Compressive Surface Research Articles

Enhancing coercivity and mechanical strength of sintered Nd-Fe-B magnets by heavy rare earth-free grain boundary diffusion

In addition to magnetic properties, mechanical strength is also an important factor in the stability of Nd-Fe-B magnets during service. Here, we proposed a strategy to simultaneously enhance magnetic and mechanical properties by grain boundary diffusion (GBD) without using heavy rare earths (HRE). For a 4.5 mm thick sintered magnet, the coercivity of Pr70Al20Cu10 and Al75Cu25 (at.%) diffused magnets can enhance from 1000 to 1346 and 1089 kA/m, respectively, due to the formation of continuous grain boundary (GB) layers for magnetic decoupling, respectively. The increased compressive strength and surface hardness of the magnet mainly result from the enhanced connection between 2:14:1 grains. Since the diffusion of HRE-free alloys improves GB phase by both increasing the wettability of GB phase and reducing the defects at the interface of 2:14:1 phase, more energy is required for the crack propagation which results in an increase in mechanical properties. Furthermore, this work generalizes the difference between the HRE and non-HRE diffusion sources in enhancement mechanisms of coercivity and mechanical strength. It is thus believed that GBD can be used to improve not only magnetic properties but also the other properties of magnets.

Comparison of the unstart/restart processes of a two-dimensional twin-duct supersonic inlet induced by the plug throttling and thermal choking at the sideslip state

It is of great significance to study the hysteresis phenomenon in the unstart/restart process of supersonic inlets for restart control in the practical operation of ramjet engines. In this paper, the unsteady numerical simulations are conducted for the unstart/restart processes of a ramjet engine with a two-dimensional twin-duct inlet configuration under asymmetric incoming-flow conditions (Ma0 = 2.6,β = 2°), and the unstart/restart characteristics of the inlet caused by the plug throttling and the thermal choking are compared and analyzed. The results show that from the perspective of source incentives, the hysteresis loop of the restart process of the leeward inlet caused by the thermal choking is larger than that of the restart process of the leeward inlet caused by the plug throttling, which indicates that it is difficult to verify the restart performance of the ramjet with the two-dimensional twin-duct inlet configuration in the actual operating process by the inlet's plug-throttling experiment in the conventional wind tunnel. In addition, in the practical operations, the increase of fuel gas causes the transition of the leeward inlet to the unstart state, and part of the fuel gas reacts and combusts stably on the external compression surface of the leeward inlet, which easily leads to the burning of the inlet if there is without any special thermal protection.

The role of bentonite in two-component grout: A comparative study

Two-component grout is the most used backfilling technology in shielded mechanised tunnelling. Bentonite is an important ingredient in the production of component A, since it plays a key role in the mortar stabilisation. Furthermore, recent studies have highlighted its involvement in the mechanical and elastic performance of the hardened grout after short curing times, while no information is available for long curing times. This study proposes an innovative test campaign, based on a comparison between a standard two-component grout mix design (reproduced with 5 different bentonites) and a special mix design, produced without using the bentonite. This interesting comparison highlights the important role of the bentonite and its activation time in properties related to fresh grout (component A) and hardened grout. Assessments of bleeding, viscosity, unit weight, gel time, surface compression strength (SCS), uniaxial compression strength (UCS) and tensile strength (T0) have permitted a deep quantitative analysis that, undoubtedly, highlights the importance of bentonite in this widespread backfilling grout technology.

Mechanism Study of Stress Corrosion Behavior under Tensile and Compressive Stresses for Welded Joint Used in Nuclear Turbine Rotor.

