Strengthening Process Research Articles

Strengthening behavior and microstructure of 2195 Al-Cu-Li alloy under cycling loading

Cyclic strengthening process, as a newly developed aluminum alloy strengthening technique, has garnered significant attention due to its advantages of rapidity, efficiency, and superior mechanical properties. This study investigated the effects of strain amplitude and loading frequency on cyclic strengthening, including mechanical properties and microstructural evolution. At room temperature, the cyclic strengthening effect of the 2195 alloy increases with increasing strain amplitude, while the influence of loading frequency is pronounced within the elastic range but nearly negligible within the plastic range. Microstructural analysis reveals that cyclic strengthening behavior within the elastic range is attributed to the precipitation of clusters, whereas within the plastic range, it is attributed to the precipitation of clusters and dislocation multiplication. Unlike other plastic deformations, cyclic plastic loading generates dislocations primarily in the form of dislocation loops. The dynamic precipitation of clusters and the diffuse distribution of dislocation loops significantly enhance the alloy's strength with minimal sacrifice of elongation. Experimental investigations on the influence of loading frequency on these precipitation behaviors demonstrate a positive correlation with dislocation generation and a negative correlation with cluster precipitation. Comparison of specimens with different strain amplitudes reveals that larger strain amplitudes provide more energy for cluster precipitation, thereby promoting precipitation. However, excessively large strain amplitudes lead to the annihilation of vacancies due to the introduction of more dislocations, thus inhibiting cluster precipitation. This indicates that the precipitation of clusters during cyclic deformation is profoundly influenced by dislocation behavior. This study deepens the understanding of cyclic strengthening mechanisms and provides support for subsequent development of cyclic strengthening processes in other materials design.

Phase field modeling of fracture mechanics for ion-exchanged glass considering large viscoelastic deformation, mechanic–electrochemical coupling

A phase field model is proposed to investigate the fracture mechanics of ion-exchanged glass, which involves significant viscoelastic deformation and stress-diffusion interaction. Based on this theoretical model, the fracture behavior of both double-sided and single-sided ion exchange processes was studied. The results indicate that, compared to single-sided ion exchange, the double-sided process is more likely to induce crack initiation and propagation, ultimately resulting in a notable reduction in glass strength. For both cases, increasing the glass thickness and interfacial energy density will significantly improve the fracture resistance of the glass. Notably, when the glass thickness or interfacial energy density is large enough, the crack can be completely closed, ensuring the integrity of the glass during the ion exchange process. Furthermore, the study conducted a preliminary investigation of two industrially relevant conditions: edging and impurities. The impacts of edging parameters, glass interfacial energy density, and covering radius on glass stress evolution, mechanical deformation, crack initiation, and crack propagation during chemical strengthening were summarized. These findings offer valuable theoretical support and a reference for optimizing chemical strengthening process parameters and enhancing the strength of glass products.

Formation mechanism of blade surface integrity based on hybrid process of cryogenic minimum quantity lubrication and ultrasonic rolling strengthening process

This study proposes a hybrid process method based on Cryogenic Minimum Quantity Lubrication and Ultrasonic Rolling Strengthening Process (CMQL-URSP) to improve the surface integrity and enhance the mechanical properties of blade surface. First, the principle of the CMQL-URSP hybrid process was described. Second, the TEM experiments were conducted to clarify the influence of the CMQL-URSP hybrid process on aircraft engine blades. Finally, the blade processing experiments were performed to demonstrate the effectiveness of the CMQL-URSP hybrid process on the blade surface micro-morphology, micro-hardness and residual stress. The results indicate that the CMQL-URSP hybrid process effectively overcomes the limitations inherent to the solitary application of URSP. The CMQL process inhibits work hardening, thereby allowing the URSP to achieve better low-plastic surface improvement. Grain refinement governed by the continuous dynamic recrystallization mechanism leads to the formation of nanocrystals, which significantly improves mechanical properties of blade surface. The CMQL-URSP hybrid process results in a reduction in surface roughness from Ra 2.644 μm to Ra 0.055 μm, an increase in surface residual compressive stress from 321 MPa to 657 MPa, and the formation of a reinforced layer with a depth of 3.7 mm on the blade, thereby enhancing the surface integrity of the blade.

