Diesel engine failures have been extensively investigated. However, research specifically addressing failures of roller diesel engines operating under harsh and variable conditions remains limited. This study reports a case of piston assembly-cylinder liner failure in a heavy-duty roller diesel engine that recurred eight years after a major overhaul. The aim is to identify the root causes of failure to prevent engineering delays and economic losses. Unlike previous studies that focused on isolated components, this work conducts a comprehensive investigation covering the piston body, piston rings, piston skirt, connecting rod bearings, and cylinder liner. To elucidate the failure modes and mechanisms, multiple experimental analytical methods were employed, including metallographic examination, chemical analysis, visual inspection, and scanning electron microscopy. The results reveal that the failure was jointly driven by a triggering mechanism (insufficient maintenance), a dominant mechanism (abrasive and adhesive wear), and several secondary mechanisms including corrosive wear, cavitation erosion, and fatigue spalling. Finally, we have proposed targeted corrective actions and maintenance recommendations to prevent recurrence of such failures. The article should be of broad interest to the global engineering community, as early failure of construction machinery remains a critical concern.

Carbon fiber reinforced polymers (CFRP) are widely recognized for their exceptional strength-to weight ratio, making them ideal for advanced applications requiring superior mechanical performance and low weight. However, their heterogeneous composition poses challenges in both processing and surface treatment, which are crucial to improve the strength of bonded joints involving CFRP adherends. Laser processing technology offers several advantages in the processing of CFRPs, such as the effective removal of contaminants (e.g. mold release compounds) which hamper adhesion to structural adhesives. In this work, a UV picosecond laser is used to perform surface preparation of CFRP compression molding laminates. The proposed treatment not only cleans the matrix of release agents but also enables selective matrix removal without damaging the carbon fibers. Pre- and post-treatment surface morphology and chemistry are analyzed using a stereomicroscope, a digital microscope, a scanning electron microscope, and X-ray spectroscopy. The results are an improvement in the ultimate tensile strength of CFRP/CFRP single lap joints by more than 300

GH4169 coatings produced by laser cladding are commonly used in high-temperature applications. However, during the rapid solidification process, deleterious Laves phases form in these coatings, which significantly diminish their mechanical properties and indirectly affect their wear resistance. To address this, GH4169 superalloy with 3 % Vanadium content was developed to alter the segregation of Nb elements and reduce the formation of harmful Laves phases. The study aimed to evaluate how heat treatment affects the mechanical and tribological properties of GH4169/V coatings. After applying a low-temperature solid solution followed by double aging heat treatment, S-phases formed separately while gamma ' and gamma"phases appeared in the gamma matrix of the coatings. This treatment led to a significant increase in average microhardness, i.e., about 69 %. Additionally, tensile strength increased from 804 MPa to 1070 MPa (+40 %), while elongation at fracture decreased from 20.6 % to 14.4% (-30 %). The tensile fracture mechanism shifted from ductile to a combination of plastic and brittle fracture. The maximum shear force at fracture improved from 35.60 kN to 53.4 kN, and shear strength increased by 50 %. Post-standard heat treatment, the coating exhibited a reduced coefficient of friction across various temperatures (200 degrees C, 400 degrees C, 600 degrees C). At lower temperatures (25 degrees C, 200 degrees C), the wear rate increased, whereas, at higher temperatures (400 degrees C, 600 degrees C), it decreased. The superior tribological properties of the GH4169/V coating, both before and after heat treatment at 400 degrees C and 600 degrees C, are attributed to the formation of a continuous oxide film. Moreover, the precipitated reinforcing phases from heat treatment enhanced the coating's hardness, further improving its wear resistance at high temperatures.

