Papers by Keyword: Three-Point Bending

Abstract: Rolled 7xxx-series Al alloys exhibit pronounced microstructural anisotropy (pancake grains and particle stringers) that can strongly affect fatigue initiation and-crack growth. In the current study, an AA7075-T6 plate was examined in three orthogonal machining orientations—L–S (longitudinal), L–T (long-transverse) and T–S (short-transverse)—using high-cycle three-point bending fatigue at room temperature (R = 0, f = 25 Hz, σ_max = 360–400 MPa, i.e., ~0.79–0.88σ_y). Optical/SEM observations reveal elongated grains and a grain-density gradient through thickness, accompanied by orientation-dependent distributions of intermetallic particles. Despite only small differences in monotonic response, fatigue performance is strongly orientation-dependent: the T–S specimens exhibit the longest lives in the S–N curves. Fractography and striation-based kinetics show the lowest Paris-regime crack-growth rate for T–S (da/dN ≈ 1.85×10⁻⁷ m/cycle at ΔK ≈ 10.5 MPa√m), while L–S shows the fastest growth (da/dN ≈ 4.3×10⁻⁷ m/cycle at ΔK ≈ 13.0 MPa√m). The improved T–S fatigue resistance is discussed in terms of crack-path interaction with grain boundaries and particle populations (coherent/penetrable vs non-coherent/coarse particles), which can either deflect/retard cracks or act as initiation sites. The results provide a compact microstructure–mechanics map for rolling-induced anisotropy in AA7075-T6 under bending fatigue.

Abstract: Carrier-based aircraft takeoff and landing devices endure repeated high-speed, high-energy, and high-load impacts during operation. This repeated impact results in fatigue damage, a primary cause of failure in these devices, commonly known as impact fatigue. To address multiple impact fatigue failures in the takeoff and landing process of carrier-based aircraft, an investigation into the three-point bending impact fatigue characteristics of ultra-high-strength steel 23Co14Ni12Cr3MoE (abbreviated as A100 material) was conducted using experimental and microscopic techniques. A reproducible impact loading device for three-point bending tests was devised, leveraging a drop hammer impact tester. This innovative setup enabled the proposal of a three-point bending impact fatigue testing method. Test specimens featuring U-shaped, V-90°, and V-60° notches were designed, drawing inspiration from the Charpy pendulum impact test for metallic materials (GB/T 229-2007). Impact fatigue testing was then performed on the drop hammer tester across five distinct energy levels: 25J, 30J, 35J, 40J, and 45J.The study comprehensively examined the load response, energy absorption, and fatigue life of the A100 material in relation to the number of notches and impacts. Post-experiment analysis using a light microscope and SEM electron microscope revealed key morphological features of the A100 material's impact fatigue fracture surface: the crack initiation zone, stable crack propagation zone, rapid crack propagation zone, and shear lip area. Notably, as impact energy rose, the crack propagation zone expanded, while the shear lip area contracted.These findings contribute significantly to understanding the fatigue behavior of A100 material under repeated impact conditions, critical for enhancing the durability and safety of carrier-based aircraft takeoff and landing devices.

Abstract: Experimental work has been performed on the behaviour of glass/epoxy, aluminum, and aluminum-glass/epoxy empty and polyurethane foam filled tubes subjected to three-point bending. Tubes were of circular and square cross section area. Hand layup method was used to fabricate the tubes. Each tube is made of six layers. Inner diameter and total length of the tubes were 50 mm and 250 mm respectively. Bending load-displacement response, crush force efficiency, and absorbed energy were drawn and discussed. Effect of foam filler, material of the tube and stacking sequence on the maximum bending load was investigated. Energy absorption was determined and discussed. failure mode was investigated. It has been found that the polyurethane foam filler increased the maximum bending load and the energy absorption of the circular and square cross section area tubes. Using hybrid aluminum-glass/ epoxy enhanced the bending load and absorbed energy of the aluminum tubes. Cracks were observed at the upper and lower surfaces at the centre of the glass/epoxy tubes. While the aluminum tubes deformed significantly with either no cracking or with one crack appeared at the centre of the top surface of the tube.

Abstract: Three dimensional finite element models of composite joints were established to investigate the load-displacement behavior, failure mode of multi-axial tubular joints under bending load, and stress-strain relationship in some key positions. The joints were prepared by plain weave fabric. The effective elastic constants of fabric composite were calculated using meso-mechanics theory. A progressive failure analysis was performed using ABAQUS software to obtain the ultimate strength and failure mode of the sample. In addition, the damage process, failure mode and damage position was further studied. The bending properties of the joints were also presented by quasi-static load test using a three-point bending test device. Results of the ultimate load and damage analyses are compared to experimental data. The accuracy of the method was proved by the consistency of the relation between the load displacement curve trend and the correlation of the damage position and failure pattern.

