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Blade shape affects the cutting resistance of the blade, and it can be designed to reduce the cutting resistance. In this study, two types of blades (I-type blade and L-type blade) with an identical rectangle profile projection (width 300 mm, height 500 mm) were compared by experiment of soil cutting. The cutting rake angle of the blades is fixed at 90° to ignore the vertical cutting resistance, and then, we can only focus on the horizontal cutting resistance which can be regarded as the drought force. Thirty groups of soil cutting test were carried out in a soil bin filled with sandy soil in which the moisture content was neglected, and cutting depths considered were 30, 60, 90, 120 and 150 mm. The effects of the cutting depth and the horizontal plate length on the cutting resistance of the blades were studied. The results showed that the cutting resistance increases with the increase in the cutting depth, which present a curvilinear relationship for each blade. When the cutting depth is the same, cutting resistance decreases firstly then rises with the increase in the horizontal plate length. Therefore, it can be believed that the L-type blade must have an optimum shape for soil cutting. In 25 group comparisons between five L-type blades and the I-type, the L-type blades presented lower cutting resistance in 23 group tests. However, the optimal shape in the present study is that the L-type blade length is about 45 mm for different cutting depths, which can make guidance for us to design the shape of the blade.

In order to improve the performance of the sparrow search algorithm (SSA), in this paper, a novel series of SSA variants is proposed by combining SSA with improved Tent chaos mutation (IT), Lévy flights mutation (LF), elite opposition-based learning mutation (EOBL), variable radius mutation (VR) and the combination of IT, LF, EOBL, and VR, namely, ITSSA, LFSSA, EOBLSSA, VRSSA, and CMSSA, respectively. Initially, the performance of these variants is evaluated on a comprehensive set of 31 benchmark test functions. Moreover, the performance of the best algorithm among these variants is compared with 19 state-of-the-art optimization algorithms to validate its performance on 31 benchmark test functions. The convergence and computational complexity of the best variant are also analyzed to test exploration, exploitation, and local optima avoidance. It is then employed on eight real-world constrained engineering problems to further verify its robustness. The experimental results reveal that the best algorithm of SSA variants outperforms other competitors and is highly effective in solving real-life cases.

Working resistance of blades is influenced remarkably by cutting rake angle during soil cutting and bulldozing process. In order to further reduce the effect of the working resistance on soil cutting and bulldozing, the blades with horizontal plates in three different lengths were developed. Self-designed experiment system was used to carry out soil cutting and bulldozing. Twelve groups of soil cutting and bulldozing tests were completed with four different cutting rake angles under cutting depth of 90mm in grading soil. The results show that the blades with horizontal plates can reduce the working resistance when the cutting rake angle is greater than a certain valve. There is more significant effect on the working resistance when the soil cutting and bulldozing are under larger cutting rake angles, and it would be have adverse influence when the cutting rake angle is less than 45 degree. In addition, the length of the horizontal plate has an optimal value to minimize the working resistance under different cutting rake angles. Therefore, it is a feasible way to reduce the working resistance by designing the blades with horizontal plates for earthmoving machine under certain conditions.

To investigate the cracking reason in welding structure with transition changing faces at cylinder block on boom of medium excavator during fatigue test, the finite element model of boom was established by using ANSYS finite element software. The stress distribution of the boom was obtained under fatigue loading spectrum of medium excavator. In addition, the fine model of welding structure with solid element length 2 mm was set up with the help of sub-model technology in ANSYS software to get the accurate hot spot stresses around welding toes. Finally, the fatigue life of this welding structure was calculated according to IIW fatigue class. The results show that the stress gradient along with the thickness direction can be acquired by fine three-dimensional finite element sub-model of welding structure. Therefore, the weakest point in thick plate was located, which was in accordance with the experiment result.