Stress corrosion damage containing pitting and cracking was investigated for NiCrMoV steel-welded joint used in nuclear turbine rotor in 3.5% NaCl solution. The U-bend specimen containing tensile face and compressive face was adopted which was conducive to study the effects of stress on pitting and stress corrosion cracking. On tensile surface of U-bend specimen, pit grew in open environment and was converted into crack covered with passivated film. Interestingly, corrosion pit was also found on compressive surface, which might attribute to this location creating enclosed environment causing Cl- to diffuse hardly. Then, pit grew under the occluded oxide crust composed of special crystalline corrosion products. When pit approached to critical size, crack initiated from it. The critical size of pit for crack initiation from pit was 35 μm on tensile surface and 95 μm on compressive surface. The sensitivity of crack initiation in tensile surface was higher than that in compressive surface. Then, cracking on compressive surface was controlled by slip dissolution mechanism, that is, dislocation outcrop generated through plastic deformation during manufacturing and absorbed Cl- in enclosed environment to accelerate metal dissolution and film rupture. Thereupon, the stress corrosion cracking on compressive surface was able to be maintained. The findings compared corrosion damage modes caused by the two kinds of stress and emphasized the nonignorable role of compressive stress on stress corrosion damage.

The effects of surfactants on plunging breakers

The effects of surfactants on a mechanically generated plunging breaker are studied experimentally in a laboratory wave tank. Waves are generated using a dispersively focused wave packet with a characteristic wavelength of $\lambda _0 = 1.18$ m. Experiments are performed with two sets of surfactant solutions. In the first set, increasing amounts of the soluble surfactant Triton X-100 are mixed into the tank water, while in the second set filtered tap water is left undisturbed in the tank for wait times ranging from 15 min to 21 h. Increasing Triton X-100 concentrations and longer wait times lead to surfactant-induced changes in the dynamic properties of the free surface in the tank. It is found that low surface concentrations of surfactants can dramatically change the wave breaking process by changing the shape of the jet and breaking up the entrained air cavity at the time of jet impact. Direct numerical simulations (DNS) of plunging breakers with constant surface tension are used to show that there is significant compression of the free surface near the plunging jet tip and dilatation elsewhere. To explore the effect of this compression/dilatation, the surface tension isotherm is measured in all experimental cases. The effects of surfactants on the plunging jet are shown to be primarily controlled by the surface tension gradient ( $\Delta \mathcal {E}$ ) while the ambient surface tension of the undisturbed wave tank ( $\sigma _0$ ) plays a secondary role.

Compression resistance and color evaluation in artisanal red bricks: Experimental study and numerical simulation

An experimental study is presented, simulating the firing process of artisanal red brick in a laboratory muffle. Under controlled heating conditions, the influence of both temperature and time on both the compressive strength and surface color of model bricks are evaluated. A production run and numerical simulations of laboratory brick heating are used to define the experimental conditions in the laboratory. A statistical model replicates the behavior of the compressive resistance at different temperatures, both in the muffle furnace and in production. Brick color has a more representative tone of a well-burned brick when created at the burning temperatures suggested in the literature.

A Comparative Evaluation of Compressive Resistance and Surface Hardness of Two Elastomeric Interocclusal Recording Materials: An In Vitro Study

A Comparative Evaluation of Compressive Resistance and Surface Hardness of Two Elastomeric Interocclusal Recording Materials: An In Vitro Study

Influence of Three-Dimensional Printing Parameters on Compressive Properties and Surface Smoothness of Polylactic Acid Specimens.

While the mechanical performance of fused filament fabrication (FFF) parts has been extensively studied in terms of the tensile and bending strength, limited research accounts for their compressive performance. This study investigates the effect of four process parameters (layer height, extrusion width, nozzle temperature, and printing speed) on the compressive properties and surface smoothness of FFF parts made of Polylactic Acid (PLA). The orthogonal Taguchi method was employed for designing the experiments. The surface roughness and compressive properties of the specimens were then measured and optimized using the analysis of variance (ANOVA). A microscopic analysis was also performed to identify the failure mechanism under static compression. The results indicated that the layer height had the most significant influence on all studied properties, followed by the print speed in the case of compressive modulus, hysteresis loss, and residual strain; extrusion width in the case of compressive strength and specific strength; and nozzle temperature in the case of toughness and failure strain. The optimal design for both high compressive properties and surface smoothness were determined as a 0.05 mm layer height, 0.65 mm extrusion width, 205 °C nozzle temperature, and 70 mm/s print speed. The main failure mechanism observed by SEM analysis was delamination between layers, occurring at highly stressed points near the stitch line of the PLA prints.

Effect of Porosity and Pore Shape on the Mechanical and Biological Properties of Additively Manufactured Bone Scaffolds.