Abstract: The bimodal, equiaxed and Widmanstatten microstructures of TC4 titanium alloy were obtained through different heat treatment processes. The content of primary α phase in the bimodal and equiaxed microstructures was measured to be about 40% and 90%, and the average size was about 9.4μm and 7.9 μm. Three types of microstructure fatigue S-N curves are obtained, which are successively descending type, single-platform descending type and infinite life type. The order of very high cycle fatigue performance is Widmanstatten>equiaxed>bimodal, but the anti-fretting fatigue performance of Widmanstatten is the worst. The grain refinement makes the fatigue performance of the equiaxed better than that of the bimodal. The second process is determined as the best heat treatment method. There is no significant difference in the life of the crack propagation stage. The very high cycle fatigue life mainly depends on the crack initiation stage. In the bimodal and the equiaxed, the crack initiates in the primary α phase of the subsurface, and the crack in the Widmanstatten initiates in the coarse α 'grain boundary of the subsurface.

Abstract: In order to determine the evolution features of deformation twins for TA2 commercial pure titanium (cp-TA2), the TA2 samples were bent under different bending angles in three-point bending tests via a universal testing machine. The electron backscatter diffraction (EBSD) technique was applied to identify the grain boundaries (GBs) and twin boundaries (TBs) in the bending areas. The results reveal that the type of deformation area would effect the evolution of different deformation twins. It is inferred that the state of stress would promote the multiplication of the same type of deformation twins.

Abstract: Surface treatment on metal can alter physical and mechanical properties. Understanding the physical and mechanical properties of the archwires is essential for the management of orthodontic treatment. Methods: This study used digital micrometer, universal testing machine, and surface hardness tester for measuring dimension, unloading force, and surface hardness of two different type of nickel-titanium (Ni-Ti) archwires: commercially available Ni-Ti (NT-N) and surface treated Ni-Ti by fine particle shot peening (FPSP) method (NT-F). Statistical analysis was undertaken using a paired T-test (α=0.05). Results: No significant difference was found on both vertical and horizontal dimensions of NT-N and NT-F (p= 1.00 and 0.796 respectively). For bending and surface hardness test, significance difference was found (p<0.001 and p<0.001 respectively). Conclusions: The NT-F archwire provided lower unloading force and surface hardness but there was no change in size when compared with NT-N.

Abstract: Fracture behaviors in concrete beam subjected to three-point bending was numerically simulated using extended finite element method (XFEM). The entire load-displacement curves and crack path obtained by numerical simulation were compared with that measured from experimental tests. Compared with the experimental results, the errors of numerical P_c and δ_c were smaller than 10% and the error of CMOD_c was lower than 2%, verifying the validity and accuracy of XFEM model. Whether a XFEM simulation or a test, the propagation direction of the main crack is toward to the upper loading point. At the peak load, the crack lengths measured by ESPI and XFEM were 93 μm and 97 μm respectively.

Abstract: Fracture behaviour of a crack approaching a bi-material interface is investigated. A three-point bending configuration of a cracked specimen is simulated numerically by means of the finite element method and the interaction between the crack and aggregate is studied. The crack deflection angle is estimated by means of the maximum tangential stress criterion in its classical as well as generalized (multi-parameter) form considering the Williams’ power series with various numbers of the higher-order terms for the tangential stress approximation. The influence of the elastic mismatch and of other parameters on the calculated initial crack propagation angle is discussed.

Abstract: Extruded polystyrene (XPS) is a material with applications in the building industry, where it is typically used as thermal insulation. Fracture experiments in the three-point bending configuration were conducted on XPS beam specimens with an initial stress concentrator made before testing. The nominal dimensions of the beams were 40 × 40 × 160 mm. The depth of the initial edge notch on the bottom side of the specimen was approximately 1/3 of specimen height. The span length was 120 mm. Load vs. displacement diagrams were recorded during fracture tests, and subsequently the modulus of elasticity (E), effective fracture toughness (K_Ice) and specific fracture energy (G_F) of the XPS were determined. The mean values obtained for the mechanical fracture parameters and coefficients of variation (number of specimens) were the following: E = 10.7 MPa, 9.2 % (7); K_Ice = 0.0547 MPa∙m^1/2, 16.7 % (3); G_F = 183.2 J∙m^–2, 34.3 % (3).