Combining nano-reinforcements with heterogeneous grain structure is a promising strategy for overcoming the strength-ductility trade-off in titanium matrix composites (TMCs). In this study, we developed a unique heterostructure with alternating alloy and composite bands, containing equiaxed fine grains (FGs) embedded with nano-(TiB + La2O3) particles and lamellar coarse grains (CGs), using an innovative powder-assembly and thermal-deformation strategy. The hetero-structured (TiB + La2O3)/IMI834 composite achieved remarkable mechanical properties, exhibiting an ultimate tensile strength (UTS) of 1292 MPa and a fracture elongation of 9.8 % at room temperature, and a UTS of 860 MPa at 600 degrees C. The strength enhancement was attributed to the hetero-deformation induced (HDI) strengthening caused by geometrically necessary dislocations density gradients near the CGs/FGs interfaces and the obstruction of dislocation motion by nano-reinforcements. Meanwhile, multiple slip in CGs, arising from the interaction between basal/prismatic < a > slip and HDI stress-induced pyramidal < c + a > slip, together with the activation of extra < c + a > dislocations in FGs, effectively coordinated deformation and generated extra strain hardening. Additionally, CGs with high deformability deflected and shielded cracks, and absorbed more strain, enhancing crack resistance and maintaining good ductility. This work provides a feasible strategy for designing and fabricating novel hetero-structured TMC with superior strength-ductility synergy.

The spatter produced during SLM significantly impacts the interaction between the laser and the powder bed, with linear energy density and the gas environment being key factors. Utilizing high-speed imaging technology and a novel image processing method, we developed a new spatter feature extraction algorithm to analyze the number, area, angle, and speed of the spatter under different energy densities and protective gas directions. The results indicate that as the linear energy density increases from 0.15 J/mm to 0.3 J/mm, the number and intensity of the spatter initially decrease and then increase. Comparative analysis shows that droplet spatter is significantly reduced when applying protective gas opposite to the scanning direction (GD-L) compared to along the scanning direction (GD-W). This study establishes a quantitative relationship between linear energy density, gas direction, and droplet spatter behavior. The mechanism of droplet spatter is discussed and divided into three categories. Predicting the recoil pressure and horizontal distance of spatter. It provides a theoretical reference for the parameter design and control of linear energy density and gas direction in the SLM process.

In order to improve the support removal efficiency and surface quality of selective laser melting workpieces, three-dimensional electrochemical-fluid field coupled numerical simulations of support removal before and after application of the flow field by electrochemical polishing are carried out to study and analyze the effects of electrolyte flow rate and polishing time on the support removal time and material loss from the workpiece surface. Experiments were designed to verify the simulation results and orthogonal experiments were used to investigate the effects of voltage, polishing time and electrode distance on support removal, material loss on the workpiece surface, surface roughness and to analyse corrosion resistance and hardness before and after support removal. The simulation results show that the support removal time under the electrolyte cycle is only 10 min, and the efficiency is improved by 50 %. When the electrolyte flow rate is 7 L/min, the mean dissolved thickness on the workpiece surface is the lowest, which is about 206.7 mu m, and the average error between the validated experimental results and the simulation is 8.22%. In the orthogonal experiment, when the voltage is 8 V, the polishing time is 14 min and the electrode distance is 150 mm, the support is completely removed, and the average material loss on the surface of the workpiece is about 170 mu m. The surface roughness is reduced by 78.60%, the corrosion resistance is improved and the hardness is reduced. At the same time, the data analysis of orthogonal experimental results to obtain the electrochemical polishing parameters on the surface material loss and surface roughness trend, to provide theoretical support and regular reference for follow-up.

Titanium matrix composites（TMCs），as a new generation of lightweight and high-performance metals are considered to be one of the most promising structural materials in the fields of aerospace，automotive and other high-tech industries. Compared with conventional micron-reinforced TMCs，nano-reinforced TMCs（NRTMCs）exhibit more significant advantages such as the desirable strength and ductility synergies and thermal deformation capacity. However，the performance potential of NRTMCs has not been sufficiently developed due to the problems of dispersion and thermal stability of the nano-reinforcements. How to introduce nano-reinforcements and maintain their stability during thermal mechanical processing has been a serious challenge for NRTMCs. This paper reviews the research progress of the process features，fabrication methods，microstructure characteristics and mechanical properties，analyses and identifies a series of fundamental issues such as dispersion and heat stability of nano-reinforced material that constrain its development，and proposes the directions for future research. The development directions of future research focus on:（1）interface reaction control and thermal stability design；（2）batch production and low-cost preparation technology；（3）research on special thermal deformation and heat treatment process；（4）tissue configuration design and toughness mechanism and （5）other key mechanical properties research of nano-particulate reinforced TMCs.

