Presence Of Cyclic Loading Research Articles

The condition of chemical properties in the soil on the liquefied land in Jono Oge Village, Sigi Regency, Central Sulawesi

Liquefaction is an event in which the soil loses shear strength due to increased pore water stress by the presence of cyclic loading. As a result of this incident, a number of paddy fields and housing estates in Jono Oge village experienced liquefaction. There is mud vomiting and the movement of a number of soils, causing eroded areas and some of them experiencing hoarding Research aims to identify the chemical properties of soils affected by liquefaction. The study was conducted using the survey method, soil sampling was carried out by purposive sampling. Soil samples were taken on three categories of affected land: eroded land, landfilled land, and surrounding land that was not liquefied. The results showed that the areas affected by liquefaction in the three categories of land had a soil pH relative to the same criteria, namely neutral (pH 6.52-6.77). Then C-organic levels in both eroded and hoarding fields are moderate status (2.50-2.70%) and in non-liquefied lands is low status (1.52%), while N-Total all three have low status (0.12-0.19%). Sodium content is generally medium status (0.41-0.60 me/100g), Calcium is generally high status (11.88-13.42 me/100g) and Magnesium is generally moderately. This research was conducted after more than 2 years of liquefaction and the most affected soil chemical properties in the respected area is the increasing of C-organic content.

Fatigue of Shape Memory Alloys With Emphasis on Additively Manufactured NiTi Components

Abstract Shape memory alloys (SMAs) are often used in applications involving time-varying loads. Under such conditions, fatigue leading to possible fracture is a paramount cause of failure, which has been extensively investigated since the 1960s. This work reviews developments in this field with emphasis on recent results related to additively manufactured SMAs. Multiple factors influencing structural and functional degradation in presence of cyclic loading are considered, including microstructural and surface features, thermal loading history, and heat treatment. For completeness, select modeling approaches proposed in the literature to predict SMA fatigue are briefly overviewed and a discussion is provided on the statistical relevance and uncertainty of published data. Conclusions are then formulated to guide subsequent research.

A coupled critical plane-[formula omitted] methodology to estimate fatigue life for an AISI 1045 steel with small artificial defects

The presence of notches, tears, holes, cavities, inclusions, and scratches is common in structural designs and mechanical components, that in the presence of cyclic loading can influence their resistance and fatigue life. The objective of this research is to propose and validate an approach for fatigue life estimation for materials with small defects subjected to combined loading. The approach of the project is formulated based on a calibration strategy for Fatemi-Socie, Smith-Watson-Topper and Susmel and Lazarin critical plane models, using Murakami criteria and notch factor to compute the defect effect. The results predicted by the model were compared and validated with experimental data, showing it to be a promising strategy. For further extension and a more generalized application of the proposed model, it is necessary to perform life prediction comparisons for different materials, loadings, and defect geometries.

Development of a constitutive model considering functional fatigue and pre-stretch in shape memory alloy wires

Shape memory alloy (SMA) wires integrate functionality into composites and encourage the design and creation of adaptable smart structures. Upon the application of cyclic loading, however, the functional properties of SMA wires can decrease significantly resulting in functional fatigue. To simulate this cyclic behavior, an SMA material model with logarithmically evolving and temperature dependent functional fatigue is developed. Pre-stretch is also considered to simulate structures with embedded pre-stretched SMA wires. The material model is fit to a set of tests (constant strain, isobaric, isothermal tension, isothermal cyclic tension) performed on SMA wires. The fit demonstrates an excellent agreement with the experimental results with minor discrepancies. The simulations show the capabilities of the model to evolve the residual strains, residual stresses, hysteresis and hardening in the presence of cyclic loading. Additionally, the isobaric actuation behavior and the reorientation response of the model are validated using experiments from the literature. The fitted and validated model is then used to simulate the response of a rubber specimen with two embedded SMA wires subjected to cyclic thermal loading. The simulated rubber specimen illustrates the loss of functionality after the applied cyclic loading and highlights the importance of not exceeding design temperature loads. Furthermore, the complex thermomechanical loading in the SMA wires displays the importance of including temperature or stress dependence for defining functional fatigue.

Analysis of the influence of microstructural traps on hydrogen assisted fatigue

We investigate the influence of microstructural traps on hydrogen diffusion and embrittlement in the presence of cyclic loads. A mechanistic, multi-trap model for hydrogen transport is developed, implemented into a finite element framework, and used to capture the variation of crack tip lattice and trapped hydrogen concentrations as a function of the loading frequency, the trap binding energies and the trap densities. We show that the maximum value attained by the lattice hydrogen concentration during the cyclic analysis exhibits a notable sensitivity to the ratio between the loading frequency and the effective diffusion coefficient. This is observed for both hydrogen pre-charged samples (closed-systems) and samples exposed to a permanent source of hydrogen (open-systems). Experiments are used to determine the critical concentration for embrittlement, by mapping the range of frequencies where the output is the same as testing in inert environments. We then quantitatively investigate and discuss the implications of developing materials with higher trap densities in mitigating embrittlement in the presence of cyclic loads. It is shown that, unlike the static case, increasing the density of “beneficial traps” is a viable strategy in designing alloys resistant to hydrogen assisted fatigue for both closed- and open-systems.