Influence of the Vertical Load Bearing Status on the Seismic Performance of Weak-Joint-Type RC Frames Strengthened by the Wing Wall Installation Method

“Strong column–weak beam, strong joint–weak member” is a core concept for the seismic design of buildings. For existing reinforced concrete (RC) frame buildings that do not satisfy this concept, installing RC wing walls beside existing columns is a simple and effective method for strengthening both columns and joints to promote a beam-hinging mechanism. In this study, a numerical simulation method is used to analyze the seismic performance of weak-joint RC frames strengthened by additional wing walls considering the column axial force ratio and to determine whether to consider the secondary load as a variable. The results show that when the secondary load is not considered, i.e. existing columns do not bear a load during the strengthening process, the strength, stiffness and energy dissipation of the structure increase with increasing axial force ratio, but the ductility of the structure decreases. When the secondary load is considered, the strength and initial stiffness of the frame are the greatest when the column axial force ratio is 0.4. When the axial force ratio is less than 0.4, the secondary load has less influence on the strength, stiffness and energy consumption. When the axial force ratio is greater than 0.4, the secondary load has a significant impact on the seismic performance of the strengthened structure, and the strength, stiffness, energy consumption and ductility are significantly greater than those in the case in which the secondary load is not considered. Additionally, the larger the axial force ratio is, the more significant the difference is. It is revealed that in engineering seismic strengthening using the wing wall installation method, the influence of secondary load on seismic performance should not be ignored, especially when the axial force ratio is large.

Efficiency of FRPU strengthening of a damaged masonry infill wall under in-plane cyclic shear loading and elevated temperatures

This paper presents results of in-plane shear tests carried out at the ZAG laboratory in Ljubljana (Slovenia) on a RC frame with masonry infill made of clay blocks (KEBE OrthoBlock). The frame was loaded with constant vertical loads at the top of the columns and then by gradually increasing horizontal cyclic loads at the top beam level. Acquired forces and measured displacements allowed capturing hysteretic behavior for determination of dissipation energy. In addition, two Digital Image Correlation (DIC) systems, Aramis and the CivEng Vision, were used to visualize the behavior of the tested specimens, with an emphasis on computing locally required information about the behavior of highly deformable interfaces. Three types of specimens were tested in-plane: the reference specimen in form of plain RC frame, the reference specimen with constructed masonry infill without any strengthening and the specimen, previously damaged and then strengthened on both sides using glass mesh bonded to the infill and the RC frame using flexible adhesive made of polyurethane matrix (Glass Fiber Reinforced PolyUrethane - GFRPU system). The strengthening process, allowed the specimen to withstand additional cyclic loads, reaching a maximum drift of 3.6 % without serious damage disqualifying the structure from further exploitation. The GFRPU strengthening system was found to be highly effective in preventing infill collapse of damaged masonry infill wall during in-plane loading. Additionally, the results of extended thermal analysis of PU are presented as polymers are, in general, a material, poorly resistant to heat. However, the analyzed PU manifested stable properties up to 200 degrees Celsius, which makes this material promising in civil engineering applications at elevated temperatures.