This study investigates the effect of porosity and pore shape on the biological and mechanical behavior of additively manufactured scaffolds for bone tissue engineering (BTE). Polylactic acid scaffolds with varying porosity levels (15-78%) and pore shapes, including regular (rectangular pores), gyroid, and diamond (triply periodic minimal surfaces) structures, are fabricated by fused filament fabrication. Murine-derived macrophages and human bone marrow-derived mesenchymal stromal cells (hBMSCs) are seeded onto the scaffolds. The compressive behavior and surface morphology of the scaffolds are characterized. The results show that scaffolds with 15%, 30%, and 45% porosity display the highest rate of macrophage and hBMSC growth. Gyroid and diamond scaffolds exhibit a higher rate of macrophage proliferation, while diamond scaffolds exhibit a higher rate of hBMSC proliferation. Additionally, gyroid and diamond scaffolds exhibit better compressive behavior compared to regular scaffolds. Of particular note, diamond scaffolds have the highest compressive modulus and strength. Surface morphology characterization indicates that the surface roughness of diamond and gyroid scaffolds is greater than that of regular scaffolds at the same porosity level, which is beneficial for cell attachment and proliferation. This study provides valuable insights into porosity and pore shape selection for additively manufactured scaffolds in BTE.

Circular, zero waste formwork - Sustainable and reusable systems for complex concrete elements

The construction sector contributes significantly to global carbon emissions, leading to a new need and demand for sustainable and material-efficient construction technologies. Digital form-finding, simulation, and optimization methods are advancing, resulting in highly efficient, but often geometrically complex components. Concrete construction, which is currently dominant worldwide and crucial for sustainable material savings due to its large market volume, still faces challenges in implementing complex geometries. The significant requirements for formwork material and limitations in feasibility and cost at the current state of the art contribute to these challenges. This research presents a zero waste process using recyclable and reusable digitally fabricated formwork made from waste ingredients that can be immediately implemented in the construction industry. Residual sands (quartz and ceramics) were investigated as a basic moulding material in combination with biogenic binders (bentonite, eco-resin, sodium silicate, starch) for the production of stable formwork composites. The material compound were shaped into precise complex forms using 5-axis milling, and the removed material was recycled in a closed material cycle. Testing and characterization methods for evaluating mechanical properties such as compressive forces (20.1 N/mm2), surface roughness (Ra 9.1 μm), tolerances (0), and moulding processes indicate that the presented procedure conforms to common industry standards. Demonstrating feasibility, complex ultra-thin 1:1 concrete prototypes were designed and manufactured under industrial conditions using prefabricated formworks made of researched bio composite. The resulting high-resolution formwork surfaces and exposed concrete precast elements correspond to the highest fair-faced concrete class (SB04), with line roughness values of Ra 14.4 μm. The developed circulation concept allows reproducibility of different geometries and repeated concreting of formwork moulds. The formwork process is free from harmful additives, enabling recycling through grinding and reintegration into a closed material cycle. Sustainability has been continuously monitored and evaluated through a life cycle assessment. This system utilizes standard machines and offers an accessible and easily integrated approach for a holistic zero waste solution, suitable for efficient industrial applications.

On modal decomposition as surrogate for charge-conservative EHD modelling of Taylor Cone jets

The dynamics of the interface of a fluid jet subjected to an external electrostatic field forming a Taylor cone jet is investigated using a numerical approach. A charge-conservative electrohydrodynamic model is used. In this model, the reduced form of Maxwell’s equations for an electrostatic field, a transport equation for electric charges and the Navier–Stokes equations for a laminar flow are solved. The connection between the electric field and the hydrodynamic flow is established by the Maxwell stress tensor, which ensures the description of the electric surface forces. A fluid volume model based on surface compression provides an efficient and robust modulation of the overall behaviour of the electric drive of immiscible flows. Test cases from the literature López-Herrera et al. (2011); Roghair et al. (2015) help us to validate the numerical model. The order of accuracy of the spatial and temporal discretization of the electric field equations is computed through a quasi one-dimensional test case. The primary decay of a Taylor cone beam is then simulated with uniform droplet emission. This simulation is validated with experimental results from the literature Taylor (1969). To analyse the dynamics of the flow, it is proposed to use decomposition methods such as Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) using snapshots of the flow field. The dynamic structures formed by the velocity field and the dynamics of the electric charge determine the fundamental dynamics of the droplet emission. An analysis of the sensitivity of the modes to the sampling frequency is performed. The influence of different inlet velocities on the decomposition is analysed in the spatial and frequency domain. A reduced-order model (ROM) is interpolated from the base POD, and we demonstrate that it can be used to successfully construct the velocity and electric charge along the field. We anticipate numerous applications of this new type of ROM, such as for accelerating electrohydrodynamic calculations as surrogate models in digital twins.

