatter band of ±3 times of fatigue life.

Peculiarities of formation and processing of surface interferograms according to Twyman-Green scheme in non-destructive testing

The goal of the work is to ensure the maximum accuracy of reconstruction of relief and de-formation displacement fields of structural element surface by the interferometric method. The authors successfully use novel algorithms for the processing of surface interferograms as well as the interferometers that follow the Twyman-Green scheme in order to implement such opti-cal testing of the surface. The maximum precision of obtained experimental data was achieved by the use of structural additions to the optical circuit and the selection of optical elements and their settings during adjustment of the interferometer, as well as new algorithms for the selec-tion and registration of a series of interferograms, speckle interferograms and speckle surface images. The authors proposed structural additions to the interferometer scheme used in the testing of both smooth and rough surfaces, appropriate methods for calculating the parameters of optical elements and their adjustments. Examples of obtained interferograms of the surface of metals under the static and fatigue cyclic loading, speckle interferograms of the surface of metals and polymer composites under the static and dynamic loading are given. The results of processing and interpreting these interferograms confirm that the Twyman-Green interfero-meter is an effective instrument for solving the problems of fracture mechanics and deformable solids. In particular, an assessment was made of: roughness and waviness of the surface of metals; sizes of the plastic zone around the stress concentrator; deformation displacement fields of metals and composites, as well as the detection of hidden defects in them.

Stiffness Optimization of Squirrel Cage in Aircraft Engines

squirrel cage is a component used in engine shafts to make the shaft stiffer and able to withstand high cycle fatigue loads continuously for a long time. A squirrel cage can be of many shapes and sizes. The critical speed and the stresses acting on the shaft play a key role in determining the performance of shafts in engines. The squirrel cage in the shaft absorbs stress and extends shaft life. This paper deals with the structural design and analysis of the squirrel cage of an aircraft engine. The design of the squirrel cage was done on SolidWorks, and analysis was carried out on the Ansys workbench. To meet the strength and stiffness, the squirrel cage was optimized by introducing slots in it. Stress analysis of the bearings has been carried out for axial and radial loads from 1 to 20 kg. The radial load is applied to individual bearings, and then the axial load is applied to only one bearing. Then results are plotted into curves, and a slope is obtained based on deformations obtained. The stiffness value is noted, and the same procedure is performed for an optimized slotted squirrel cage. These values are compared, and then the squirrel is proved to be weight optimized and has improved stiffness.

Effect of Constant Cyclic Stress Coupling on the Fatigue Behavior of 304LN Stainless Steel.

The stress state of the primary circuit main pipeline is very complex mixed constant stress and periodic cyclic stress during the operation of nuclear power plants, which often affects the failure behavior of the stainless steel (SS) pipe. The fatigue behavior of 304LN SS under mixed constant stress and cyclic stress was investigated, and it was found that the coupling effect of constant stress and cyclic stress has a significant collaborative acceleration on the fatigue behavior. The research results showed that the cracks in the 304LN SS did not propagate even after 78 days under both constant load conditions of 5 KN and 7.5 KN, while the crack growth rate (CGR) of the specimen increased by about an order of magnitude when coupled with a cyclic fatigue load. The fatigue life of 304LN SS was the longest under 200 °C high-temperature water, and its life was roughly the same under 250 °C and 300 °C water. In a 300 °C high-temperature water environment, the fatigue life under the coupling of constant stress and cyclic fatigue stress is significantly lower than that under symmetric cyclic stress alone. There is a synergistic acceleration effect on the fatigue life of 304LN SS when constant stress is coupled with periodic cyclic stress, which is attributed to the combined effect of a corrosion environment and mechanical factors.