The effects of different heat treatment processes on the anisotropy of TB6 titanium alloy fabricated by laser deposition manufacturing were investigated.The evolution of microstructure was analyzed by using optical microscope （OM）， scanning electron microscope （SEM）， and transmission electron microscope （TEM）. The variation trend and influence mechanism of anisotropy with heat treatment were investigated. The present research shows that the original β grains and the morphology of the primary α phase （αp phase） are greatly affected by the thermal gradient. The original β grains in the microstructure of TB6 titanium alloy fabricated by laser deposition manufacturing are elongated along the deposition direction and are ellipsoidal. In addition， the relative slender αp phase parallel to the deposition direction is found. These two factors jointly lead to the anisotropy of room temperature tensile property of the as-deposited samples. The tensile strength in the vertical deposition direction （X-direction ） is 7.3% higher， the yield strength is 5% higher， and the elongation is 32.4% lower than that in the deposition direction （Z-direction）. The low-temperature annealing treatment has little effect on microstructure， only the anisotropy of plasticity is decreased. After high-temperature annealing treatment， the difference in aspect ratio of αp phase is significantly reduced， leading to the anisotropy of the room temperature tensile property decreases. The strength are still higher in the X-direction ， and the elongation is higher in the Z-direction. The strengthening mechanism of the solution-aging treating sample is completely changed due to the precipitation of the secondary α phase （αs phase）. In addition， there is no obvious preferential growth of αs phase after heat treatment， so the anisotropy of the room temperature tensile property tends to be eliminated as the strength increases.

Pores are the major factor inducing fatigue failure in laser-directed energy deposition (L-DED) Ti-6Al-4V alloy, posing obstacle to the application of the alloy in primary load-carrying components. Hence, it is essential to formulate criteria to identify critical pores that induce failure, an important step in evaluating the fatigue performance and predicting the fatigue life of L-DED Ti-6Al-4V alloy. In this paper, computed tomography was performed on tangentially blending fillets specimens to examine the distribution characteristics of pore geometric parameters, and location in the gauge section of the specimens. Then, fatigue experiments and fracture analysis were conducted. The results show that the location relative to the surface, size, and shape of the pores are the primary factors affecting fatigue failure. A stress state sensitive parameter was formulated by using location factors, projected area along the load direction, circularity of pores, and peak stress to establish a criterion for recognizing critical pores, the number of which can be reduced to two. The critical pore criterion based on stress state sensitive parameter was compared with those obtained via the other methods, proving its good applicability and effectiveness on identifying critical pores.

It is common to use heat treatment process to control the microstructure of additive manufacturing parts and improve the mechanical properties. However, there are few reports about the control of microstructure properties of WAAM hybrid inter-layer hammering fabricated parts by heat treatment. In this study, the effect of annealing on microstructure and mechanical properties of inter-layer hammering hybrid wire arc additively manufactured aluminum alloy was studied. The ratio variation of fine grain (FG) and coarse grain (CG) regions, grain size and dislocations were analyzed, and the strength-plasticity mechanism was revealed. The results shown that with the increase of annealing temperature, the ratio of FG and CG region changed from 4:1-1:5, grain growth and recrystallization happened in FG and CG regions, respectively, dislocations mostly retained in FG region and released in CG region. With the introduction of annealing and the increase of annealing temperature, the strength of hybrid manufactured samples gradually weakened while the plasticity first improved and then reduced. The best tensile properties of ultimate tensile stress 366 MPa and elongation 29.2% were achieved at 180 degrees C annealing. Compared with as-deposited sample, the synergistic enhancement of strength and plasticity in annealed samples is owing to dislocation strengthening, grain refinement, and heterogeneous structural strengthening. Compared with hammered sample, the strength retained and significant improved in plasticity of annealed sample, owing to dislocation released, grain refinement and heterogeneous structural.