Experimental Study on the Effect of the Freeze–Thaw Cycle in an Acidic Environment on the Mechanical Properties of Grout-Reinforced Rock Specimens

A new type of grouting material—FCM (fast cementing material)—is being used in coastal and offshore infrastructure projects, such as harbor and tunnel rehabilitation. In order to investigate how this material performs under different conditions, the compressive strength, failure mode, and surface microscopic changes of different fracture penetration degrees and different crack angles of grout-reinforced specimens formed by the FCM and sandstone were investigated in an acidic environment with pH = 1.1 and after freeze–thaw cycles of 5, 10, 20, and 30 times. In addition, through the preliminary determination of FCM grouting material fluidity and setting time, it was determined that the water-material ratio in this test is 0.3, and the sandstone used has good uniformity. The results show that the strength of the original rock can be matched or even exceeded by the solid grout of FCM and sandstone. Acidic environments and freeze–thaw cycles will erode the specimens, mainly on the surface of the specimens. The fracture penetration degree and crack angle determine the degree of strength reduction of the specimens. The compressive strength of the specimens decreases most rapidly within 10 freeze–thaw cycles. After soaking in acidic solution and a freeze–thaw cycle in an acidic environment, particle shedding occurs on the surface of the grout material and a “honeycomb” area appears on the surface of the sandstone. As the freeze–thaw cycle increases, the particle-shedding area and the honeycomb area increase continuously.

Ultrasonic pulsed waterjet peening of commercially-pure titanium

Commercially-pure titanium (CP-Ti) has proven indispensable in critical industries such as aerospace and automotive. To meet the ever-increasing demands of titanium applications, ultrasonic pulsed waterjet peening (UPWJ) has been evaluated for the first time on CP-Ti, as a novel method to optimise compressive surface residual stress. UPWJ offers the potential for an environmentally benign, non-contaminating peening process, paving the way for sustainable surface modification methods. UPWJ treatment involved directing a waterjet at a pressure of 69 MPa onto CP-Ti coupons, maintaining a stand-off distance of 25.4 mm and adjusting traverse speeds from 200 to 1000 mm/s. The effects of stand-off distance were also evaluated (varied from 25.4 to 44.4 mm), at a constant traverse speed of 1000 mm/s. Conventional shot peening was also applied on the same CP-Ti alloy as a baseline. The experimental results revealed relationships between the applied traverse speed and stand-off distance, and the measured surface roughness and residual stress. Furthermore, it was shown that UPWJ improves the surface mechanical behaviour, in terms of both the Rockwell hardness (HRB) and the scratch hardness. A higher stand-off distance and faster traverse speed contributed to increasing the induced compressive residual stress (to a maximum of −391 MPa), while keeping the surface roughness at moderate levels (i.e., Ra <3 μm). Comparing UPWJ with shot peening, this study highlights the potential of UPWJ for CP-Ti alloy surface modification, while removing the potential for surface contamination, which can be detrimental in many applications. Comparison of UWPJ used for peening Ti-6Al-4V (Grade 5) is also briefly discussed.