Fracture of brittle ceramics initiated from shallow surface cracks comparable to their average grain sizes (G) can fluctuate significantly. Such fluctuations can contain crucial information on the inherent relations between the average grain size G and bulk ceramic properties such as the tensile strength ft and fracture toughness KIC. It was proposed in this study that the characteristic crack a*ch = 0.25(KIC/ft)2 = constant × G, inspired by observations of strength distributions with different a*ch/G ratios. It was found that normal distributions with the smallest standard deviation exist around a*ch = (2.5–3.5) × G, based on quasi-brittle fracture results of four different ceramics with G from 2 to 20 μm and shallow surface cracks from 100 nm to 650 μm. Using the average value of the relative characteristic crack a*ch/G ≈ 3, the mean and standard deviation (σ) were determined by normal distributions for both the tensile strength ft and fracture toughness KIC. Quasi-brittle fracture of those fine-grained ceramics based on the mean values and standard deviations was thus predicted. The upper and lower bounds with 96% reliability (±2σ) specified by the normal distributions covered nearly all experimental data ranging from the strength-controlled to toughness-controlled asymptotic limits, and quasi-brittle fracture between the two. With the knowledge of the average grain size G, the tensile strength ft becomes the sole parameter required to describe the entire fracture range.

We studied the dynamic mechanical behaviour of three-dimensional (3D) random fibrous (RF) materials at various strain rates using a high-temperature split Hopkinson pressure bar (SHPB) system from 288 to 1423 K. The failure mode of 3D RF materials in the in-plane (IP) direction exhibits a shear fracture mode with an angle of ~30° at a strain rate of 300/s, and the bonding between fibres remains intact at 288 K despite the fracture in fibres. The variation of dynamic strength at a strain rate of 500/s (from 288 to 773 K, the strength increases from 4.72 ± 0.61 to 5.27 ± 1.03 MPa; from 773 to 1423 K, the strength decreases from 5.27 ± 1.03 to 3.36 ± 0.93 MPa) aligned well with observations of the static experiment with increasing temperature. We determined the strain rate sensitivity factor by fitting strength versus strain rate at various temperatures and observed a significant effect of the strain rate sensitivity on strength at 288, 773, and 1273 K. However, the effect of strain rate on the strength is low at the transition temperature of viscous flow and brittle deformation of 3D RF materials. These results can be used as the theoretical basis for the preparation and performance evaluation of 3D RF materials.

In this work, weld-repaired Bisplate80 joints without or with a buffer layer (BL) were subjected to a post-weld heat treatment (PWHT) at 930 °C for 1 h followed by air cooling. The mechanical properties and fracture mechanism of the PWHT specimens were compared to those from corresponding as-welded specimens to study the influence of the PWHT and to compare them with as-received Bisplate80 specimens to inspect the welding quality of the joints. Fatigue crack growth curves and micro-hardness profiles across the welded joints for the as-weld or PWHT conditions were measured together with relevant scanning electron microscope observations along the crack growth path. Special attention was paid to the areas at and around the welded interfaces. The results showed that the incorporation of a BL with an appropriate thickness significantly improved the fatigue crack growth behavior of the welded joint for the PWHT condition, as the da/dN over the entire area of the welded joint was much lower than for both the as-welded and as-received Bisplate80 specimens, showing that the incorporated BL greatly improved the fracture mechanisms of the fatigue specimens.

A simple method of applying and distributing multi-walled carbon nanotubes (MWCNTs) onto grit-blasted steel substrates has been investigated in this study to overcome the difficulty of mixing MWCNT...

By means of finite element modeling (FEM) and fatigue experiments, we study the fatigue performance of the rounded welding region between the diaphragm plate and closed rib of orthotropic steel bridge deck in this work. A local sub-model of the rounded welding region from the orthotropic steel bridge deck was developed to analyze the stress distributions. Based on the analysis results we designed the fatigue specimen for the fatigue test of this detailed structure. The fatigue experimental results revealed that the crack initiates from the weld toe of the rounded welding region and the stress concentration at the rounded welding region is the main mechanism of fatigue crack initiation. In addition, we propose three improvements to reduce the stress concentration of the rounded welding region, and the local structure optimization scheme of the diaphragm&ndash, rib weld can effectively improve the fatigue resistance of the detailed weld structure.