Objective Aluminum matrix composites (AMCs) are widely used in the aerospace industry, transportation, electronics, and other fields because of their high specific strength, low cost, good corrosion resistance, and easy recyclability, which puts higher demands on their comprehensive performance to meet the damage tolerance design criteria. However, AMCs prepared by traditional methods are costly and complex, and the formed materials are prone to the phenomenon of mutual exclusion of strength and fracture toughness. To further improve the strength and toughness of AMCs and overcome the inverse relationship between them, in addition to the selection of the reinforcement material for the matrix, the preparation method and design of the spatial structure also play a crucial role in the construction of high-strength and high-toughness AMCs. The additive manufacturing method differs from the traditional preparation method in that it stacks layers of material onto a substrate and can obtain a free form by precisely regulating the phase evolution as well as the distribution of components and structures. Thus, as it can customize the structure and synthesize a variety of materials, this process is more suitable for developing heterogeneous structures. At the same time, bionic structures provide a new way of thinking for realizing high-performance materials by mimicking the regulation of existing microstructures in nature. Methods By adding titanium alloy skeleton structures with different volume fractions and sizes to the aluminum matrix, strengthand toughness-adjustable bamboo fiber-like Al-Ti composite structures were prepared. The micro/macro interfacial organization of the composite structure was observed, the chemical composition and elemental distribution of each phase were analyzed, the coordinated deformation ability of the composite structure under compressive stress was studied, and the deformation and interfacial toughening mechanisms of the composite structure were elucidated. Results and Discussions It is found that a diffusion reaction occurs in the interface of the titanium-alloy reinforcement skeleton and aluminum alloy matrix, forming a dense metallurgical bond, and the precipitated phases at the interface are Ti-Al intermetallic compounds (Fig. 3). Compared with traditional aluminum-matrix composite materials, this composite structure has a compressive strength as high as 380-1085 MPa and forms an integrated micro/macro "high strength-high toughness" fiber-like composite structure (Fig. 4). The study of the micro-deformation mechanism reveals that the precipitation of high-strength compounds effectively prevents cracks from sprouting and expanding in the heterogeneous interface (Fig. 5). Meanwhile, high-resolution observation shows that the Ti 3 Al phase precipitated at the interface forms effective deformation twins inside the grains after deformation (Fig. 7) and improves the coordinated deformation ability between the high-and low-modulus phases precipitated at the interface. This is the main mechanism for the enhancement and toughening of the composite structure. Conclusions By adjusting the vacuum melting temperature, an aluminum/titanium composite structure can be obtained with a dense combination of the interface. The thickness of the reaction-generated interface is approximately 600 pm, and the phase precipitated within the interface is a Ti-Al intermetallic compound with high hardness. The aluminum/titanium composite structure has good strength and toughness, and by adjusting the volume fraction of the titanium alloy skeleton, the macro-strength/toughness of the composite structure can be adapted. The achieved compressive strength varies in the range of 380-1085 MPa, which is 1.4-4 times that of the aluminum matrix (270 MPa). Regarding the pre-fracture elastic deformation, the strain of the composite structure is 3.3%-7.2%, which is 0.6-2.4 times that of the aluminum matrix (2.1%), and a bidirectional prediction model of structureproperty is established. The main reasons for the enhanced toughening of the Al-Ti composite structure are as follows: First, by controlling the reaction temperature, a soft phase and hard phase spatially interpenetrating phase structure is formed in the interface, and this soft/hard zone induces the hetero-deformation induced (HDI) strengthening mechanism under the action of the stress. The Ti 3 Al twins in the interface have certain deformation ability, which further forms a micro/macroscopic interface with a very good match of strength and toughness. Second, geometrically necessary dislocations are formed around the phases with higher modulus precipitated in the interface, which is favorable for the coordinated deformation between the soft and hard phases. It is worth mentioning that the processing method presented in this study can be extended to any metal system with compositions having different melting points, which can provide a theoretical basis for more accurate and efficient design and construction of multimetallic systems.

To address the challenges associated with difficult-to-process and service-failing titanium alloy parts, laser deposition repair technology is employed to restore their dimensions and mechanical properties. Given the heterogeneous microstructure of laser deposition repair parts, significant changes in mechanical properties can occur. To delve deeper into the mechanical properties of laser deposition repair, TA15 titanium alloy spherical powder is used as the raw material to manufacture TA15 titanium alloy plates through forging. Experimental samples are then prepared using laser deposition repair technology, and the impact of different heat treatment systems on the microstructure and mechanical properties of the laser deposition repaired TA15 titanium alloy is investigated. Furthermore, the fracture mechanism under various heat treatment systems is analyzed. The results reveal that the laser deposition repair of TA15 titanium alloy comprises three distinct regions: the wrought substrate zone (WSZ), the heat-affected zone (HAZ), and the laser deposition repair zone (LDRZ). During the structural transformation process, the equiaxed α phase undergoes disruption. DIC results indicate that the LDRZ plays a predominant role in plastic deformation. Thanks to the formation of short rod-shaped α phases in the LDRZ and the precipitation of additional secondary α phases in both the LDRZ and HAZ, the sample subjected to heat treatment at 910 °C/1 h achieves an optimal balance of strength and plasticity.

