Applied Loading Conditions Research Articles

Effect of Applied Loads on Water and Chloride Penetrations of Strain Hardening Cement-Based Composites

AbstractStrain-hardening cement-based composites (SHCC) with polyvinyl alcohol (PVA) fibers have excellent tensile and bending behaviors; however, their water and aggressive ion penetrations should be considered carefully under applied load conditions because they can significantly influence the durability of SHCC. The goal of this study is to evaluate the effect of applied loads on water and chloride penetrations of SHCC. The capillary absorption test was respectively carried out under loading and after unloading, and then the water and chloride penetrations were evaluated. The results show that applied loads have a significant effect on penetrations, and the penetrations prove to rise with the increase of applied loads. Particularly, when a higher load is applied, water and chloride rapidly penetrate into SHCC. However, SHCC-W whose surface is processed with waterproofing agent, exhibits good penetration resistance. Due to the shrinkage stress induced by fibers in SHCC, the crack widths of SHCC after un...

Permeability behavior of integral water-repellent SHCC under applied load conditions

Strain-hardening cementitious composite (SHCC) with PVA fibers possesses a predominant tensile and bending strength. However, attributing to the existence of fibers in SHCC, the high strain is frequently appeared under different applied load conditions. More cracks are formed with the increase in strain, which significantly increases the permeability of SHCC. Mixing silane emulsion into fresh SHCC can prepare integral Water-Repellent SHCC (IWR-SHCC), and it is an effective method for improving the durability and permeability resistance of SHCC. This investigation aims to evaluate the permeability of IWR-SHCC under different applied load conditions. The capillary absorption test is used in this paper to evaluate the permeability behavior of IWR-SHCC. The capillary absorption test was carried out under loading and after unloading, and the water and chloride penetrations were measured. The results show that applied loads have a significant impact on the permeability behavior of IWR-SHCC, and the permeability is proved to increase with the increasing applied loads, and increases with the increase in curing time. Compared to the permeability behavior of SHCC, IWR-SHCC has better permeability resistance under the same applied load condition. Preparing IWR-SHCC is an effective way to improve the permeability resistance of SHCC under applied load condition.

Abrasion wear behavior of a forged and unforged Fe-B alloy

Abstract Fe-B alloys exhibit continuous networks of eutectic borides, which destroy the continuity of matrix and result in the brittleness of the material. In order to improve its toughness, Fe-B alloy was treated by hot forging process in this study. Three-body abrasion wear behaviors of forged and unforged Fe-B alloy under three different abrasive (SiC, garnet and quartz sand) and applied load conditions were studied. Wear mechanisms were investigated by using scanning electron microscope (SEM) and 3D laser scanning microscope (LSM). The result shows that under three-body abrasion condition, Fe-B alloy exhibits excellent wear resistance. The wear resistance of forged samples is higher than that of unforged samples on the three different kinds of abrasive. A correlation between the hardness of the abrasive, movement patterns of abrasive particles and applied load was found. The movement patterns of quartz sand are sliding between the contacting surfaces under the load of 3 kg. In the wear process of Fe-B alloy, sliding/cutting is the dominant removal mechanism in the case of quartz sand abrasive and rolling is the dominant removal mechanism in the case of garnet abrasive during three-body abrasion under the load of 3 kg. When Fe-B alloys are tested under the load of 1, 3 and 5 kg, it is found that load can change the movement patterns of abrasive particles. With increasing load, the movement patterns of abrasive particles are changed from rolling to sliding mechanism. Our investigations reveal that the three-body abrasive wear mechanism of forged and unforged Fe-B alloy depends on material/abrasive hardness ratio and applied load.

Numerical simulation of crack propagation under fatigue loading in piezoelectric material using extended finite element method

Piezoelectric materials due to their electromechanical coupling characteristics are being widely used in actuators, sensor, transducers, etc. Considering wide application it is essential to accurately predict their fatigue and fracture under applied loading conditions. The present study deals with analysis of fatigue crack growth in piezoelectric material using the extended finite element method (XFEM). A pre-cracked rectangular plate with crack at its edge and center impermeable crack-face boundary conditions is considered for simulation. Fatigue crack growth is simulated using extended finite element method under plane strain condition and mechanical, combined (mechanical and electrical) cyclic loading. Stress intensity factors for mechanical and combined (mechanical and electrical cyclic loadings) have been evaluated by interaction integral approach using the asymptotic crack tip fields. Crack propagation criteria have been applied to predict propagation and finally the failure.