Elevated-temperature performances of Al-Si-Cu casting alloys for cylinder head applications

In this study, high-temperature properties of two newly developed Al-Si-Cu alloys (2Cu and 3.5Cu alloys) were investigated and compared to the commercial-grade A356 + 0.5Cu alloy (R alloy). 3.5Cu alloy exhibited the highest strength, outperforming R alloy by over 50 MPa at room temperature and by more than 20 MPa at elevated temperatures in ultimate tensile strength. However, R alloy demonstrated three to four times higher elongation than 3.5Cu alloy at room temperature, though this difference diminished at high temperatures. The minimum creep rate of 3.5Cu alloy was 2.4 times lower than that of 2Cu alloy and 14.5 times lower than that of R alloy, showing the superior creep resistance. Under low cycle fatigue loadings, the fatigue lifetimes of R and 2Cu alloys were similar, and slightly longer than that of 3.5Cu alloy. Conversely, in the high cycle fatigue regime, 3.5Cu alloy exhibited the highest fatigue resistance, followed by 2Cu and R alloys. The superior high-temperature performances of 3.5Cu alloy were attributed to the enhanced thermal stability of θ' precipitates compared to β' precipitates in R alloy, as confirmed during long-term thermal exposures at 250 and 300 °C. These findings suggest that 3.5Cu alloy is a promising candidate to replace the traditional A356 + 0.5Cu alloy for cylinder head applications.

Impact of block-loading on the high cycle fatigue strength of superalloy 617M at 973 K

The study demonstrates the positive influence of coaxing on the fatigue strength of alloy 617M under high cycle fatigue (HCF) loading at stress ratio (R) − 1, frequency ≈ 85 Hz, and temperature of 973 K. Tests were performed employing resonance excitation in two patterns viz., constant amplitude loading and block loading using a ‘low-to-high’ pattern. The fatigue limit for the constant amplitude loading pattern was determined to be 320 MPa for a runout criterion of 108 cycles. Upon under-stressing the alloy by application of a block loading pattern, the limit increased to 335 MPa. The increase of stiffness and associated resonance frequency during cycling indicated an initial hardening regime brought about by work hardening followed by a period of secondary hardening owing to precipitations occurring in the matrix. In the later stage, the frequency response also indicated the influence of dynamic strain ageing (DSA) on the alloy behaviour. Comparative microstructural characterisation of specimens is conducted to extend the understanding of coaxing and the resulting changes occurring in the work-hardening behaviour of the alloy.

Modified cure cycles for increased fatigue performance of fiber metal laminates

Modified (MOD) cure cycles that deviate from the manufacturer’s recommended cure profile can reduce the inherent thermally induced residual stresses (TRS) in fiber metal laminates (FML). Literature shows that MOD cycles do not adversely affect the material properties but enhance the quasi-static material strength. However, the literature does not comprehensively discuss the impact of MOD cycles on material performance during cyclic fatigue loading. This paper, therefore, investigates how MOD cycles influence the fatigue characteristics of different FML layups made of carbon fiber-reinforced polymer (CFRP) and steel. The experimental results confirm that the quasi-static material strength and the modulus of the FML are increased when using MOD cure cycles. The evaluation of fatigue tests with digital image correlation, thermography, and electrical resistance measurements of notched specimens shows that a reduction of TRS delays damage initiation in the metal facesheets and decreases the crack growth rate until facesheet failure. The results further show that layup-dependent parameters, the maximum stress in the metal sheets, and metal sheet thickness significantly govern the evolution of fatigue damage. In summary, modified cure cycles are an efficient tool to enhance the quasi-static and fatigue performance of CFRP-steel hybrid laminates.

Critical damage events of 3D printed AlSi10Mg alloy via in situ synchrotron X-ray tomography

Fish-scale-like melt pool structures and internal defects are characteristic features in additively manufactured (AM) metals. These play a critical role in the damage and fracture processes under different service loading conditions. However, the relationship between these damage features and loading conditions, as well as the spatial interactions between melt pool structures and internal defects remains poorly understood. Using in situ time-lapse synchrotron X-ray tomography and diffraction, we identify the initiation and growth events of life-limiting damage under tensile, low cycle fatigue (LCF), and high cycle fatigue (HCF) loading. A novel transition from meso-structure insensitive, defect-dominated short fatigue crack propagation to a meso-structure sensitive mechanism occurs as the plastic zone expands ahead of a growing crack from HCF to LCF to tensile loading. Under tension and LCF, the damage accumulation gradually increases and micro-voids nucleate at the melt pool boundaries (MPBs) after which the crack path follows the MPBs. In contrast, under HCF, surface defects initiate fatigue cracking and the MPBs have a very limited effect on the crack propagation path. Finally, a physics-informed machine learning method is introduced to develop a novel methodology for predicting fatigue life by including three-dimensional features of defects in AM parts.