Laser‐deposition repair technology is employed to repair damaged TA15 titanium alloy forgings. Heat treatment is used to control the microstructure, strength, and plasticity of these repaired forgings. The fatigue properties and crack initiation and propagation characteristics of the repaired parts are studied. Optical microscopy and electron microscopy are used to analyze the microstructure, fatigue fracture, and longitudinal section near initiation. In the results, it is indicated that the tensile and fatigue properties of repaired parts after 900 °C heat treatment are superior to those treated at other temperatures. This is attributed to the strong tissue sensitivity of the repaired specimens’ performance. With increasing heat‐treatment temperature, the secondary α phase in the dimorphic structure tissue thickens. Additionally, the restoration zone develops in layered α phases and becomes truncated, leading to shortening and thickening. The heat‐affected zone undergoes a transformation from a transitional structure to a basket organization. After heat treatment at 1000 °C, the microstructure becomes relatively slender, cracks propagate readily, and the resistance is weakened.

Pores are major cause of fatigue failure in laser-directed energy deposition (L-DED) titanium alloy. For the safe application of L-DED titanium alloys, it is essential to establish a fatigue life prediction method based on pore-induced fatigue. This paper proposes a prior progressive fatigue life prediction framework based on ridge classification and kernel ridge regression algorithms. The fatigue life prediction was carried out on L-DED Ti-6Al-4V alloy in three steps: critical pore identification, fine granular area existence prediction and final fatigue life prediction. The fatigue life prediction method adopted in the current study outperform the others with a correlation coefficient as high as 0.951, followed by a comparison with the results derived from different machine learning algorithms. The results show that the proposed fatigue life prediction framework can predict the fatigue life of L-DED Ti-6Al-4V alloy based on computed tomography tests and microstructure features. Due to its strong generalization ability and effectiveness, the proposed prediction method is expected to be valuable for fatigue-resistant design of L-DED Ti-6Al-4V alloy.

Additive manufacturing (AM) is a reliable technique for constructing highly complex metallic parts. Direct energy deposition (DED) is one of the most common technologies used for AM-printed metal alloys. However, issues such as weak binding, poor accuracy, and rough surfaces still affect the final products. These limitations in the metal-feed DED process indicate that post-processing techniques are required to achieve high quality in terms of both mechanical properties and surface finish. Conventional contact-based post-processing methods have several drawbacks, including difficulties in accessing complex shapes, environmental impact, high time consumption and cost, and health risks for operators. To address these problems and improve surface quality, a laser polishing process has been proposed. By melting or ablating the material with a laser, the laser-polishing process enables the smoothing of the initial topography. It should be noted that there are currently no reviews focusing specifically on laser polishing as a surface treatment technology for the DED process. Therefore, this review presents a unique examination of the mechanisms and primary user-set parameters for both continuous wave (CW) and pulsed laser polishing. The objective is to demonstrate the capabilities of each process and the benefits of using them for the surfaces of DED metal parts. Additionally, existing knowledge and technology gaps are identified, and future research directions are discussed.

The microstructure of Ti-6Al-4V titanium alloy produced by laser additive manufacturing is generally relatively coarse, so its mechanical properties have not yet achieved satisfactory results. After adding germanium element to titanium alloy, second phase particles can be formed, at the same time, due to strong bonding force between Ti and Ge atoms, there also have other strengthening effects that need to be revealed. Therefore, the effect of Ge addition on the microstructure and mechanical properties of additive manufactured Ti-6Al-4V alloy was studied in detail in this paper, which can provide more reference for optimizing the performance of titanium alloy manufactured with additives manufacturing. The pure Ge powder was ball milled with Ti-6Al-4V powder in several different proportions, and bulk samples were prepared by laser deposition manufacturing (LDM) with the mixed powder. The Germanium alloyed Ti-6Al-4V alloy's tensile strength and plasticity at room temperature increased about 25% and 10%, respectively, compared with LDMed Ti-6Al-4V alloy without Ge. According to the results of TEM and EDS, Ti and Ge reacted to form granular second phase Ti 5 Ge 3 , which distributes along the primary β grain boundary inhibit the growth of columnar crystals. Part of Ge solutes into α phase. Both microstructure refinement and solid solution are very effective in impeding the moving of dislocation, so that the Germanium alloyed LDMed Ti-6Al-4V alloy showed excellent tensile property at room temperature.