In recent years, thermoplastic polymers and composites have seen increasing application across various industrial sectors to develop lightweight structures. These materials have gained popularity in the market due to advancements in additive manufacturing. Thermal direct joining serves as an effective solution for integrating such thermoplastic materials into existing or de-novo metal structures. This method enables the creation of lightweight and virtually reversible joints, which foster end-of-life recyclability, thus aligning with the principles of a circular economy. However, these joints are still affected by a low strength, which is mostly related to the poor polymer–metal interaction. The use of surface treatments that promote mechanical interlocking of the polymer within surface asperities in the mating metallic adherend can be an effective strategy to enhance the strength, as well as to improve the toughness and damage tolerance of the joints. In this work, a laser treatment was used to modify the surface texture of an aluminum sheet prior to thermal bonding with 3D-printed polylactic acid (PLA). Different surface textures were analyzed by modifying the main process parameters. Roughness and wettability measurements were performed to identify the most effective processing condition. Finally, mechanical tests were performed to verify the improvement in joint resistance obtained by interface modification.

In this work, the influence of laser power (LP), scanning speed (SS), and powder feeding speed (PF) on the porosity, dilution, and microhardness of lightweight refractory high-entropy alloy (RHEA) coatings produced via laser cladding (LC) was investigated. Variance analysis (ANOVA) was deployed to ascertain the effect of LP, SS, and PF on performance metrics such as porosity, dilution, and microhardness. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) was then applied to optimize these processing parameters to minimize porosity, achieve suitable dilution, and maximize microhardness, enhancing the mechanical properties of RHEA coatings. Finally, machine learning models—Random Forest (RF), Gradient Boosting Decision Tree (GBDT), and Genetic Algorithm-enhanced GBDT (GA-GBDT)—were developed using orthogonal experimental data, with GA-GBDT demonstrating superior predictive accuracy. The proposed approach integrates statistical analysis and advanced ML techniques, providing a better understanding into optimizing LP, SS, and PF for improved RHEA coatings performance in industrial applications, thereby advancing laser cladding technology.

Interfaces play a critical role in modern structures, where integrating multiple materials and components is essential to achieve specific functions. Enhancing the mechanical performance of these interfaces, particularly their resistance to delamination, is essential to enable extremely lightweight designs and improve energy efficiency. Improving toughness (or increasing energy dissipation during delamination) has traditionally involved modifying materials to navigate the well-known strength-toughness trade-off. However, a more effective strategy involves promoting non-local or extrinsic energy dissipation. This approach encompasses complex degradation phenomena that extend beyond the crack tip, such as long-range bridging, crack fragmentation, and ligament formation. This work explores this innovative strategy within the arena of laminated structures, with a particular focus on fiber-reinforced polymers. This review highlights the substantial potential for improvement by presenting various strategies, from basic principles to proof-of-concept applications. This approach represents a significant design direction for integrating materials and structures, especially relevant in the emerging era of additive manufacturing. However, it also comes with new challenges in predictive modeling of such mechanisms at the structural scale, and here the latest development in this direction is highlighted. Through this perspective, greater durability and performance in advanced structural applications can be achieved.

Inconel 718 alloy (IN718) is a popular choice for aerospace hot-end components due to its exceptional mechanical properties. This study investigates the impact of processing parameters (i.e., laser power, powder feeding rate, and scanning speed) on the microhardness, bond strength, and tensile strength of layer-cladded IN718. The results show that IN718 coatings have high microhardness (277.15 HV0.1), strong metallurgical bonding strength (33.97 kN), substantial yield strength (794.09 MPa), impressive ultimate tensile strength (1171.81 MPa), and notable elongation at failure (8.24 %) under laser power is 1.2 kW, powder feeding rate is 250 mg/s, and scanning speed is 4.5 mm/s. In particular, decreased laser energy input enhances microhardness, yield strength, and ultimate tensile strength but reduces bonding strength and elongation. This is attributed to improved Nb element segregation, the reduction of the Laves phase, and grain refinement. However, inadequate energy input leads to cracks and unmelted powder, negatively affecting metallurgical bonding strength. The shear and tensile fracture mechanism of the IN718 coatings is a typical ductile fracture with a microvoid accumulation fracture. The study can facilitate the fabrication of the IN718 coatings with the excellent mechanical properties and the applications in the engineering field.