Three-dimensional cracked discs under anti-plane loading and effects of the boundary conditions

Purpose– Accordingly to the recent multi-scale model proposed by Sih and Tang, different orders of stress singularities are related to different material dependent boundary conditions associated with the interaction between the V-notch tip and the material under the remotely applied loading conditions. This induces complex three-dimensional stress and displacement fields in the proximity of the notch tip, which are worthy of investigation. The paper aims to discuss these issues.Design/methodology/approach– Starting from Sih and Tang’s model, in the present contribution the authors propose some analytical expressions for the calculation of the strain energy density (SED) averaged over a control volume embracing the V-notch tip. The expressions vary as a function of the different boundary conditions. Dealing with the specific crack case, the results from the analytical frame are compared with those determined numerically under linear-elastic hypotheses, by applying different constraints to the through-the-thickness crack edges in three-dimensional discs subjected to Mode III loading. Free-free and free-clamped cases are considered.Findings– Due to three-dimensional effects, the application of a nominal Mode III loading condition automatically provokes coupled Modes (I and II). Not only the intensity of the induced modes but also their degree of singularity depend on the applied conditions on the crack flanks. The variability of local SED through the thickness of the disc is analysed by numerical analyses and compared with the theoretical trend.Originality/value– The capability of the SED to capture the combined three-dimensional effects is discussed in detail showing that this parameter is particularly useful when the definition of the stress intensity factors (SIFs) is ambiguous or the direct comparison between SIFs with odd dimensionalities is not possible.

The effects of long-range residual stress, elastic follow-up and applied load on creep crack incubation and material toughness

Creep crack incubation of Type 316H stainless steel at 550 °C is explored in this article. Fracture mechanics specimens, subjected to combinations of residual and applied loads and in the presence of elastic follow-up, are tested. The design of two new test rigs is described. The rigs introduce planned levels of elastic follow-up together with combined residual and applied loading conditions to the specimens. A series of high-temperature elastic–plastic and elastic–plastic–creep experiments are undertaken to compare the experimentally determined values of elastic follow-up with the theoretical values. A further series of fracture mechanics tests are performed to measure creep crack incubation and material toughness for samples subjected to constant load and for tests under combined loading with elastic follow-up. It is demonstrated that for tests subjected to the same initial reference stresses, longer incubation times are attained for elastic follow-up tests compared to constant load tests. Also, combined loading tests exhibit longer creep crack incubation times based on the same measured material toughness obtained from constant load tests. This suggests that not all the available strain energy provided by combined loading to a specimen at high temperature contributes to creep crack incubation.

On the monitoring and implications of growing damages caused by manufacturing defects in composite structures

Damage tolerance is a classical safety concept for the design of aircraft structures. Basically, this approach considers possible damages in the structure, predicts the damage growth under applied loading conditions and predicts the following decrease of the structural strength. As a fundamental result the damage tolerance approach yields the maximum inspection interval, which is the time a damage grows from a detectable to a critical level. The above formulation of the damage tolerance safety concept targets on metallic structures where the damage is typically a simple fatigue crack. Fiber-reinforced polymers show a much more complex damage behavior, such as delaminationsin laminated composites. Moreover, progressive damage in composites is often initiated by manufacturing defects. The complex manufacturing processes for composite structures almost certainly yield parts with defects, e.g. pores in the matrix or undulations of fibers. From such defects growing damages may start after a certain time of operation.The demand to simplify or even avoid the inspection of composite structures has therefore led to a comeback of the traditional safe-life safety concept. The aim of the so-called safe-life flaw tolerance concept is a structure that is capable of carrying the static loads during operation, despite significant damages and after a representative fatigue load spectrum. A structure with this property does not need to be inspected, respectively monitored at all during its service life. However, its load carrying capability is thereby not fully utilized.This article presents the possible refinement of the state-of-the-art safe-life flaw tolerance concept for composite structures towards a damage tolerance approach considering also the influence of manufacturing defects on damage initiation and growth. Based on fundamental physical relations and experimental observations the challenges when developing damage growth and residual strength curves are discussed.