A closed-form fracture model with the consideration of the average aggregate size and crack-tip damage zone is used to analyse flexural strength of asphalt concrete using notched beams. Quasi-stable micro-crack formation and quasi-brittle fracture of these small samples with highly heterogeneous aggregate structures are formulated. While the apparent strength and fracture toughness of asphalt concrete based on Continuum Mechanics are size dependent, constant asymptotic “structural” tensile strength ft and “structural” fracture toughness KIC have been determined by this composite model from experimental results of notched beam specimens of any size with any notch length. Temperature (T) dependent ft and KIC measurements of asphalt concrete from −10 to + 23 °C, relevant to the real temperature environments, are then determined. The characteristic microstructure Cch in the model is the average aggregate size. The maximum failure load Pmax of asphalt concrete under three-point-bending (3-p-b) is linked directly to its constant “structural” tensile strength ft for a given temperature environment, independent of sample size and notch/crack length. In addition, although KIC is not valid for asphalt pavement with limited thickness, its influence is reflected through the “structural strength” criterion based on ft and Cch. This simple model can also be used as a design tool for asphalt concrete property optimization.

This study reveals the micro-structural details on the metal substrate surface prepared by grit blasting, and then proposes a simple resin pre-coating method aiming at full wetting of the substrate surface for stronger adhesive bonding. The resin pre-coating solution consisting of around 90% acetone and around 10% resin without hardener is used as a primer, which can be sprayed or blushed onto the grit-blasted metal substrate. The acetone solution can carry resin deep into micro-cavities created by grit blasting and effectively coat and wet micro-debris so that micro-voids or gaps between the adhesive joint and metal substrate can be removed. Since the resin pre-coating does not contain hardener and remains wet, the wettability of the substrate is also improved. The normal epoxy adhesive with hardener can then be applied onto the substrate surface. Despite having the primer-like function, the proposed resin pre-coating method still maintains the simplicity of one epoxy resin system. Based on the current study, a resin and acetone solution without hardener does not seem to have adverse effects on the final bonding strengths of adhesive joints, although acetone is known to have detrimental effects on resin and hardener adhesive systems. Four different surface conditions are examined, each having 14 specimens: (1) Grit-Blasted (GB) surface, (2) GB-surface with ultrasonic cleaning, (3) GB-surface with resin Pre-Coating (PC) only, and (4) GB-surface with both ultrasonic cleaning and PC. 25% improvement in the shear strength has been achieved by the resin pre-coating method, even without ultrasonic cleaning, in comparison with 8% improvement after ultrasonic cleaning. These results show GB-surface with PC is beneficial to adhesive bonding, which can be adopted for structural applications even if thorough substrate surface cleaning on site is not possible. The improved wettability of metal substrates after resin pre-coating contributes to the maximum possible utilization of the contact areas over the roughened substrate surfaces and thus leads to the enhanced adhesive bond strength.

The wettability of grit blasted steel substrates is improved by a simple surface treatment method proposed in this study. The shear strength of epoxy adhesive joints has been improved by over 50% after optimizing this “resin pre-coating” surface treatment method. The shear strength is further enhanced by incorporating multi-walled carbon nanotubes (MWCNTs) and short Kevlar fibres into the adhesive joints, with over 70% improvement for the combined surface-treated and MWCNTs toughened adhesive joints. The reinforcing mechanisms along the “interfacial zone” defined by the surface topography and the toughening mechanisms within the “composite adhesive joints” because of MWCNTs and short Kevlar fibres are discussed together with detailed Scanning Electron Microscopy (SEM) observations and experimental results.