The confined build space of 3D printers often necessitates breaking down larger objects into sub-components for efficient printing. Addressing this challenge, related existing research emphasizes the growing adoption of structural adhesives as a key method for joining 3D printed components. In this context, the present study combines finite element modeling, design exploration, and additive manufacturing, to ascertain the role of the adherends’ architecture on the mechanics of crack growth in adhesive bonded 3D printed materials. Finite element simulations and experiments are carried out using Double Cantilever Beam (DCB) specimens comprising epoxy-bonded selective laser sintered polyamide (PA). In particular, the study includes adherends that feature either sub-surface hollow channels of various shapes (bulk patterns) or sinusoidal interfaces with different aspect ratios (surface patterns). The objective is to demonstrate how the proposed patterning strategies not only promote crack shielding and delayed growth but also unlock energy-absorbing processes, such as interfacial void growth and buckling, that are absent in the control joint (i.e., no patterns). Therefore, customizing the architecture of the adjoined layers ultimately results in toughening and enhanced damage tolerance in adhesive joints that comprise 3D printed materials.

Laser cladding is a highly effective technique used in additive manufacturing to enhance the surface properties of workpieces. It is employed to improve wear resistance, corrosion resistance, and high-temperature resilience of materials. This study explores the utilization of laser cladding technology to repair the surface of AISI A2 tool steel by applying a coating of M2 steel. Sixteen experiments were designed using an orthogonal methodology to investigate the intricate relationship between various processing parameters, including laser power, scan speed, powder feed rate, and overlapping ratio. These parameters were examined in conjunction with key mechanical properties of the coating, such as micro-hardness, friction-wear characteristics, and shear bond strength.Additionally, analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) were employed to gain insights into the microstructure of the coatings and elucidate the underlying failure modes. Shear testing of the coatings indicated a tendency towards a brittle fracture mode within the coating, with the dominant wear mechanism involving a combination of abrasive and oxidative wear.Finally, a TOPSIS-Grey Relational Analysis (GRA) method was utilized to identify the optimal process parameters. These optimal parameters were determined to be a laser power of 1200 W, a scan speed of 5 mm/s, a powder feed rate of 14 g/min, and an overlapping ratio of 30 %. Subsequent validation experiments carried out with these parameters demonstrated superior performance compared to the optimal group identified in the orthogonal experiment.

Laser cladding, an innovative surface modification and coating preparation process, has emerged as a research hotspot in material surface modification and green remanufacturing domains. In the laser cladding process, the interaction between laser light, powder particles, and the substrate results in a complicated mapping connection between process parameters and clad layer quality. This work aims to shed light on this mapping using fast evolving machine learning algorithms. A full factorial experimental design was employed to clad Inconel 718 powder on an A286 substrate comprising 64 groups. Analysis of variance, contour plots, and surface plots were used to explore the effects of laser power, powder feeding rate, and scanning speed on the width, height, and dilution rate of the cladding. The performance of the predictive models was evaluated using the index of merit (IM), which includes mean square error (MSE), mean absolute error (MAE), and coefficient of determination (R ^2 ). By comparing the performance of the models, it was found that the Extra Trees, Random forest regression, Decision tree regression, and XGBoost algorithms exhibited the highest predictive accuracy. Specifically, the Extra Trees algorithm outperformed other machine learning models in predicting the cladding width, while the RFR algorithm excelled in predicting the associated height. The DTR algorithm demonstrated the best performance in predicting the cladding dilution rate. The R ^2 values for width, height, and dilution rate were found to be 0.949, 0.954, and 0.912, respectively, for these three models.