An analytical method for predicting the anti-plane effective magnetoelectroelastic coefficients of composites containing doubly periodic multicoated fibers

The present paper deals with the magnetoelectroelastic composites containing a doubly periodic array of multicoated fibers under anti-plane shear loads and in-plane electromagnetic loads. By introducing the generalized eigenstrain, the heterogeneous magnetoelectroelastic medium is equivalent to a homogeneous magnetoelectroelastic medium with the periodically distributed generalized eigenstrains. Then the homogeneous magnetoelectroelastic medium with the generalized eigenstrain is solved analytically under the applied load conditions, the generalized stresses and strains in the fibers, coatings and matrix are derived. Based on the average-field theory, the solutions of the generalized stresses and strains are applied to determine the anti-plane effective magnetoelectroelastic properties of the composites. Two-phase (fiber/matrix) and three-phase (fiber/coating/matrix) magnetoelectroelastic composites are examined, and the comparison between the obtained results and the existing results shows the accuracy of the proposed method. Several four-phase magnetoelectroelastic composites with epoxy matrix are studied, and the influences of the composites microstructures on the effective magnetoelectric coefficient are discussed.

Design-oriented strength of mechanical joints in composite laminate structures and reliability-based design factor

Mechanical joints may act as bottlenecks in the design process of composite structures. Fitting factors need to be multiplied with the applied load condition to assure reliability. For more efficient design, this paper proposes a brand-new design-oriented strength: knee point strength for the mechanical joints in composite laminates. The knee point strength is derived from the stiffness change rate for the bearing stress–strain behavior in a bearing test. The strength can be correlated with the internal bearing damage; this is verified by micrography about the bearing test specimen and finite element analysis. The probabilistic design and analysis method was applied to acquire the reliability-based fitting factor. An approach combining finite element damage analysis and a stochastic technique was adopted to analyze the probabilistic properties for the design-oriented strength of the bolted joints in CFRP laminates. The probabilistic and deterministic designs were compared and discussed. Then a proper value of the fitting factor was proposed.

Numerical investigation of FAST powder consolidation of Al2O3 and additive free β-SiC

In this work we examine ceramic synthesis through powder consolidation and the field assisted sintering technique. In particular, we investigate the sintering of Al2O3 and additive free from both an experimental and numerical perspective. For the numerical model, the continuum theory of sintering model is employed, and the densification mechanisms corresponding to power law creep and grain boundary diffusion are considered. Experiments are used for comparison and validation purposes. The results indicate that in general, the densification kinetics simulated by the numerical model compare favorably with the experimental results. Parametric studies involving initial grain size, heating rate, and applied stress are also examined using the numerical model, and confirm many of the expected results from previous research, including increased densification due to higher heating rates, smaller grain sizes, and increased applied loading conditions.

10517 ガラスのホイール割断における亀裂進展挙動の高速度カメラ観察

The crack propagation behavior was observed by high-speed camera during wheel scribing of non-alkali glass sheet. As a result, it was found that the propagation depth was largely influenced by the applied load to scribing wheel. In the case of glass sheet of 0.7 mm thickness, for example, a formed crack rapidly propagated to the depth direction when the applied load was 20 N. On the other hand, when the applied load was 10 N, a formed crack hardly propagated. In order to investigate the reason of difference between crack propagation behaviors, high-speed birefringence measurements were also conducted. The measurement from above of glass sheet showed that the characteristic patterns appeared in phase difference diagram depending on the applied load conditions.

Interactive creep–fatigue crack growth of 2024‐T3 Al sheets: selective transitional functions

AbstractInteractive creep–fatigue on aeronautical materials has been of a great concern to engineers and researchers. There are still more fundamental issues to be addressed. In this regard, 2024‐T3 Al sheets are considered to study the transitional behaviours that incorporatematerial, loading and geometry effects in the interactive creep–fatigue process. A dual‐scale fatigue crack growth da/dN‐ΔS model that includes microscale, macroscale and large scales is proposed based on the volume energy density criterion. The model generates the transitionalised crack length (TCL) compared with the fictitious crack length (FCL) yielded from the da/dN‐ΔK model that is only restricted to monoscaling. Crossover points are observed across TCL and FCL curves. With stress amplitude being fixed, three levels of mean stress are employed to discuss the variational effects of transitional functions (TFs). Applied loading conditions have an appreciable effect on the fatigue life cycles of 2024‐T3 Al sheets. Variation of R ratios leads to the interactive creep–fatigue behaviour and further enforces the selective TFs in the inherent multiscaling process. TCLs and FCLs are compared with test data of the 2024‐T3 Al sheet. Rationality and superiority of the dual‐scale crack growth model are validated.