Pristine polyurea elastomers are usually limited by insufficient strength and lack of functionality. Smart, multifunctional and mechanically resilient nanocomposites were manufactured in this study by compounding functionalized graphene nanoplatelets (F-GNPs) with polyurea via in situ polymerization. This was followed by investigation of the mechanical properties, resistance to chemical media, electrical conductivity and sensing performance of the nanocomposites. A nanocomposite at 0.2 ​wt% of F-GNPs exhibited improvements in tensile strength (60.7%) and elongation (92.1%) as well as obviously enhanced impact performance. The nanocomposite was then investigated as a multifunctional sensor, which exhibited high stretchability with a large workable strain range (5%) and good cyclic stability (9100 cycles). As a temperature sensor, the nanocomposite demonstrated high repeatability and stability in response to cyclic changes from −20 ​°C to 110 ​°C. Its self-sensing capability made possible detecting and tracking its own damage at varying impact levels.

Additive manufactured GH4169 alloy samples were connected by laser deposition manufacturing method in three forms considering directional columnar dendrites, and the effect of different crystal orientations on the connected samples’ microstructure and mechanical properties was investigated. Metallographic analysis shows that the laser deposition connecting (LDC) GH4169 alloy samples presented an obvious directional growth of columnar dendrites at both ends of the fusion line, and small-sized dendrites and equiaxed crystals appear at the fusion line. After heat treatment, the small-sized columnar dendrites were transformed into equiaxed crystals, and the microstructure was similar to that of the deposited state in other regions. The tensile test results show that the connecting properties varied with different connection angles. Heat treatment can modify the tensile properties significantly. The fracture locations of the connection were all in the weaker tensile zone, the parent material close to the fusion line, due to the different crystal orientations. Graphical abstract Set up of LDC angle and corresponding microstructure and mechanical properties