In this study, a new bench device with full-scale fatigue test for excavator stick was designed. The test bench has the function of dynamic load self-balancing, because a part of the load applied to the specimen of stick is directly transferred to the pillars of the test machine through the high-strength bolts connection. Accordingly, the ground under the test machine was not affected by the test load. However, some bolts located on the fatigue test bench failed and fractured during fatigue testing for excavator stick. To determine the failure reasons of bolts, mechanical and scanning electron microscope (SEM) analyses were conducted. The tensile stress of bolt group under ultimate load was evaluated via finite element model (FEM) of test bench according to test load spectrum. Moreover, under the test load spectrum, the stress range of bolt group was obtained and the fatigue life prediction of bolts was conducted by referring to Eurocode 3. It should be noted that the results of numerical simulation of fatigue lives for failure bolts were consistent with the actual lives of failure bolts during test. A fractured surface on one of the failed bolts was examined by SEM observation to determine the failure initiation and failure mode.

In this study, we perform three-point-bending tests for 3-dimensional random fibrous (3D RF) material specimens of two porosities (87% and 83%) with a crack. The crack with two different crack-length-to-specimen-width ratios (0.2 and 0.5) is considered. Using the tensile strength obtained from experiments and a characteristic average fiber spacing parameter from an equivalent orthotropic fiber network model, a simple theoretical model is developed to evaluate the fracture toughness of 3D RF material. This model gives the fracture toughness of 3D RF material, which is in good agreement with that from compact tension test, and better than the results calculated via the American Society for Testing Materials (ASTM) standard for three-point-bending test. This fact not only rationalizes the use of average fiber spacing size in the developed model, but also demonstrates the model efficiency in evaluating the fracture toughness of 3D RF material. Further, considering the temperature effect on the fracture strength of material, this theoretical model can be successfully used to predict fracture toughness of 3D RF materials at elevated temperatures (299 K~1073 K).

The working load of excavator is complex and the working environment is bad. As the main part of excavator, the boom bears a large complex load and is prone to fatigue damage. A large hydraulic excavating boom is taken as the research object in this paper, aiming at the damaged position in the platform fatigue test, that is, the web butt weld on the root of the boom, and the fatigue life of this part is evaluated by means of hot spot stress and load spectrum. The result shows that the theoretical lifetime of this part is 4148 h, which is completely agree with the equivalent life 4278 h when the cracks appeared in bench fatigue tests. Accordingly, the hot spot stress approach is suitable for the fatigue life evaluation of the boom, and its accuracy is high.

To evaluate the fatigue reliability of the excavator working device, the fatigue tests of 2 sets of moving arm and bucket rod of medium-sized excavators with self-weight of 26000 kg were carried out. The virtual augmented sample method (VASM) combined with Bootstrap method was used to analyze the reliability of the excavator working device under extremesmallsamples, and the interval and point estimations of life parameters were obtained. Based on the lognormal distribution of the excavator working device, the reliability evaluation model of the excavator working device was esTablelished, and reliability indexes, such as reliability function, failure distribution function, inefficiency function, reliable life and so on, were obtained. And the results of fatigue safety life under different confidence and reliability were calculated. The evaluation results show that the average failure time of the excavator working device is 5885 hours under the confidence of 75%, which provides an important reference for the design, the safety inspection and maintenance decision of the excavator working device.

Large-scale brick-mortar structures and tough/strong nacre have common layered structure features. If enlarged by 20,000 times, fracture patterns in natural nacre consisting of micro-layered structures around 2 μm in thickness are virtually identical to those in large-scale brick walls. In this study, large brick-wall blocks about 3 m long and over 1 m tall were tested under three-point-bending and explained by a simple closed-form model. Two notch lengths (two and four brick heights) and two wall heights (about 1.1 and 0.6 m) were tested with 35 brick-mortar blocks. A linear relation between the maximum fracture load Pmax and the equivalent area Ae was established with the “structureal” tensile strength ft of brick walls as its slope, affirming one of the most common physical relations in Solid Mechanics, Pmax = ft × Ae. The equivalent area Ae contains all brick wall dimensions including the brick height Cch. As the characteristic structural measurement of brick wall elements, Cch plays a key role in modelling of the overall damage zone in front of the initial notch.