Mapping the structural properties of zinc scaffold fabricated via rapid tooling for bone tissue engineering applications

PurposeThe purpose of this study to investigate the organized porous network zinc (OPNZ) scaffolds. Their mechanical characteristics, surface roughness and fracture mechanism were assessed in relation to their structural properties. The prospects of fused deposition modeling (FDM) for printing metal scaffolds via rapid tooling have also been studied.Design/methodology/approachZn scaffolds with different pore and strut sizes were manufactured via the rapid tooling method. This method is a multistep process that begins with the 3D printing of a polymer template. Later, a paraffin template was obtained from the prepared polymer template. Finally, this paraffin template was used to fabricate the Zn scaffold using microwave sintering. The characterization of prepared Zn samples involved structural characterization, microstructural study, surface roughness testing and compression testing. Moreover, based on the Gibson–Ashby model analysis, the model equations’ constant values were evaluated, which can help in predicting the mechanical properties of Zn scaffolds.FindingsThe scanning electron microscopy study confirmed that the fabricated sample pores were open and interconnected. The X-ray diffraction analysis revealed that the Zn scaffold contained hexagonal closed-packed Zn peaks related to the a-Zn phase, validating that scaffolds were free from contamination and impurity. The range for ultimate compressive strength, compressive modulus and plateau stresses for Zn samples were found to be 6.75–39 MPa, 0.14–3.51 GPa and 1.85–12.6 MPa by adjusting their porosity, which are comparable with the cancellous bones. The average roughness value for the Zn scaffolds was found to be 1.86 µm.Originality/valueThis research work can widen the scope for extrusion-based FDM printers for fabricating biocompatible and biodegradable metal Zn scaffolds. This study also revealed the effects of scaffold structural properties like porosity, pore and strut size effect on their mechanical characteristics in view of tissue engineering applications.

Mechanical Properties of Metallic Materials Processed by Surface Severe Plastic Deformation

This paper gives an overview about some mechanical properties of materials processed by surface severe plastic deformation (SSPD) techniques. SSPD processed materials are classified in terms of their characteristics, and some main generated parameters that determine the output properties of materials are presented. The influences of SSPD on mechanical properties of materials are then reviewed. Furthermore, the roles played by some important parameters such as gradient microstructure, nanostructured layer, compressive residual stress (CRS) and surface integrity are highlighted by discussing their contributions to the mechanical properties of materials. Finally, some conclusions are drawn and possible prospects for future research are underlined.

Effect of process parameters in high shear granulation on characteristics of a novel co-processed mesoporous silica material

In this study, insights into the development and optimization of a co-processed excipient based on mesoporous silica are presented. The main advantage of such a material is that it is appropriate for direct tablet compression and has a sufficiently large specific surface area to be suitable for potential subsequent drug loading and formulation of (amorphous) solid dispersions. Our aim was to use a Design of Experiments approach to investigate which process parameters in high shear granulation affect the characteristics of such a co-processed material. The parameters included were the amount of binder (isomalt), the amount of water (granulation liquid), the water addition rate and the speed of the impeller. The responses evaluated and modelled were particle size and its distribution, specific surface area, bulk density, flowability, compressibility and compactibility. The models obtained showed good quality in terms of goodness of fit and predictive power. Active effects were identified for all responses, giving a thorough insight into factors affecting the material characteristics. Optimization experiments resulted in products with the desired characteristics (high specific surface area, large particle size, good flow and compression properties) and confirmed the validity of the generated models.

Strain Anisotropy Driven Spontaneous Formation of Nanoscrolls from 2D Janus Layers

Abstract2D Janus transition metal dichalcogenides (TMDs) have attracted attention due to their emergent properties arising from broken mirror symmetry and self‐driven polarization fields. While it has been proposed that their vdW superlattices hold the key to achieving superior properties in piezoelectricity and photovoltaic, available synthesis has ultimately limited their realization. Here, the first packed vdW nanoscrolls made from Janus TMDs through a simple one‐drop solution technique are reported. The results, including ab initio simulations, show that the Bohr radius difference between the top sulfur and the bottom selenium atoms within Janus (M = Mo, W) results in a permanent compressive surface strain that acts as a nanoscroll formation catalyst after small liquid interaction. Unlike classical 2D layers, the surface strain in Janus TMDs can be engineered from compressive to tensile by placing larger Bohr radius atoms on top (to yield inverted C scrolls. Detailed microscopy studies offer the first insights into their morphology and readily formed Moiré lattices. In contrast, spectroscopy and FETs studies establish their excitonic and device properties and highlight significant differences compared to 2D flat Janus TMDs. These results introduce the first polar Janus TMD nanoscrolls and introduce inherent strain‐driven scrolling dynamics as a catalyst to create superlattices.