Structural integrity of additively manufactured stainless steel with cold sprayed barrier coating under combined cyclic loading

Integration of metal additive manufacturing (AM) and cold spray (CS) technologies provide an unprecedented opportunity to manufacture coated material systems with complex geometrical features. The application of these material systems in functionally critical components requires adequate structural integrity, particularly in the presence of cyclic loading. This work researches the multiaxial fatigue (axial-torsional cyclic loading) behavior of a coated material system consisting of 15Cr-5Ni precipitation-hardening stainless steel (15-5 PH SS) substrate additively manufactured by direct metal laser sintering with a layer of chromium carbide nickel (CrC-Ni) barrier coating deposited by CS. The influence of AM and CS-induced residual stresses on fatigue performance of test specimens was thoroughly studied. Additionally, the effect of surface roughness and processes induced defects were considered to explain the crack growth mechanism. Stresses assessed by synchrotron X-ray diffraction indicated a substantial accumulation of residual stresses, particularly in the outer surface of the as-fabricated 15-5 PH SS specimens. The state of residual stress was changed notably following the deposition of CrC-Ni coating in the axial, hoop, and radial directions of the fatigue test specimen. Also, CS deposition of CrC-Ni coating caused significant improvement in the surface quality of the additively manufactured components. Fatigue test results indicated, CS deposition of CrC-Ni substantially enhances the fatigue life of the AM-produced 15-5 PH SS substrate in all loading conditions, particularly in the high cycle fatigue regime. The improvement in the fatigue life of the specimens with coating was associated with a reduction in equivalent residual stress at the substrate surface and improvement in the specimens' surface condition (i.e., reduced surface roughness). The fractographic analysis of the specimen indicated the cracks tend to initiate in the surface of both as-fabricated and cold-sprayed specimens. However, the mechanism of crack growth changed notably following the deposition of CrC-Ni coating. The cracks tended to propagate in the planes parallel or with a small deviation from the build layers of the AM-produced specimens. On the other hand, deposition of CrC-Ni coating increased the deviation of crack growth plane from the build layers of the substrate.

Fatigue Crack Growth in Maraging Steel Obtained by Selective Laser Melting

Selective Laser Melting (SLM) is an additive manufacturing technology, ideal for the production of complex-shaped components. Design against fatigue is fundamental in the presence of cyclic loads, particularly for these materials which typically have significant porosity, high surface roughness and residual stresses. The main objective here is to study fatigue crack growth (FCG) in the 18Ni300 steel obtained by SLM. Typical da/dN-ΔK curves were obtained in C(T) specimens, indicating that cyclic plastic deformation may be the controlling mechanism. A complementary analysis, based on plastic CTOD range, showed a relatively low level of crack tip plastic deformation, and consequently a reduced level of plasticity induced crack closure. The curve da/dN versus plastic CTOD range is clearly above the curves for other materials.

Closed-form solutions for one-dimensional consolidation in saturated soils under different waveforms of time-varying external loading

A set of closed-form series solutions that account for the transient and steady-state responses of excess pore water pressure and total settlement to one-dimensional consolidation in saturated soils exposed to various typical types of time-dependent external loading with any desired excitation amplitude and period is symmetrically formulated based on the theory of poroelasticity. The mathematical approach developed in the current study is quite general so that it can be straightforward extended to arbitrary waveform shapes of harmonic loading after they are simply represented in terms of Fourier trigonometric series. These solutions are numerically calculated to evaluate variations in excess pore water pressure and total settlement due to vertical consolidation in saturated soils with two very different magnitudes of intrinsic permeability, Soil A (higher) and Soil B (lower), as representative examples using two illustrative periods per cycle. Our results show that within excitation frequencies we examined, the excess pore water pressure exhibits greater cyclic swings in Soil B than that in Soil A as harmonic stress compression and relaxation are added, but an inverse trend is observed for total settlement. As compared to static external loading, the excess pore water pressure persists longer with periodic fluctuation in the presence of cyclic loading, but less total settlement is induced in Soil B. The discrepancy in the latter (total settlement) between the static and cyclic loading is most significant in Soil B, reflecting a physical implication that low permeability leads to a slower dissipation of excess pore water pressure, thus causing less settlement with time.