Indented patterns, about 40 μm wide and 30 μm deep, were created by pressing down a hardened steel file onto the surface of steel substrates using Instron test machine. We examined the penetration of epoxy into those micro-indented patterns and their interactions with Kevlar fibres (diameter of around 12 μm), and their influences on the shear strength of epoxy adhesive joints. To ensure complete wetting of the patterned substrate surface, resin pre-coating was applied first. Three different acetone/resin (without hardener) solutions were prepared for this purpose: they contained 1 wt%, 3 wt% and 5 wt% of resin in acetone, respectively. For the purpose of comparison, plain steel substrates polished by #120 sandpaper were also prepared. It had been found that the patterned substrate coated by the 3 wt% resin/acetone solution yielded the highest shear strength, showing about 20% improvement in comparison with that of polished steel substrates. Only limited Kevlar fibres were found within the indented...

The cutout hole locating at the place of rib-to-diaphragm welded connection is adopted to minimize the restraint, which is caused by the floor-beam web to rib rotation at the support due to the unsymmetrical loads in orthotropic deck. In practice, an inevitable problem is that there is a large number of welding joint's cracks formed at the edge of cutout hole. In this study, a comparative experiment is carried out with two types of cutout hole, the circular arc transition and the vertical transition. The fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by finite element analyses. The results are compared with the ones of the fatigue tests which are carried out on these full-scale specimens. Factors affecting the stress range are also studied.

a b s t r a c t Welding residual stresses, Vickers hardness and microstructure of welded high-strength low-allow steel, known for high strength and low carbon content, were studied under the following conditions: as- received high-strength low-alloy steel, welded high-strength low-alloy steel without a buffering layer, and welded high-strength low-allow steel with various thickness buffering layer. A soft buffering layer with a modest thickness between the parent metal and the weld metal could be incorporated to welded high-strength low-alloy steel to effectively reduce the widths of tensile residual stress zone and welding softening zone, to change the residual stress (in y-direction) nature at the weld root from tensile to com- pressive, and to refine the grains of the welded high-strength low-alloy steel. The width of the tensile residual stress (in x-direction) zone was approximately equivalently to that of the welding softening zone for those welded high-strength low-alloy steel with and without buffering layers. © 2013 Elsevier B.V. All rights reserved.

The effects of tensile over-load (OL) on fatigue crack growth behavior of a weld-repaired high-strength low-alloy (HSLA) steel were studied by measuring both the fatigue crack growth rate and sample-thickness variation along the fatigue crack growth path. The thickness variation, indicating the degree of plastic deformation (PD), provided an indirect measurement of associated residual compressive stresses at the crack-tip. The applied tensile OL with one-hour holding period in each test generated a damage zone at the crack tip. Microscopic details of the crack-tip damage zone were characterized by scanning electron microscopy. Three groups of expanded compact-tension (E-CT) samples, 10 mm in thickness, were tested: weld-repaired HSLA without soft buffer layer (BL), and weld-repaired HSLA with 4 mm or 10 mm thick BL. The experimental results showed that the OL-induced PD, closely linked to the crack-tip residual compressive stresses, reduced the subsequent fatigue crack growth rate, and that the HSLA with a 10 mm BL had the lowest growth rate, indicating a soft BL with an adequate thickness could further improve the fatigue resistance.

Binhua Wang, Pengmin Lu, Yuhong Shao Key Laboratory for Highway Construction Technology and Equipment of Ministry of Education, Chang’an University, Xi’an 710064, Shaanxi, China Email: wangbh@chd.edu.cn Abstract In order to minimize the restraint provided by the floor-beam web to rib rotation at support due to unsymmetrical loading in orthotropic decks, the structure of cutout holes are adopted at the place of rib-to-diaphragm welded connection. However, there is a large number of welding joint’s cracks formed at the edge of cutout holes. In this study, the comparative specimens with two types of cutout holes are designed, i.e. the circular arc transition structure and the vertical transition structure. And the fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by use of finite element analyses. The results of the finite element calculations are compared with the results of the fatigue tests which are carried out on these full-scale specimens.