6-month evaluation of concrete aging factor using chloride migration test: Effects of binder type and w/b ratio

Service life modeling is a relevant tool in the design of durable concrete structures. Among the service life prediction models, many introduce the so-called concrete aging factor, which aims to express the reduction of concrete diffusivity over time. This paper presents an experimental assessment of the concrete aging factor up to the age of 6 months based on the chloride migration coefficient. Several concretes produced with different binder types, mineral additions, and water/binder ratios were evaluated. Concrete compressive strength and surface electrical resistivity are also addressed. The results indicate a strong influence of the type of binder and the use of mineral additions on the aging factor of the concrete – especially in concretes with water/binder ratio = 0.45. The inclusion of the aging factor in service life prediction models and the extrapolation of data obtained at the first ages of concrete for long-term analysis are discussed.

Micro-mechanism on strength development and failure mode of cemented ultra-fine tailing backfill: Influence of binder

As cemented ultra-fine tailings filling method gains popularity, the demands for more economical and environment friendly binders rise. In order to better understand the influence of different binders on the mechanical properties of cemented ultra-fine tailings backfills (CUTBs), the CUTBs with solid materials of 72% for 3, 7, 14, 21 and 28d respectively were made by the water-quenched slag binder (WSB) and ordinary Portland cement (OPC). The microstructure characteristics and macro-mechanical properties of WSB-CUTB and OPC-CUTB at different ages were compared by uniaxial compressive strength (UCS), thermo-gravimetry (TG), X-ray diffraction (XRD) and surface electron microscope (SEM) tests. The results show that the strength development process of CUTBs with different binders has obvious phased characteristics, which can be divided into the initial germination (IG) stage, rapid growth (RG) stage and slow growth (SG) stage: the UCS of WSB-CUTB increases quicker than UCS of OPC-CUTB at the IG and RG stages, while the UCS of OPC-CUTB increases faster than UCS of WSB-CUTB at the SG stage. The micro-mechanism on strength development of CUTBs with different binders was revealed by the evolutional characteristics in the amounts and shapes of hydration products: the amount and shape of AFt are the primary factors which impact the strength development at the IG and RG stages, while the amount and shape of C-S-H are the primary factors which impact the strength development at the SG stage. As the age increases, WSB-CUTB transitions from brittle failure to brittle-ductile failure, while OPC-CUTB transitions from ductile failure to brittle-ductile failure. The micro-mechanism on the failure modes of CUTBs with different binders was revealed by the different characteristics in the skeleton composed of hydration products: the CUTBs with AFt-dominated skeleton will transition from brittle failure to brittle-ductile failure, while the CUTBs with C-S-H-dominated skeleton will transition from ductile failure to brittle-ductile failure. The research results provided theoretical guidance for applying CUTBs using WS as a binder.

A techno-economic approach for magnetising roasting of iron ore composite pellet using conventional and hybrid microwave furnace

The present study aims to enhance the iron ore fines through reduction roasting using a muffle and hybrid microwave furnace. The Taguchi statistical design was used to optimise the process variables such as temperature, time, and reductant concentration. The reduction roasting was followed by multi-pass low-mid intensity magnetic separation to treat the low-grade iron ore fines (Fe 44.53%, 40.13% silica). The results showed that the conventional reduction roasting at optimum conditions (800 °C, 60 min, 7% coal) produced a concentrate with 52.6% Fe grade and 77.3% recovery. The microwave roasting produced a concentrate with 53.06% Fe grade and 75.7% recovery at 750 °C, 2 min, and 7% coal as the reductant. The effect of both heating methods on compressive strength (CCS) and surface morphology was also studied. The results indicated that microwave heating resulted in a finer and more porous structure that improved the reducibility and ease of grinding. The techno-economic comparison showed that microwave reduction reduced the processing time by 85% and energy consumption by 73%. The study concludes that microwave heating followed by multi-pass magnetic separation can significantly improve the economic viability of exploiting lean iron ore fines.