The effects of different boundary conditions on three-dimensional cracked discs under anti-plane loading

Abstract Accordingly to the recent multi-scale model proposed by Sih and Tang, different orders of stress singularities are related to different material dependent boundary conditions associated with the interaction between the V-notch tip and the material under the remotely applied loading conditions. This induces complex three-dimensional stress and displacement fields in the proximity of the notch tip, which are worthy of investigation. Starting from Sih and Tang's model, in the present contribution the authors propose some analytical expressions for the calculation of the strain energy density (SED) averaged over a control volume embracing the V-notch tip. The expressions vary as a function of the different boundary conditions. Dealing with the specific crack case, the results from the analytical frame are compared with those determined numerically under linear-elastic hypotheses, by applying different constraints to the through-the-thickness crack edges in three dimensional discs subjected to Mode III loading. Free–free and free–clamped cases are considered. Due to three-dimensional effects, the application of a nominal Mode III loading condition automatically provokes coupled Modes (I and II). Not only the intensity of the induced modes but also their degree of singularity depend on the applied conditions on the crack flanks. The variability of local SED through the thickness of the disc is investigated by numerical analyses and compared with the theoretical trend. The capability of the SED to capture the combined three-dimensional effects is discussed in detail showing that this parameter is particularly useful when the definition of the Stress Intensity Factors (SIFs) is ambiguous or the direct comparison between SIFs with odd dimensionalities is not possible.

On void shape effects of periodic elasto-plastic materials subjected to cyclic loading

Abstract This work investigates the effect of cyclic loading upon periodic elasto-plastic porous materials. The aim is to understand the evolution of the underlying microstructure, described here with a single void embedded in a cubic unit-cell. Periodic finite element (FEM) calculations are carried out under a finite strain deformation process keeping the absolute value of the stress triaxiality and the Lode angle constant during the cycle. As a result of the applied loading conditions, the void geometry, both volume and shape, change significantly leading to porosity and void shape ratcheting. The void shape becomes non-spherical from the very first cycle leading to a markedly asymmetric cyclic response of the material. This, in turn, results in an observed maximum stress as a function of the number of cycles. In addition, even though the average applied strains are relatively small, the local strains near the void surface increase significantly inducing a significant localization of the deformation. Finally, several initial void shape configurations are also considered. In the majority of the cases studied, the void evolves into a crack-type shape in the direction of the minimum absolute stress. This, in turn, is consistent with a configuration corresponding to a crack subjected to a mode I cyclic loading.

A Direct Method on the Evaluation of Cyclic Steady State of Structures With Creep Effect

This paper describes a new extension of the linear matching method (LMM) for the direct evaluation of cyclic behavior with creep effects of structures subjected to a general load condition in the steady cyclic state, with the new implementation of the cyclic hardening model and time hardening creep constitutive model. A benchmark example of a Bree cylinder and a more complicated three-dimensional (3D) plate with a center hole subjected to cyclic thermal load and constant mechanical load are analyzed to verify the applicability of the new LMM to deal with the creep fatigue damage. For both examples, the stabilized cyclic responses for different loading conditions and dwell time periods are obtained and validated. The effects of creep behavior on the cyclic responses are investigated. The new LMM procedure provides a general purpose technique, which is able to generate both the closed and nonclosed hysteresis loops depending upon the applied load condition, providing details of creep strain and plastic strain range for creep and fatigue damage assessments with creep fatigue interaction.

Computational analysis of nonlinear creep of polyphase aggregates: Influence of phase morphology

AbstractThe constitutive laws of polyphase aggregates dominantly depend on the operative deformation mechanisms, phase morphology and modes, and environmental conditions. Each of these factors has the potential to dramatically affect bulk mechanical properties as well as the local stress and strain rate distributions. To focus on the effects of phase morphology, we have developed a rigorous multiscale approach based on asymptotic expansion homogenization. The proposed methodology has two fundamental goals: (1) accurately predict bulk behavior in aggregates by explicitly taking into account phase morphology and (2) calculate detailed distributions of strain rates, stresses, and viscosities in heterogeneous materials. The methodology is able to consider general nonlinear phase constitutive laws that relate strain rates to stresses, temperature, and other factors such as water fugacity and grain size. We demonstrate the approach by analyzing power law creep of computer‐generated and natural polyphase systems and benchmarking the results against analytical solutions. As an outcome of this analysis, we find that the approximation of an aggregate as a power law material is reasonable for isotropic, homogeneous phase distributions but breaks down significantly with high degrees of phase organization. We also present distributions in strain rate, stress, and viscosity for different applied loading conditions. Results exhibit areas of high internal stresses and substantial localization. We describe and provide a freely available software package supporting these calculations.