Residual stresses (RS) in a bulk weld-repaired steel structure and thin samples sliced from the welded-section are different due to inevitable variations in the stiffness and boundary conditions. In this study, thin extended compact tension (E-CT) samples for fatigue crack growth measurements were sliced from three extensively weld-repaired high-strength low-alloy (HSLA) blocks with three different welding conditions, i.e. welding with a 4 or 10 mm thick soft buffer layer (BL) and welding without the soft BL. Deformation in the thin E-CT samples with notches due to the partial release of welding-induced RS) was measured, and then the samples were used to measure the fatigue crack growth. In this study, we reported detailed measurements of residual stress-induced (RS-induced) deformation in thin test samples and corresponding fatigue crack growth behavior of an extensively weld-repaired HSLA with or without a thin BL. Three groups of E-CT samples were prepared: weld-repaired HSLA without BL, and weld-repaired HSLA with a 10 mm or 4 mm BL. The RS-induced deformation and corresponding fatigue crack growth were measured, and studied together with the influence of BL. The results showed that the incorporation of a 4 mm BL had a profound influence on reduction of the RS-induced deformation, and the incorporation of a 10 mm BL had a significant influence on the fatigue crack growth behavior in the parent metal, heat-affected-zone and weld metal. Detailed SEM observations show that fatigue characteristics of the weld-repaired HSLA were also influenced by the buffer layer and welding-induced RS.

It is a contradiction to homogeneous material fatigue behavior characterized by widely used linear Paris law, welded-joint fatigue issues need to be reassessed because fatigue crack growth behavior going through heterogeneous region will be different. For a welded joint, log(da/dN) is no longer linearly related to log(ΔK) in heterogeneous region because of the change in fatigue properties resulting from the welding process. Theoretical model of the fatigue crack growth rate without artificial adjustable parameters was proposed by considering the effects of heterogeneity in a welded joint and load-amplitude variation on fatigue crack growth curve. In this fatigue heterogeneous region, the relationship between log(da/dN) and log(ΔK) is similar to a concave-down parabola. Predicted results from the proposed model agreed better with the experimental data obtained from fatigue tests conducted in this study and open published literatures for welded joints in comparison to the widely used Paris model.

A soft buffer layer (BL) between the weld metal (WM) and the parent metal (PM) was introduced in this study. To study the effect of a BL on mechanical properties, two types of joints made from welded high-strength low-alloy (HSLA) specimens with or without a BL were prepared. To investigate the influence of the notch location, the welded HSLA specimens machined with a U-notch in the WM or the PM. These conditions were examined to determine the effects of the BL and the notch location on the fatigue characterizations and the microscopic features of the fatigue-fractured surface. Extended-compact tension (E-CT) specimens were used for all tests. Paris fatigue curves and hardness distributions of the welded HSLA specimens with or without a BL were measured, and relevant scanning electron microscope (SEM) images were taken. The results showed that the presence of a BL significantly improved the fatigue crack growth behavior when a U-notch was in the WM. The notch location greatly influenced the fatigue behavior and the surface features of the fatigue-fractured specimens.

The microstructure variation and its subsequent influence on the fatigue behavior and Vickers hardness of an extensively weld-repaired high strength low alloy (HSLA) were investigated in this study. Microstructures of the as-received HSLA, or parent metal (PM), welded HSLA without buffer layer (BL), and welded HSLA with 4 or 10 mm BL between the PM and weld metal (WM) were examined and compared with the corresponding fatigue behavior, hardness measurement, and fatigue-fractured surface. It was found that the fatigue resistance and hardness in part of the WM and in the melted parent metal (MPM) during welding of the welded HSLA without BL were lower than those of PM. However, the welded HSLA with a 4-mm-BL produced a marked increase in fatigue resistance and hardness, especially within the WM, within the mixed area of BL and MPM (BL + MPM). This was because the WM and MPM of welded HSLA without BL had block ferrite and coarse columnar grain structures. Furthermore, no obvious differences were found in fatigue property, hardness and microstructure between the MPM of welded HSLA without BL and the BL + MPM of welded HSLA with 10-mm-BL. In addition, optical microscopy and SEM examinations of the corresponding regions revealed that block ferrite and non-metallic particles were the main reason of poor fatigue resistance and low hardness.