The use of polymers in the transportation industry represents a great opportunity to meet the growing demand for lightweight structures and to reduce polluting emissions. In this context, additive manufacturing represents a very effective fabrication route for mechanical components with sophisticated geometry that cannot be pursued by conventional methods. However, understanding the mechanical properties of 3D-printed polymers plays a crucial role in the performance and durability of polymer-based products. Polyamide is a commonly used material in 3D printing because of its excellent mechanical properties. However, the layer-by-layer deposition process and ensuing auxiliary steps (e.g., post-processing heating) may affect the microstructure and mechanical properties of 3D-printed nylon with respect to the bulk counterpart. In this work, we explore the effect of displacement rate and heat exposure on the mechanical properties of 3D-printed polyamide (PA12) specimens obtained by selective laser sintering (SLS). Moreover, the thermal characteristics of the powders and sintered material were evaluated using differential scanning calorimetry (DSC). Our results highlight the expected rate dependency of mechanical properties and show that a post-processing heat treatment partly affects mechanical behavior.

The adherends notching technique has been the subject of a few recent studies and consists of tailoring the geometry of the adjoined layers to mitigate the bondline peak stresses and enhance the joint strength. In the present study, we explored the effect of the adherends notching technique on crack propagation using finite element (FE) simulations based on the cohesive zone model (CZM) of fracture. Double cantilever beam (DCB) adhesive joints subjected to quasistatic loading were considered as a model material system. An array of equally spaced notches was placed on the faying sides of the adherends, oriented perpendicularly to the direction of crack growth. A parametric investigation was carried out to ascertain the role of the notches and the input cohesive properties on various performance metrics, e.g., load-displacement response and dissipated energy. The proposed notching strategy promotes an unstable crack pinning/depinning process, which effectively delays crack growth and increases the effective work of fracture. Additionally, we found that the overall behaviour is tunable by changing geometric (i.e., notch spacing and depth) and bondline material properties.

The primary objective of this research is to investigate the mechanical and tribological characteristics of thin coatings that consist of graphite-like carbon (GLC) and chromium nitride (CrN). The incorporation of GLC and CrN coatings offers a synergistic effect by leveraging the wear-resistant properties of CrN and the low-friction and lubricating properties of GLC. Unbalanced closed-field magnetron sputtering was employed to deposit CrN/GLC coatings onto SDC90 steel. The microstructure, mechanical, and tribological properties of the coatings were comprehensively studied and compared. From the Raman, the ID/IG of the GLC coatings improved from 1.7 to 2.7 by changing the GLC coating thicknesses from 0.2 to 2.0 μm. The records displayed that changing the GLC coating thickness of the CrN/GLC coating can reduce the surface toughness, adhesion strength, and critical loads (the critical loads of S1 and S2 > 40 N, the critical load of S3 < 30–40 N). On the contrary, by changing the GLC coating thickness, the elasticity modulus (from 144.88 to 169.60 GPa), hardness (from 10.27 to 14.32 GPa), and tribological properties of the coatings were positively affected. Regarding the impact friction and wear behavior, the thicker GLC coatings show excellent properties with a lower wear volume and wear rate. The knowledge acquired about the GLC coatings can be utilized to enhance the impact friction and wear of the cold work die steels.

The present work addresses the mechanical performance of adhesive bonded composite/metal T-joints comprising a CFRP skin bonded to an aluminum (AA5754) stiffener. Prior research on the subject has shown that the structural performances of T-joints can be enhanced by a variety of methods, including stitching and z-pinning. Here we propose an alternative approach that does not compromise the integrity of the skin, as it only relies on tailoring the architecture of the stiffener. Our results show that using corrugated flanges with a square wave profile, superior performances, i.e., ＋65% pull-off strength and ＋416% absorbed energy, can be achieved with respect to the conventional configuration.