Peran Bimbingan Konseling Pesantren dalam Meningkatkan Penguatan Karakter Siswa Madrasah Aliyah Baytul Mukarromah Watampone

Islamic boarding school counseling guidance is a form of implementing services provided to help students or santri to develop into individuals who are independent, responsible, creative, productive and behave honestly through character strengthening education. The values that exist in character education are included in Islamic boarding schools' guidance and counseling services. The role of Islamic boarding school counseling is to instill the habit of practicing Islamic teachings in students or santri in daily life through the practice of worship. With program material covering faith, morals and worship. Forming character cannot be done in an instant by giving advice, orders, or instructions, but with the role of the Islamic boarding school guidance and counseling program. The formation of character requires an example, patience, habituation, and repetition. Thus, the process of education and character strengthening will be experienced by students or santri as a form of personality or self-character experience. The values of religious and moral life will strengthen the character of cooperation, time discipline, courage, and confidence in daily activities and learning processes. This is a step to gain knowledge and be able to apply knowledge in the form of skills work and as a positive attitude. From the results of this study, several important things were obtained regarding the role of Islamic boarding schools as a character strengthening program in madrasas. First, helping students or santri in dealing with the problems of everyday life. Second, giving motivation to students or students and teachers in order to build a spirit of enthusiasm for service. Third, implementing the results of coaching as a character education agenda. Meanwhile, based on the role played by a guidance and counseling teacher, namely the planning of Islamic boarding school guidance and counseling services, the implementation of Islamic boarding school guidance and counseling services, and the evaluation of Islamic boarding school guidance and counseling reports. services carried out with Islamic boarding school counseling to students or santri can form a spiritual and emotional soul with moral development as character strengthening.

Tribological and mechanical properties improvement of G20CrNiMo alloy via fabricating gradient composite layer through ultrasonic strengthening grinding process

Fretting wear is one of the main causes of damage failure at the contact interface, which significantly limits the reliable application of mechanical parts. To address this issue, a composite microstructure comprising a gradient structure, α-Al2O3 particles, and micro-dimples was fabricated on the G20CrNiMo alloy by an improved method of ultrasonic strengthening grinding process (USGP). Subsequently, the fretting resistance and mechanical properties of the treated G20CrNiMo alloy were investigated. The results indicated that USGP could significantly enhance mechanical strength and wear resistance properties. The USGP-treated sample demonstrated an increment of approximately 25.32 % in tensile strength compared to the untreated sample. It also exhibited reductions of about 19.61 % and 49.56 % in friction coefficient and wear volume, respectively. After USGP treatment, the gradient structure incorporating dense dislocation and high-angle grain boundaries (HAGBs) limited the shear motion of the G20CrNiMo alloy, thereby enhancing its mechanical properties. Furthermore, the synergistic effect of gradient structure, Al2O3 particles, and micro-dimples effectively restricted shear deformation and formed a supplementary glaze to further improve its fretting wear resistance.

Effect of surface high-density twinned structure on the fatigue crack initiation of Ti–6Al–4V

Fatigue crack initiation sites would transfer from surface to subsurface of metal specimens through shot peening (SP) or laser shock surface strengthening. This phenomenon is typically attributed to the introduction of compressive residual stress on the surface of the specimen during the surface strengthening process. In this study, Ti–6Al–4V specimens featuring a high-density twinned structure on their surfaces, which eliminated compressive residual stress, were fabricated. Fatigue test result revealed that fatigue crack initiation sites in specimens with twinned structures were predominantly located in the subsurface, near the junction area between the twinned structure and the matrix. This phenomenon was accompanied by an increase in fatigue life. The microstructural features in the fatigue crack source were analyzed using focused ion beam (FIB) coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It was observed that primary crack formed in badly oriented grains that are difficult to initiate dislocation slip according to the Schmid factor (SF). Nonetheless, TEM observations revealed the activation of basal <a> dislocations in these grains, potentially leading to crack nucleation along basal slip bands and subsequent propagation along the basal plane. Our results suggest that a high-density twin structure on the surface can enhance the fatigue strength of Ti–6Al–4V by transferring the fatigue crack source to the subsurface.