To understand the effect of microstructure on mechanical properties of weld-repaired high strength low alloy (HSLA), as-received and weld-repaired HSLA with and without buffer layers (BLs) were prepared. Microstructure analysis was carried out using optical microscope and SEM, and mechanical properties were measured by Vickers hardness test and fatigue test. The fatigue resistance of weld-repaired HSLA without BL was deteriorated with comparing to parent metal (PM). Meanwhile, Vickers hardness (VH) showed an obviously reduction in the melted parent metal (MPM), which was due to formation of predominately block ferrite. For the weld-repaired HSLA with BL, the VH and fatigue resistance increased with the incorporation of 4 mm BL, which was mainly due to formation of lath ferrite and fine-grained pearlite and bainite. When BL thickness increased to 10 mm, the VH and fatigue resistance decreased, which was because the thick BL diluted the MPM. VH number from low temperature (below melting point) heat affected zone (HAZ) fluctuated, but had a little scatter. However, the fatigue crack growth rate from HAZ was not obviously affected by the welding as comparison with the PM.

Heat-affected zones (HAZs) in extensively weld-repaired Bisplate80, or the parent metal (PM), have been studied and examined using hardness measurements in conjunction with fatigue crack growth measurements and detailed scanning electron microscopy (SEM) observations. Three different groups of specimens have been prepared, i.e. as-received PM, weld-repaired PM with a thin 4 mm BL between PM and weld metal (WM), and weld-repaired PM without BL. The extended compact tension (E-CT) specimens for fatigue measurements are prepared according to the ASTM specifications, which are also used for hardness measurements. Hardness and fatigue crack growth variations across the boundaries between WM, BL and PM have been measured together with detailed SEM observations. It has been found that the welding process without BL reduced both hardness and fatigue resistance, especially around the weld interface and within the HAZ. Incorporation of a thin soft BL between WM and PM has increased both hardness and fatigue resistance around the weld interface and within the HAZ.

Fatigue crack growth properties and Vickers micro-hardness of a weld-repaired high-strength low-alloy steel, known for high strength, low carbon, excellent notch toughness and good weldability and formability, have been studied under the following conditions: as-received high-strength low-alloy, weld-repaired high-strength low-alloy without buffer layer, and weld-repaired high-strength low-alloy with various thickness buffer layers. Those conditions are examined to determine the respective fatigue crack growth behaviors and Vickers hardness distribution, and the effects of different weld-repaired conditions on fatigue characterizations and microscopic features of the fracture and fatigue surface. The extended-compact tension specimen geometry is adopted in this study for all tests. Paris fatigue crack growth curves and the hardness distribution across weld metal, buffer layer and parent metal has been measured together with the relevant scanning electron microscope observations along the fatigue crack growth path, with special attention at and around the interfaces between the weld metal, buffer layer and parent metal. The results show the presence of the BL of a moderate thickness has a significant influence on the fatigue crack growth behavior in the heat-affected zone and around the interface between buffer layer and parent metal. The fatigue resistance of the selected high-strength low-alloy + buffer layer + weld metal tri-metal system is higher than that of the high-strength low-alloy + weld metal bi-metal system.

The study on dynamic response of pavement under real transportation load is one international thermal topic. In view of the characteristics of the construction process of asphalt pavement and the dynamic response under heavy truck, one strain sensor was built up which can detect the dynamic strain of pavement under moving load. And corresponding tests were carried on in laboratory and in field road. It's found that the sensor not only can bear the destruction of high temperature and shearing, but also can satisfy the test requirement on dynamic transfer. Without especially protection, the survival rate in field road arrived to 82%. It's also found that the influence of the rigidity of the base layers on the dynamic response is large, and found that the dynamic strain at the bottom of each surface layer under moving load presents not only tensile strain but also compressive strain.