An experimental-cohesive zone model approach to predict fatigue life of adhesive joints with varying modes of loading and joint configurations for automotive applications

ABSTRACT Predictive fatigue life models of adhesive joints are necessary to enable the assessment of automotive-bonded structures while reducing costly experimental testing. However, contemporary models have typically been calibrated for specific joint configurations and modes of loading, limiting their applicability to large-scale structures. Additionally, available models are based on simulation of cumulative fatigue cycling, making them computationally prohibitive. In the current study, cross-tension (CT) (load angles of 0°, 45°, and 90°) and single-lap shear joint (SLJ) configurations were bonded using an epoxy adhesive (BetaGuard CI6125R; PPG, France) used in automotive production (one part) and tested under fatigue cyclic loading. A total of nine joint configurations, having symmetrical (same material and thickness) and asymmetrical (dissimilar material or unequal thickness) joints, were tested. Fatigue tests at load levels between 25% and 75% of the static peak load were performed until joint failure or to runout (two million load cycles). The static tests of the joints were simulated to failure using finite element (FE) models with the cohesive zone method (CZM). The maximum strain energy release rates ( G max ) were calculated within the adhesive bond line at static loads corresponding to the peak loads of the fatigue tests. The G max values, computed from single cycle, specimen-specific FE simulations, were correlated with the measured fatigue life ( N f ) of the adhesive joints with varying modes of loading and joint configurations. The fatigue life prediction model, based on G max − N f correlation and following a crack propagation approach, predicted the cycles to failure for 85% of the fatigue tests, and 81% of the independent validation tests. The proposed fatigue life prediction approach provides computational efficiency and large-scale compatibility.

Comparison of Percutaneous Lapidus Intra Osseous Screws vs Open Plate Fixation for First Tarsometatarsal Fusion: A Matched Cadaver Study

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Foot and ankle joint fusion fixation traditionally uses bridging plates or compression screws. However plates require incisions unsuitable for percutaneous surgery. Therefore in creating a percutaneous Lapidus procedure a new form of fusion fixation was designed. The concept preserves subchondral bone after complete cartilage removal. Fixation is with intra osseus full thread non variable pitch screws. The purpose of this study was to compare the biomechanical properties of the open plate and cross screw construct vs. the percutaneous construct. The cadaveric study goal was to compare the cycles to failure, load to failure and stiffness of each fixation type, and the plantar gap measured during each cycle throughout the test. Loading conditions replicated 6 weeks of walking in a short-leg walking cast. Methods: The TMT joint of six matched cadaveric legs were fixated with a Lapidus procedure: Six limbs with a locking plate and 3.5 mm cross compression lag screw (“plated treatment”) and six with a percutaneous Lapidus procedure, preserving subchondral bone (“MIS treatment”). The three medial metatarsals, cuneiforms, and the navicular were excised from each cadaveric limb and potted, with the TMT joint exposed ~1 cm, then frozen. Specimens were thawed, an extensometer was placed on the plantar side of the TMT, and the 1st metatarsal was loaded 5 cm distal to the TMT joint, from 9N to 90N compression at 3 Hz. Testing was stopped if the extensometer reached 7 mm of plantar gap, or 250,000 cycles were reached. Following fatigue loading, specimens were statically loaded to failure. The maximum load and stiffness were recorded. Bone screw pullout strength and compressive modulus of the distal metatarsal were measured. Results: MIS-treated specimens reached significantly-higher cycles to failure (221,452 cycles) compared to plate-treated specimens (34,941 cycles). Plantar gap was significantly higher at all cycle counts from 10 to 10000 cycles (> 4mm) in the plate-treated group than in the MIS-treated group ( < 1 mm). The maximum load observed in the cantilever static test following fatigue testing was significantly higher in the MIS-treated group (343.3 N) compared to the plate-treated group (247.3 N). The stiffness of the MIS-treated group was also significantly higher than the plate treated group (40.9 N/mm vs 16.0 N/mm). No statistical differences in the screw pullout strength nor compressive modulus were observed. A Cox Proportional Hazard model identified the mode of fixation as the only significant covariant (p=0.03) when predicting cycles-to-failure. Conclusion: Our data indicate the percutaneous Lapidus construct had significantly lower plantar gap during cyclic loading, higher load-to-failure following cyclic loading, higher stiffness, and higher number of cycles required to reach 7 mm of displacement compared to the plate. The implant type (MIS or Plate) was the only covariant which predicted fatigue loading cycles to failure. Stratifying the baseline hazards by implant type in the hazard model, no other covariant reached statistical significance. The percutaneous subchondral fixation fusion construct with full thread non variable pitch intraosseous screws allows stronger fixation than traditional plates and cross screws.