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

Experimental Investigation of Rotational Behavior of Glulam Column-Beam Connection Reinforced with Carbon, Glass, Basalt and Aramid FRP Fabric

In the domain of modern timber structural systems, timber frame constructions distinguish themselves as preferred and commonly used building methods. Their appeal arises from their architectural adaptability and their distinctive attributes, which enable rapid assembly. In this type of structural system, the effectiveness of the connections between beams and columns plays a pivotal role in determining how forces are distributed, ensuring lateral stiffness, and upholding structural safety. Various methods have been developed to ensure column-beam connections in wooden structures. Column-beam connection points deteriorate and get damaged over time. These critical areas need to be strengthened over time. In this study, glulam columns (140 mm &amp;times; 140 mm) and beams(140 mm &amp;times; 280 mm), which are often used as load-bearing elements in wooden structures, were used. Columns and beams are connected to each other according to the wooden notching method. Column-beam connection areas are reinforced with carbon, glass, basalt and aramid fiber reinforced polymer fabrics. After the strengthening process, bending tests of the column-beam connection samples were carried out and the load carrying capacity, total amount of energy consumed, and maximum stiffness values were determined. Additionally, FRP damages occurring in the column-beam connection areas were observed during the experiments. The optimal outcomes for encasing column-beam connections have been identified with carbon-based fiber reinforced polymers. Glassbased fiber reinforced polymers yielded the least favorable results. Aramid-based fiber-reinforced polymers demonstrated similar outcomes to those wrapped with carbon-based counterparts. Consequently, it can be deduced that reinforcing column-beam connections with FRP fabrics, be they carbon, aramid, basalt, or glass-based, can markedly enhance their strength and durability, thereby extending their operational lifespan.

Enhanced strength–ductility synergy in Ti55531 titanium alloys through gradient microstructural design strategy

The strength-ductility trade-off dilemma still exists for titanium alloys, which is a challenging and pressing issue within the realm of microstructure design and property control. In the present work, a typical axial gradient microstructure was prepared in Ti55531 titanium alloy through a composite strengthening process involving rapid electropulsing treatment (EPT) combined with step-quench treatment (SQT). The results show that a significant improvement of 450 MPa (54 %) and 6.3 % (100 %) for the strength and ductility are obtained respectively for gradient microstructure by EPT + SQT (GMES) compared to that gradient microstructure prepared by EPT (GME) only. This indicates that the enhanced strength-ductility synergy observed in GMES is attributed to the characteristic Twinning induced Plasticity (TWIP) mechanism employed in this novel design of gradient microstructure. Furthermore, a detailed analysis and discussion are provided on the physical deformation mechanism and crack initiation behaviour of the gradient microstructure, providing valuable insights for the design of high-strength, high-ductility metals such as beta titanium alloys, advanced steels, and multi-phase alloys.

Dual-scale reinforcement of co-cure single lap joints through graphene nanoparticles and CFRP Z-pin

This study presents the report of the dual scale strengthening process to the co-cure (CC) single lap joint (SLJ) reinforced by Graphene nanoparticles (GNP) and carbon fiber reinforced polymer (CFRP) Z-Pin. The shear test indicated that inner and outer reinforcing with GNP in adhesive and Z-pin in SLJ improved shear properties. The combined reinforcement of GNP and 90°/Z-pin enhances shear strength under static loading with 99.89% compared to plain epoxy CC SLJ. After testing, microscopic images of the fractured specimen surface were used to investigate failures. The fractography studies reveal that adding GNP to the adhesive and Z pin in SLJ roughens the surfaces, strengthening adhesive-adherend contact.

საავტომობილო გზის მიწის ვაკისისა და საფუძვლის გაძლიერება დოროსოლისა და დოროპორტის გამოყენებით

Road construction is the main determining part of the transport and operational condition of highways. The improvement of the road surface with the use of hydraulic binders under the conditions of minimum costs is discussed. The physical-mechanical parameters of soils are examined, as well as the issues of deformation of layers and a higher modulus of elasticity, which all contribute to enhancing the quality and durability of road construction. Details on the advantages of using hydraulic road binders, Dorosol and Doroport in the soil strengthening process are provided. Financial costs and terms for road construction are compared and calculated, and the differences between soil consolidation using new hydraulic road binders and Portland cement are evaluated. In addition, the article concentrates on the challenges of reducing the following negative impact on the ecology and the environment by strengthening soils with hydraulic road binders, with economical use of water and natural resources.