Failure modes and fracture toughness in partially torn ligaments and tendons

Ligaments and tendons are commonly torn during injury, yet the likelihood that untreated initial tears could lead to further tearing or even full rupture has proven challenging to predict. In this work, porcine Achilles tendon and human anterior longitudinal ligament samples were tested using both standard fracture toughness methods and complex loading conditions. Failure modes for each of 14 distinct testing cases were evaluated using a total of 131 soft tissue tests. Results showed that these soft tissues were able to completely resist any further crack propagation of an initial tear, regardless of fiber orientation or applied loading condition. Consequently, the major concern for patients with tendon or ligament tears is likely not reduction in ultimate tissue strength due to stress risers at the tip of the tear, but rather a question of whether or not the remaining cross-section is large enough to support the anticipated loading.

Numerical Simulations of Longitudinal Elastic Behavior of Single-Walled Carbon Nanotubes–Reinforced Polymer Nanocomposites

AbstractThe longitudinal elastic behavior of single-walled carbon nanotubes (SWCNTs) and SWCNT reinforced polymer nanocomposites are investigated. Finite-element (FE) models of SWCNTs and SWCNT reinforced polymer nanocomposites are developed utilizing a multiscale modeling technique along with molecular structural mechanics (MSM), which provides material properties at a molecular scale and establishes relations between the steric potential energy and classic structural mechanics. The mechanical behavior of SWCNT reinforced polymer nanocomposites is dictated by the mechanical behavior of the SWCNTs embedded in the polymer matrix. Furthermore, varying the radius and length of the SWCNTs affects the longitudinal elastic properties of the SWCNT reinforced polymer nanocomposites. Specifically, the simulation results demonstrated that longitudinal elastic properties of SWCNT reinforced polymer nanocomposites would vary due to different applied loading conditions, i.e., discrete and continuous.

Application of an extended Rusinek–Klepaczko constitutive model to predict the mechanical behavior of 6082-T6 aluminum under Taylor impact test conditions

The application of an extended Rusinek–Klepaczko constitutive equation to predict the mechanical response of 6082-T6 aluminum under the Taylor impact test conditions was presented in this article. The numerical results obtained in the study were verified through a comparison with the experimental data extracted from the Taylor anvil-on-rod impact experiments. It was concluded that the extended Rusinek–Klepaczko constitutive model predicts the behavior of the tested aluminum alloy under applied loading conditions with satisfactory accuracy. Moreover, it was found that the plastic wave phenomenon in this material is very limited and that there was no region of constant plastic wave velocity. Strain rates up to 1.6 × 104 s−1 were recorded during the Taylor impact experiments; therefore, this value may be set as the upper limit of the extended Rusinek–Klepaczko model for the alloy, which was validated with the anvil-on-rod experiment.

Crack path evaluation on HC and BCC microstructures under multiaxial cyclic loading

In this paper the multiaxial loading path effect on the fatigue crack initiation, fatigue life and fracture surface topology are evaluated for two different crystallographic microstructures (bcc and hc): high strength low-alloy 42CrMo4 steel and the extruded Mg alloy AZ31B-F, respectively.A series of multiaxial loading paths were carried out in load control, smooth specimens were used. Experimental fatigue life and fractographic results were analyzed to depict the mechanical behavior regarding the different microstructures.A theoretical analysis was performed with various critical plane models such as the Fatemi–Socie, SWT and Liu in order to correlate the theoretical estimations with the experimental data. A new approach based on maximum stress concentration factors is proposed to estimate the crack initiation plane, estimations from this new approach were compared with the measured ones with acceptable results. To implement this new approach a virtual micro-notch was considered using FEM. Moreover, the multiaxial loading path effect on stress concentration factors is also studied. The obtained results clearly show the effect of the applied load conditions on local microstructures response.