Evaluation of Physical and Mechanical Properties of Cotton Warps Under a Cyclic Load of Stretch-Abrasion

The fatigue behavior of cotton warps was studied by a newly weaving load simulator (WLS) developed in our laboratory. Reborn hairiness, strength retention, and elongation retention of sized warps were adopted to evaluate the physical and mechanical properties of sized warps under stretch-abrasion cyclic loading. The influences of different fatigue cycles on the above three indicators were also discussed. The results indicated that the fatigue behavior of the cotton warps accompanied by abrasion yields a three-parameter Weibull distribution. All the fitting plots show acceptable linearity. Moreover, there is a strong relationship of quadratic polynomial between the tensile properties and the fatigue cycle of the sized warps according to the scatter fitting (R2 > 91.08%). Similarly, there is also a good relationship of quadratic polynomial between the reborn hairiness index and the fatigue cycle of the sized warps (R2 > 94.51%). Finally, regardless of the strength retention, elongation retention, and reborn hairiness, the physical and mechanical properties of the cotton warps still change with the continuous increase of the fatigue cycle after 40% of the fatigue cycle, but it is not significant. The research was helpful to estimate the capacity of the warps to sustain failure.

Effects of external hydrogen on hydrogen-assisted crack initiation in type 304 stainless steel

Purpose The purpose of this paper is to present a crack initiation mechanism of the external hydrogen effect on type 304 stainless steel, as well as on fatigue crack propagation in the presence of hydrogen gas. Design/methodology/approach The effects of external hydrogen on hydrogen-assisted crack initiation in type 304 stainless steel were discussed by performing fatigue crack growth rate and fatigue life tests in 5 MPa argon and hydrogen. Findings Hydrogen can reduce the incubation period of fatigue crack initiation of smooth fatigue specimens and greatly promote the fatigue crack growth rate during the subsequent fatigue cycle. During the fatigue cycle, hydrogen invades into matrix through the intrusion and extrusion and segregates at the boundaries of α′ martensite and austenite. As the fatigue cycle increased, hydrogen-induced cracks would initiate along the slip bands. The crack initiation progress would greatly accelerate in the presence of hydrogen. Originality/value To the best of the authors’ knowledge, this paper is an original work carried out by the authors on the hydrogen environment embrittlement of type 304 stainless steel. The effects of external hydrogen and argon were compared to provide understanding on the hydrogen-assisted crack initiation behaviors during cycle loading.

Mechanical Assessment of Fatigue Characteristics between Single- and Multi-Directional Cyclic Loading Modes on a Dental Implant System

Mechanical testing based on ISO 14801 standard is generally used to evaluate the performance of the dental implant system according to material and design changes. However, the test method is difficult to reflect on the clinical environment because the ISO 14801 standard does not take into account the various loads from different directions during chewing motion. In addition, the fracture pattern of the implant system can occur both in the horizontal and the vertical directions. Therefore, the purpose of this study was to compare fatigue characteristics and fracture patterns between single directional loading conditions based on the ISO 14801 standard and multi-directional loading condition. Firstly, the static test was performed on five specimens to derive the fatigue load, and the fatigue load was chosen as 40% of the maximum load measured in the static test. Subsequently, the fatigue test was performed considering the single axial/occlusal (AO), AO with facial/lingual (AOFL) and AO with mesial/distal (AOMD) directions, and five specimens were used for each fatigue loading modes. In order to analyze the fatigue characteristics, the fatigue cycle at the time of specimen fracture and displacement change of the specimen every 500 cycles were measured. Field emission scanning electron microscopy (FE-SEM) was used to analyze the fracture patterns and the fracture surface. Compared to the AO group, the fatigue cycle of the AOFL and AOMD groups showed lower about five times, while the displacement gradually increased with every 500 cycles. From FE-SEM results, there were no different surface morphology characteristics among three groups. However, the AOMD group showed a vertical slip band. Therefore, our results suggest that the multi-directional loading mode under the worst-case environment can reproduce the vertical fracture pattern in the clinical situation and may be essential to reflect on the dental implant design including connection types and surface treatments.

Low-Cycle Flexural Fatigue Behavior of Concrete Beam Reinforced with Hybrid FRP-Steel Rebar

Studies examined experimentally the flexural behavior of concrete beams reinforced with the hybrid FRP-steel rebar but very few among them evaluated their fatigue performance. In this study, the fatigue test has been performed, and an analytical model for simulating the flexural fatigue behavior of the concrete beam reinforced with the hybrid bar considering its postyielding behavior is developed. A formula relating the postyielding fatigue strain of the rebar to the number of the fatigue cycle is suggested and used in the proposed procedure. The method simulating the low-cycle behavior of the reinforced concrete beam is found to be satisfactory and can predict the number of cyclic loading to failure.

A study of the magnetic fatigue properties of a magnetorheological elastomer

In this study, the magnetic fatigue properties of a magnetorheological elastomer were evaluated with and without a magnetic field. To accomplish the process, a magnetic fatigue tester and magnetorheological elastomer samples were designed and fabricated. The mechanical properties of the magnetorheological elastomer were determined under various fatigue cycle numbers and fatigue frequencies with and without a magnetic field. The shear modulus of the magnetorheological elastomer was also measured before and after the test to evaluate its mechanical properties. The results show that the shear modulus of the magnetorheological elastomer was larger in the presence of a magnetic field and decreased as the number of fatigue cycles increased because the internal structure became loose. Scanning electron microscopy images showed that the internal structure of the magnetorheological elastomer was loose under repeated application of magnetic fields.

Influence of Compressive, Tensile and Fatigue Stresses on Asphalt and Concrete Cement Road Pavements in Nigeria - Using Linear Elastic Theory

The high brittle nature of pavement structures have been carefully examined based on compressive, tensile strain and the harsh effects of fatigue cycle with reference to the base layer thicknesses and elastic strains during and after construction were examined. Subjection of asphalt and concrete-cement pavements to traffic loading and tyre pressure also influences the vertical stress and strain values for the asphalt and concrete materials under the same axial loading conditions. Using various fundamental equations under linear elastic conditions for the analysis of Asphalt and Concrete Cement structure revealed that both materials do respond differently to compressive and tensile stresses under similar mechanical conditions. Effect of compressive stresses and strains on concrete pavement is larger compare to asphalt pavement due to large thickness sub-base layer of its pavement structure. Both pavement layer thicknesses are independent of fatigue cycle under harsh traffic loading. Thus, concrete pavement has shown better fatigue resistance and less tensile strain values than asphalt pavements due to high pavement layer thickness regardless of the load distribution.