Study on the repair behavior of passive film of iron-based amorphous coatings by eco-friendly phosphate inhibitors

The passivation ability of the coating can be improved by adjusting the elements proportion in the Iron-based Amorphous Coating and the spraying process, but the process is complicated and costly. In this study, it was found for the first time that Iron-based Amorphous Coatings can quickly form passive films in phosphate atmosphere, which simplifies the coating strengthening process. Electrochemical measurements, XPS, AFM, FTIR, and SEM-EDS were used to investigate the inhibition mechanism of eco-friendly phosphates on the dynamic dissolution of passive film of Fe-based amorphous coating. When the coating was soaked in 3.5 wt% NaCl + 0.1 M solution, the iron phosphate compound on the coating surface promoted the repair and growth of the passive film, and the film thickness increased by more than 32.9 %. The increase of Fe2+/Fe3+ and (O2-+H2O)/OH- in the passive film means that more insoluble Fe-Cr compound growth significantly reduces the donor density (Nd) in the passive film and inhibits the degradation rate of the passive film in the corrosive environment.

An experimental and numerical study on two-way RC slabs with openings strengthened by ferrocement technique

This study investigates the impact of creating a central square opening on reinforced concrete slabs and assesses the strengthening process using ferrocement layers. The investigated key parameters were the opening sizes, type, number, and extension length (outside the opening sides) of steel mesh layers used to strengthen the tested slabs. The experimental program included the preparation and testing of twelve two-way reinforced concrete slabs with identical dimensions, thickness, and reinforcement, but were different with respect to opening sizes and strengthening schemes. Four slabs acted as control specimens without strengthening; one was solid; the other three had different opening sizes; and the other eight slabs were strengthened using a ferrocement layer of 2 cm thickness applied on the bottom of the slab around the openings with various reinforcement schemes which included the number, type, and extension length (outside the opening) of steel mesh. All slabs were supported along the four sides with a clear span of 1 m in both directions and tested under four-point loading. The test results demonstrate that creating an opening in the slab decreases the ultimate load by 21.5 %, 31.9 %, and 40.7 % for opening dimensions (15, 25, and 35 cm), respectively. Using the ferrocement strengthening method helps to increase slabs’ flexural load-carrying capacities and reduce crack propagation from opening corners. The study found that strengthening specimens with opening sizes of 15, 25, and 35 cm increased their flexural load-carrying capacities by 26 %, 33 %, and 34 %, respectively. The expanded steel mesh type also resulted in a higher ultimate load by 6–7 % than the welded mesh type. When the length of the strengthening ferrocement layers was doubled, the ultimate load went up by 6–7 %. Increasing steel mesh layer numbers from 1 to 4 increased the ultimate load by 25 % to 40 % compared to the corresponding un-strengthened slab with an opening. The maximum load of a slab with an opening was achieved by applying a 2 cm thickness of ferrocement layer reinforced with expanded metal mesh, with extension lengths equal to the opening's length. The study utilizes commercial software ABAQUS for finite element analysis (FEA) to validate the experimental results, resulting in a great agreement between the analysis and the experimental findings.

The impacts of cover crop mixes on the penetration resistance model of an Oxisol under no-tillage