Effect of Cyclic Strain on the Mechanical Behavior of a Thermoplastic Polyurethane

Thermoplastic polyurethanes (TPUs) are polymeric materials employed in a wide array of applications in the industrial field. Knowledge of their mechanical behavior is essential in order to obtain an accurate prediction of stresses and deformations resulting from loading. Mechanical and physical properties of these materials have been studied in the past, but their stress-strain behavior in the presence of cyclic loading has comparatively received much less attention. In this paper, experimental and constitutive modeling aspects concerning cyclic mechanical response of a TPU are investigated. The effect of imposing a cyclic strain on a TPU is studied by means of an experimental procedure based on alternate-symmetric tests in strain control at different strain levels and frequencies. During the tests, the increase in temperature due to the hysteretic heating can also be controlled by means of a compressed air cooling apparatus specifically devised. By taking advantage of the possibility of controlling and stabilizing temperature, the cyclic mechanical response can then be investigated at different temperatures and strain levels. A transient thermal analysis using finite element method (FEM) was also carried out to investigate temperature distribution on the specimen. TPU exhibited cyclic softening, and by comparing stabilized material response at different temperatures, cyclic softening was shown to be composed of a mechanical contribution and a thermal component. The TPU’s stress-strain curve changed considerably under cyclic loading conditions. In particular, cyclic softening was observed to increase with temperature and imposed cyclic strain, with a progressive shrinking of hysteresis loop passing from virgin condition to stabilized cyclic condition. Based on the experimental data, the cyclic curve could be determined as a function of temperature and could be fitted with a hyperelastic law in which material parameters are temperature dependent. The TPU exhibited significant sensitivity to cyclic loading, and this study demonstrated the importance of considering mechanical response in cyclic condition for design purposes. In particular, the identification of mechanical and thermal contributions to cyclic softening can be useful when studying fatigue failure mechanisms of these materials. Knowledge of cyclic curve can help when developing constitutive model for polymers to better predict a long-term behavior when cyclic loading is expected. The introduction of a dependence of cyclic curve on temperature allows considering simultaneously the new “material state” of the cycled polymer and, with some limitations, the thermal influence on mechanical response.

Anomalous debonding behavior of a polymer/inorganic interface

Adhesion and subcritical debonding at the interface between a thin diglycidyl ether of bisphenol F polymer layer and either SiN x or SiO 2 passivated silicon substrates are described. The interface is characterized by weak hydrogen bonding. Prolonged exposure to a moist environment resulted in a time-dependent decrease in adhesion. Subcritical debond-growth rates as a function of applied loads were sensitive to temperature and relative humidity, and greatly accelerated in the presence of cyclic loading. Of particular interest was the occurrence of an anomalous region of persistent debonding that developed below ∼10 −8 m s −1 under both monotonic and cyclic loading. In this region, debond-growth rates were characterized by a weak dependence on the applied loads, a strong dependence on moisture activity, and the absence of a measurable threshold below which debonding could not be measured. We propose a new stress-dependent transport model that describes the moisture diffusion mechanism responsible for this anomalous behavior.

The stress field in a [0°/90°] laminated composite plate containing a finite line crack

This paper deals with the construction of an asymptotic solution for the stress field in a laminated composite plate, with (0/90) stacking sequence. The plate contains through the thickness a line crack of length 2c and its perimeter boundaries are sufficiently far away from the crack so that no edge effects are present. The stress field is derived explicitly, and includes a correction factor to account for the laminate effects in the third dimension. The stress σzz is a maximum at an angle of θ ≈ 83 ◦ (see Figure 3). The stress field may now be used to bridge the gap between macro and micro mechanics and to derive a series of fracture criteria, at the micro and macro level, which ultimately will provide us with a better understanding of the formation of the damaged zone ahead of the crack tip. For example, the stress field is used to derive one such approximate fracture criterion for mode I loading and for a self similar type of fracture, similar to that of Griffith. This criterion shows how the periodic length of the material lay-up microstructure effects the fracturing characteristics of the material system. Comparison with some experimental observations for two different material systems shows a fairly good agreement which substantiates the predicted influence. Despite careful design, practically every structure contains stress risers due to the presence of inclusions, holes or cracks. Bolt holes and rivet holes are necessary components for structural joints. It is not surprising, therefore, that the majority of service cracks nucleate in the vicinity of a stress riser. While the subject of stress risers is certainly familiar to engineers, the situation is significantly more complex in the case of high-performance laminated composite materials. The presence of a hole or a crack in the laminate introduces significant stress contributions in the third dimension which create a very complicated three-dimensional (3-D) stress state in the vicinity of such discontinuities. Moreover, this complex state of stress may depend on the stacking sequence of the laminate, the fiber orientation of each lamina as well as the material properties of the fiber and of the matrix. Ultimately, these stress risers form a primary source of damage initiation and property degradation, particularly in the presence of cyclic loading. Experimental investigations carried out by Bakis and Stinchcomb (1986) on graphite- epoxy laminates which have been weakened by a circular hole give us a better insight of this damage growth development under the action of cyclic loading. In general, the progression of this damaged process may be characterized as (i) debonding along fiber-matrix interfaces, (ii) matrix cracking parallel to the fibers, (iii) matrix cracking between fibers, (iv) delamination along the interface of two adjacent laminae with different fiber orientations, and (v) fiber breakage.

Fracture resistance of materials with translational hardening in the presence of cyclic loading

We use the examples of two types of titanium alloys that are currently widely used to study the effect of translational hardening on the fracture resistance of materials subject to cyclic loading. We examine regularities in elastoplastic deformation, the stability of hardening over time, and critical values of crack length and fracture stress.