We investigate the mechanics of crack propagation inarchitectedadhesive joints whose adherends are inspired to the base plate ofthe barnacle Amphibalanus (=Balanus) amphitrite, and feature an array of buried hollowcylindrical channels located perpendicularly to the direction of crackgrowth. Selective laser sintering is used to obtain the adherendsthat are subsequently bonded in the double cantilever beam configurationto ascertain the mechanics of crack growth. Finite element (FE) simulationsare deployed to determine the strain energy release rate (ERR) andto elucidate the salient features of the fracture process. It is shownthat the channels induce a modulation of the ERR and enable a cracktip shielding mechanism. Besides, FE simulations based on a cohesivezone approach indicate the occurrence of crack pinning/depinning cyclesthat are validated via experiments. A highlight of the present studyis the use of a mechanoluminescent (ML) coating to unravel the evolutionof the transient stress field in the crack tip region. The coatingcomprises an optical epoxy resin loaded with doped strontium aluminatephosphors (SrAl2O4/Eu2+) and convertsmechanical energy into light emission with intensity proportionalto the magnitude of mechanical stress. By combining the ML emissionpatterns with the stress distribution obtained from FEA, we unveilinteresting details of snap-through cracking in architected bio-inspiredadhesive joints.

Joining and welding using a nanothermite is a matter of exercising control to introduce the energy needed to perform the weld at a required rate and duration sufficient to reach the joining location and produce the required phase change. This focus is the main drive herein with key properties of exothermic joining/welding discussed from the two perspectives of having the energetic source located internally or externally to the joint. Further works on reactive bonding are also investigated, and some emerging applications are discussed, as well as limitations of current solutions summarily presented, and future development potential is provided as closure.

As the demand for structural light-weighting continues to rise, so does the interest in bonding with structural adhesives. However, adhesive joints are subjected to the nucleation and growth of cracks, and there is a growing need for toughening strategies that can prevent catastrophic failures. This work focuses on secondary bonded composite/metal joints and explores a toughening approach enabled by a snap-through cracking process. A composite flat panel is bonded with a corrugated aluminum substrate with a square-wave profile, whose geometry is defined by grooves' spacing, depth, and width. These key geometrical parameters provide opportunities to tailor the mechanics of crack growth and were chosen by resorting to finite element simulations with cohesive elements. The computational results are validated by experiments that systematically show the occurrence of snap-through cracking and a significant enhancement of load bearing capacity and dissipated energy (up to 260%) compared to adhesive joints without corrugation.

Ensuring the progressivity of failure of adhesively-bonded composite joints is necessary to guarantee safety and to optimize maintenance operations. In our previous work, we proposed a novel surface patterning strategy to stop crack propagation by triggering bridging of adhesive ligaments. However, the brittle failure of classical bridging ligaments still releases a large amount of stored elastic energy, leading to a snap-slip crack propagation or even catastrophic sudden fracture of bonded joints. Such technology could be further improved by integrating ductile structures within the adhesive layer, but the detailed failure mechanisms require systematic investigation. In this work, we integrated thermoplastic polyamide structures within the epoxy adhesive layer of double cantilever beams to guide this transition from brittle failure to a stable softening behavior. Weak polyamide/epoxy adhesion and their embedded area fractions were critical since they affected the damage mechanisms and determined energy dissipation within bonded joints.

A considerable weight reduction in thermoset-based composite is attained by replacing mechanical fasteners with a structural adhesive during the secondary bonding. The quality of this adhesively-bonded joint greatly depends on the surface preparation strategies applied to the mating composites as they influence the surface morphology, topography, interface composition, and mechanical performance of the adherend–adhesive interphase. We reviewed the recent progress of surface preparation strategies generally employed for the aerospace or automotive-grade thermoset composites (carbon/epoxy and glass/epoxy). Then, we briefly reviewed the role of each of them in promoting adhesion mechanisms, i.e., mechanical interlocking, adsorption/chemical bonding, and diffusion. Subsequently, we analyzed qualitatively and quantitatively the effects on indicators associated with surface characteristics of the treated surface and mechanical performance metrics. Finally, we discussed two emerging solutions, namely substrate patterning, and adhesive tailoring. Our analysis shows that creating heterogeneity in the composite adherends or adhesive enables effective tuning of the joint performances.