Soil penetration resistance is used as an indicator of mechanical resistance to root growth into the soil matrix. However, penetration resistance measured only under wet soil conditions may not identify the effects of cover crops on soil structure. We aimed to determine the impact of individual and mixes of cover crops on soil penetration resistance as a function of water content and bulk density in an Oxisol under no-tillage in southern Brazil. Six treatments of individual and mixed cover crops were tested: (i) black oat; (ii) ryegrass; (iii) forage radish; (iv) wheat; (v) Fibrous-rooted crop mix: with 80 % fibrous-rooted and 20 % tap-rooted plants; and (vi) Tap-rooted crop mix: 40 % fibrous-rooted and 60 % tap-rooted plants. Soil cores were collected from a depth of 0–0.10 and 0.10–0.20 m and soil penetration resistance was evaluated under four soil water matric potentials (−6, −33, −100, and −500 kPa). Soil penetration resistance (Q) data for each treatment were fitted as a function of bulk density (ρ) and water content (θ) [Q=f(ρ, θ)]. The soil penetration resistance model was a non-linear equation (i.e., a double power function, with a negative exponent for water content and a positive exponent for bulk density). Under a given combination of bulk density and water content values, soil penetration resistance was higher after single crops than crop mixes, indicating a crop-mediated soil strengthening process. The cover crop mixes increased the macroporosity, resulting in an adequate soil physical quality for successional crops such as soybean, although no differences were observed for cover crops at soil water matric potentials of −60 hPa and −330 hPa when soil penetration resistance was used as a static measurement. The modelling of the soil resistance to penetration, as a function of soil bulk density and soil water content, showed that cover crops changed soil cohesion and reduced the impact of drying on soil strength when compared to the single cropping systems, indicating that soil penetration resistance should be modelled under a broad range of water contents, instead of only under a specific soil water content, to quantify the impacts of cover crops on soil strength.

Investigation of Residual Stress Distribution and Fatigue of 7050-T7451 Alloy Hole Components with Laser Shock and Ultrasonic Extrusion

Small-hole structures, such as the millions of fastener holes found on aircraft, are typical stress-concentration structures prone to fatigue failure. To further improve the strengthening process of this small-hole structure, we make up for the limitations of laser shock processing (LSP) of small holes by combining it with the ultrasonic extrusion strengthening (UES) process to form a new strengthening method—laser shock and ultrasonic extrusion strengthening (LUE). The influence of the LUE process sequence and process parameters on residual stress distribution was studied through FEM, and the gain of fatigue life of specimens after LUE strengthening was also explored through tests. The results show that when using LUE technology, the friction force decreases with the increase in amplitude and decreases by 3.2% when the amplitude is maximum. The LUE process eliminates the thickness effect generated by LSP, which can achieve good stress distribution of small-hole components under smaller laser shock peak pressure, and reduces equipment power. LUE can significantly improve the fatigue life of small-hole components, and the maximum fatigue life gain can be up to 310.66%.

Temperature control research for laser-induction hybrid strengthening process

Temperature control research for laser-induction hybrid strengthening process

Frost resistance and damage evolution model of basalt fiber-reinforced recycled concrete based on recycled coarse aggregate strengthening and vibration mixing processes

A self-created grinder machine was utilized to clear the wrapped mortar from recycled coarse aggregates (RCA) in order to enhance the performance of basalt fiber-reinforced recycled aggregate concrete (BFRAC). In combination with the RCA strengthening and vibration mixing processes, the mechanical properties and freeze-thaw frost of BFRAC were tested to clarify the mechanism for improving the frost resistance under the synergistic effect of basalt fiber (BF) reinforcement and vibration mixing. Meanwhile, the impact of the production process and BF strengthening technique on RAC performance was explained from a microscopic standpoint using a scanning electron microscope (SEM) test, and aggregate-old mortar interface transition zones were significantly reduced. BF is beneficial in improving the mechanical properties and frost resistance of recycled aggregate concrete (RAC). Among them, the performance improvement effect of RAC is the most significant when using vibration mixing processes, adding BF with a length of 18 mm and a content of 0.2 %. It can increase the compressive strength of RAC by 19 % compared to ordinary mixing, the splitting tensile strength by 37.6 %, and the flexural strength by 34.4 %. A polynomial damage deterioration model was established with relative dynamic elastic modulus and compressive strength as damage variables. The results show that the model can accurately predict the degree of freeze-thaw damage of BFRAC. The research results have significant theoretical value for enhancing the frost resistance performance of RAC.