Study on hysteresis behavior of two kinds of reinforced CHS X-joints

Ultra-low cycle fatigue loading tests were conducted on two reinforced CHS X-joints (external stiffening rings and plates) and an unreinforced joint to analyze their post-yield failure modes, fracture mechanisms, and hysteretic properties. The findings indicate that these three joints exhibit varying failure modes post-yield: the unreinforced joints fail primarily due to chord fracture at the weld; the ring-reinforced joints initially see ring fracture, followed by chord crack at the weld; while the plate-reinforced joints initially fail from chord fracture and subsequently develop cracks at the plate-chord interface. The reinforced joints display plumper hysteretic loops and higher ultimate bearing capacities than the unreinforced joint. Compared to X-1, the tensile and compressive ultimate bearing capacities of RX-1 have increased significantly by 56.9 % and 74.1 %, respectively. In comparison, those of TX-1 have increased moderately by 2.2 % and 67.6 %, respectively, albeit with a slight compromise in ductility. The cumulative energy dissipation of RX-1 and TX-1 has risen by 22.62 % and 131.99 %, respectively, compared to the unreinforced joint. Notably, the dissipated energy before cracking accounts for 16.50 %, 18.16 %, and 22.29 % of the cumulative energy dissipationfor the three joints, respectively, highlighting the substantial contribution of crack propagation to energy dissipation under large deformations. The VUSDFLD subroutine based on Cyclic Void Growth Model (CVGM) is embedded into ABAQUS, this subroutine considers the initiation and propagation of joint cracks. Three finite element models with the same dimensions of the specimens were built to simulate the damage process of the joint. The results show that this method can accurately simulate such joints’ cracking and crack growth behavior under cyclic axial load. The simulated hysteresis curve is in good agreement with the test curve.

The Effects of Mechanical Loading on Resonant Response of a Conformal Load-Bearing Antenna System.

Glass fibre-reinforced polymer (GFRP) is a suitable substrate material for constructing a Conformal Load-Bearing Antenna Structure (CLAS). The relative permittivity of the CLAS substrate, which determines its resonant frequency, is affected by damage sustained by GFRP. This paper investigates the effects of damage (induced by mechanically loading the substrate) on the resonant response of the CLAS. Decoupling the antenna from the substrate was essential to evaluate the CLAS's true response to the induced damage. This paper details a systematic investigation examining how the frequency response of a "pristine" antenna and a surface-mounted antenna respond to a substrate subjected to quasi-statically induced mechanical damage and cyclic fatigue loading. The results demonstrate that the resonant frequency of the CLAS varies as a function of the substrate's mechanical damage. The prepared CLAS is tolerant to a certain degree of mechanical loading and related damage with its resonant frequency remaining within an acceptable bandwidth.