Significance Owing to the continuous developments in the Chinese aerospace industry, aviation structural parts need to ensure lightweight, high efficiency, long flight time, and high maneuverability characteristics. Therefore, it is a significant challenge in structural optimization design to further reduce the structural quality coefficient. Traditional lightweight designs are mostly based on the replacement of classical structures with equivalent parts, such as lean improvement and excavation of structural potential using the new processes and new materials, and have now approached the "ceiling". Topology optimization technology, as an important branch of structural optimization design, determines the optimal material distribution and best load -bearing path by defining material properties, load conditions, and constraints. It is an effective design method for obtaining lightweight structure design and high-performance innovative configurations, and has been widely used in aerospace, automobile manufacturing, and other fields. However, topology configurations are usually complex. Limited by traditional manufacturing processes, designers often need to simplify the optimal topology configurations, which fails to fully reflect the structural advantages of topology optimization design. Additive manufacturing technology uses high-energy laser beams and adopts the superposition mode of "bottom to up" layer -by -layer material melting, which can realize rapid prototyping and solid -free manufacturing of complex topology configurations without molds. This method addresses the problem of "manufacturing determines design" in structure optimization, which greatly broadens the design space. However, additive metal manufacturing technology is not completely a "free manufacturing" technology, and it is limited by unique manufacturing constraints. Therefore, considering additive manufacturing constraints in topology optimization design, researching and developing topology optimization design for additive metal manufacturing has a broad application prospect. Progress This study reviews the progress of structural topology optimization design for metal additive manufacturing technology. First, it summarizes the common methods and characteristics of continuum structure topology optimization (Table 1) and compares the cantilever beam topology optimization results obtained with different methods (Fig. 1). From the perspective of optimizing topology algorithms, it concludes the effective measures to improve structural continuity and manufacturability based on topology optimization methods of elements and boundary evolution (Figs. 2-4). Then, it expounds on the principle, processing characteristics, and application range of the mainstream metal additive manufacturing technology (Fig. 5). After that, it summarizes the topology optimization methods considering the geometric size (Fig. 8), structural forming (Figs. 9 and 10), and material property constraints (Fig. 11) of metal additive manufacturing technology (Fig. 7 and Table 2). Finally, it prospects the development directions of metal additive manufacturing and topology optimization technology. Conclusions and Prospects In this study, the structural topology optimization of an advanced design technology is integrated with the metal additive manufacturing technology that is an advanced manufacturing technology. This study summarizes the methods, characteristics, and improvement measures of continuum structure topology optimization design. Moreover, it expounds on the principle, characteristics, and application of metal additive manufacturing technology. In addition, it summarizes and prospects the topology optimization methods considering the constraints of metal additive manufacturing, which will provide a reference for researchers to further study the topology optimization design for metal additive manufacturing technology. Topology optimization design has shortcomings of numerous design variables, weak convergence, and low computational efficiency. It is often difficult for existing topology optimization algorithms to output the optimal structural performance solution that can be directly used in additive manufacturing. Therefore, combined with the parallel computing technology, it is crucial to carry out algorithm research with fewer design variables and better convergence, and output the optimal solution that can be directly used in additive manufacturing. The research on macroscopic topology optimization and microscopic lattice structure is becoming increasingly improved. By effectively integrating the two, fully leveraging the high-performance configurations of topology optimization design and broad design space provided by additive manufacturing technology, the pursuit of high-performance lightweight design has broad development prospects. The topology optimization methods considering the constraints of metal additive manufacturing adopt relatively ideal material models, which differ from the actual printing materials used in metal additive manufacturing technology. Therefore, establishing a precise topological model of material anisotropy under multiple process parameters, quantification of process parameters of metal additive manufacturing equipment, simulation of the metal additive manufacturing process, and prediction of warping deformation and cracking of parts can effectively reduce residual stress and deformation, and improve forming accuracy and surface quality. Topology optimization design for metal additive manufacturing technology is often based on the optimization of a single material. Effectively combining multi -material topology optimization and metal additive manufacturing, studying the topology optimization design and metal additive manufacturing technology of functional gradient materials, and realizing the integrated design of materials, structure, process, and performance, are breakthrough points in the pursuit of high-performance, multi -function, and lightweight.

Directed energy deposition (DED) is suitable for fabrication of large Inconel 718 components, however, large columnar dendrites and several laves phase impair the mechanical properties. In this work, the formation mechanism of heterostructure microstructure with coarse grain (CG) and fine grain (FG) alternating distribution was explored, and the evolution process of Laves phase during inter-layer hammering hybrid directed energy deposition (HDED) was revealed. The results show that the heterostructure microstructure composed of CG region and FG region with a ratio of 1:1 was obtained due to the work hardening and recrystallization mechanisms, and the average grain size of CG region and FG region are 68.9 mu m and 12.0 mu m, respectively. The Laves phase was first fractured into small pieces by hammering and then resolved into the matrix during the subsequent heat input process, which promotes the precipitation of gamma '' phase from the matrix. The strength and plasticity of the specimens fabricated by HDED are synchronously improved. The dislocation strengthening and solid solution strengthening are the mainly contributions to the strength improvement, and the grain refinement and heterostructure microstructure increased the plasticity of the hybrid manufactured specimens.

整体结构取消连接件与紧固件,将分段机械连接结构变为一体化结构,是飞机结构实现轻量化和长寿命的重要技术途径.由于缺乏整体结构裂纹扩展规律研究和损伤容限设计方法,整体结构应用受到较大限制.针对该问题,基于Franc3D软件对典型整体结构件开展裂纹扩展规律研究,分别研究不同应力水平下裂纹扩展特征与低应力水平下典型整体结构裂纹扩展规律.研究结果表明,应力大小对裂纹扩展寿命影响显著,控制应力水平是确保结构寿命安全的重要手段;在低应力水平下,整体结构裂纹扩展可以分为3个阶段,第1阶段为缓慢扩展阶段,占全寿命周期的94.85％,裂纹穿过十字交叉区出现2次分叉现象.

Fiber metal laminas (FMLs) are disadvantaged by weak interlaminar strength limiting their application where dynamic loads are expected. In this study, graphene platelets (GnPs) were employed to strengthen the inter -laminar interface in carbon fiber (CF) metal laminates. GnPs within range of 0-1 wt% were added into epoxy resin via ultrasonication. GnPs-based FML samples were prepared by wet lay-up method and tested under flexural loading, short beam shear and single lap shear. The reinforcing mechanism and failure modes were investigated. The results show that 0.5 wt% of GnPs increases the flexural strength and interlaminar shear strength by 39.7% and 53.2%, respectively. In addition, molecular dynamics (MD) simulations concluded that the addition of low content of GnPs increases the elastic modulus of the matrix and improves the resin adsorption on the surface of carbon fiber and Al sheets. The results from both the experimental and MD simulation indicate that adding GnPs can effectively improve the interlaminar mechanical properties of FMLs. In principle, the research method in this paper can be applied to the study of FMLs with other nanomaterials.

Objective Due to uneven heating and cooling characteristics, parts accumulate thermal distortions during periodic expansion and contraction during laser deposition. Geometrical defects, such as flatness defects, melting collapse, warping and cracking, seriously affecting the parts' size accuracy. In particular, the warping and cracking of large-scale structural parts can easily cause material wastage and limit the development of laser deposition manufacturing technology. Therefore, realizing the online detection of warping and cracking prediction is an urgent problem for laser deposition manufacturing. In the current research, scholars have utilized digital image correlation technology and laser displacement sensor to monitor the transient strain field, warping and instant cracking. The detection accuracy was also improved by combining it with a machine -learning algorithm. However, while the results show the laws of warping and cracking, the global detection of warping and prediction of cracking have yet to be achieved. This study aimed to realize warping detection and cracking prediction through the changing trend and variation of the warping angle during the deposition process and to improve the forming quality.Methods A warping detection and cracking prediction system were built based on a laser deposition manufacturing system and laser scanner to monitor the surface morphology of parts in real-time. A new algorithm for warping detection and cracking prediction was proposed based on the warping angle and was verified by experiments. First, the surface topography data of the current deposition layer were obtained using a laser scanner, and in -situ detection was realized through morphology reconstruction and hand -eye calibration. The point cloud data were then pre-processed by straight -through filtering, statistical filtering, and bounding box filtering to prepare for surface reconstruction. Next, the warping angle of the intersecting line was calculated using the rotary and parallel slices that vertically crossed the reconstructed surface. Simultaneously, warping threshold Q0 and cracking threshold K0 were set according to the part size and allowable distortion degree. Finally, warping was determined according to whether the warping angle exceeded the threshold Q0, and cracking was predicted by the changing trend of the warping angle and the variation in five consecutive layers (K). Cracking may occur when the warping angle increases and the variation K exceeds the threshold K0.Results and Discussions This study proposes a new warping distortion measurable indicator for laser deposition manufacturing (for the plane), that is warping angle (Fig. 4), which can be used to achieve warping detection and cracking prediction through rotary and parallel slices (Fig. 5). The software framework (Fig. 2) includes three main modules: visualization, system control and data processing, the whole process can be visualized using the PCL point cloud library. The effectiveness of the warping detection algorithm (Fig. 6) was experimentally verified. The experimental results showed that the algorithm could determine the direction prone to warping using rotary slices (Table 1) and conduct complete coverage detection on the surface of the parts (Fig. 10) using parallel slices. When the warping angle of an intersecting line exceeds threshold Q0, a locally accurate judgment is made (Table 2). The cracking prediction algorithm (Fig. 8) was verified experimentally. By calculating the warping angle Q in the cracking influence area and the variation K in five consecutive layers (Table 3), the results for layer 51 indicate that cracking may occur. With continued deposition, three cracks appeared in layer 55. The cracking phenomenon of Ti65 components during the laser deposition manufacturing process was successfully predicted (Fig. 11).Conclusions In this study, a new algorithm for warping detection and cracking prediction based on the changing trend and variation in the warping angle was verified experimentally. The two schemes of rotary and parallel slices have their own characteristics. The former requires fewer calculations and can be used to determine the direction of warping, and the latter has a more comprehensive and uniform detection range and can be used to determine the warping distribution. The warping angle of the intersection lines between the slices and the reconstructed surface was calculated, and warping detection was completed by comparing them with the warping threshold. The maximum warping angle of each layer was recorded, and the changing trend and warping angle in the cracking influence area were combined with the cracking threshold to complete the cracking prediction. The experimental results demonstrated that the proposed algorithm is reasonable, logical, and robust. It can detect warping quickly and effectively and predict the occurrence of cracking. The warping detection and cracking prediction system enhances the quality and process monitoring ability of laser deposition manufacturing and provides essential evidence for process optimization.