Decrease In Compressive Stress Research Articles

Seismic analysis of asphalt concrete core rockfill dams considering the bimodulus effect

In China, with the extensive development of pumped storage power stations, asphalt concrete core rockfill dams have become the preferred dam type because of their good deformation adaptability and impermeability. In seismic-prone western regions of China, the seismic safety of asphalt concrete cores is particularly important. However, asphalt concrete materials used in hydraulic engineering exhibit significant differences in their tensile and compressive moduli under low-temperature conditions, which has not been considered in existing constitutive models. In this study, a dynamic constitutive model considering the bimodulus effect of asphalt concrete was developed on the basis of dynamic tension and compression tests. Using this model, the influence of the bimodulus characteristics on the dynamic response of the core was investigated. The results indicate that a bimodulus constitutive model can effectively simulate the stress‒strain relationship of asphalt concrete materials at low temperatures. Compared with the bimodulus model, the use of the monomodulus model for calculations results in a significant decrease in compressive stress and a substantial increase in tensile stress of the core. Specifically, using the tensile and compressive monomodulus models led to maximum reductions in tensile stress of 42.9 % and an increase by 336.8 %, respectively. Neglecting the bimodulus effect may lead to misjudgment of the damage area, so the bimodulus effect on the seismic safety of dam cores should not be ignored.

Effects of laser shock peening on silicon nitride ceramic with varying sintering additive ratios

Silicon nitride ceramic (Si3N4) for industrial applications is conventionally manufactured with sintering additives, and the properties of Si3N4 change significantly based on the contents of these additives. In this study, we investigate the effects of laser shock peening (LSP) on Si3N4 sintered with varying ratios of sintering additives.The Si3N4 samples were sintered with a mixture of Y2O3, MgO, and SiO2 sintering additives at 5, 7, 9, and 11 wt%. A Nd:YAG laser (wavelength = 532 nm, maximum pulse energy = 1.4 J, repetition rate = 10 Hz, pulse duration = 8 ns, beam diameter = 11 mm, top-hat profile) was used to irradiate the Si3N4 samples. The samples were coated with a protective layer (100 μm thick aluminum foil) and a water layer to confine plasma. LSP of Si3N4 with 5% sintering additives resulted in a slight change in surface hardness but a 77% decrease in surface compressive residual stress. In contrast, LSP of Si3N4 with 11% sintering additives led to a simultaneous increase in surface hardness (7.3%) and surface compressive residual stress (67%), indicating a significant difference in the effectiveness of LSP depending on the ratio of sintering additives. Additionally, the surface of Si3N4 with 11% sintering additives showed evidence of grain refinement after LSP. It was demonstrated that the bending strength of Si3N4 with 11% sintering additives increased by 15.2%, and the depth of the fracture origin was significantly deepened.

Effect of oxygen doping on cutting performance of CVD diamond coated milling cutters in zirconia ceramics machining

Diamond thin films were deposited on WC-Co tools using the hot-filament chemical vapor deposition (HFCVD) technique at varying pressures and oxygen doping levels. As the oxygen doping content increased, the purity of the diamond phase improved, and the density of the <111> crystal plane on the film's surface increased. The growth rate of diamond films initially increased and then decreased under low pressure, with a corresponding decrease in residual compressive stress. Conversely, at high pressure, increased oxygen doping enhanced the diamond phase purity and growth rate while reducing residual compressive stress. Cutting experiments on pre-sintered zirconia ceramics for milling linear slots and engraving dentures demonstrated that diamond-coated milling cutters exhibited superior cutting performance under consistent oxygen and carbon source concentrations and stable air pressure conditions. The oxygen-doped diamond-coated milling cutter grown at a pressure of 1 KPa exhibited the longest service life, attributed to its reduced surface roughness, lower cutting force, and increased density of the <111> crystal plane orientation. This cutter could machine up to 1300 crowns, making it approximately 80% more durable than non‑oxygen-doped diamond-coated milling cutters and about 20 times more durable than uncoated ones.

Experimental Evaluation of Mechanical Properties, Micro Structure and Post-Fire Strength of Fiber Reinforced Geopolymer Concrete

Geopolymer mixtures offer an enhanced alternative to implement an eco-friendly solution in construction industry. These mixtures exhibit similar or better mechanical and structural properties in comprising of cement and can use recycling and by-product materials. Against this background, an eco-friendly advantageous were achieved from the engineers and researchers by using waste materials to replace cement and attention to reduce CO2 emission during its procedure. This study attempted to evaluate compressive and tensile strength, micro structure and post-fire characteristic of the geopolymer mixtures. For this aim, the geopolymer mixtures were exposed to elevated temperature between 200, 500 and 800 0C. Then, the post-fire and mechanical behaviour were investigated. The proposed research supported the slight decrease in the GPC's compressive stress by fibres, and the 1.25% PP fibres displayed the least performance, indicating nearly 13% decrease than the unreinforced mixtures. As exhibited by the post-fire behaviour of mixtures, the GPC's compressive strength increased first for all mixes but in the range of 400 - 800°C it decreased at a higher rate because of the geopolymer matrix-related dehydration. Besides, fiber melting under high temperatures and the thermal reaction procedure related to free water evaporation reduce the mechanical properties under temperatures ranging from 400°C to 800°C. DOI: https://doi.org/10.52783/pst.349

Experimental investigation of tungsten–nickel–iron alloy, W95Ni3.5Fe1.5, compared to copper monolithic bullets

Introduction:The demand for improved small arms ammunition has led to exploring advanced materials and manufacturing techniques. This research investigates the machining characteristics of CM and WNF alloy bullets, aiming to enhance ballistic performance and durability.Methods:Bullet profile-making trials were conducted to evaluate the impact of machining parameters such as cutting speed and feed. The study also considered variables including surface roughness, cutting temperature, and hardness, alongside a detailed morphological analysis, The evaluation utilized an orthogonal array and MCDM approach, incorporating the TOPSIS method for decision-making processes.Results:The findings reveal that WNF alloy bullets exhibit 3.01% to 27.95% lower machining temperatures, 24.88%-61.85% reduced surface roughness, and 19.45%-34% higher microhardness compared to CM bullets. Moreover, CM bullets demonstrated higher machining temperatures, resulting in 47.53% increased tool flank wear. WNF bullets showed a 24.89% reduction in crater wear and a 38.23% decrease in compressive residual stress in bullet profiles, indicating superior machining performance.Discussion:The superior machining performance of WNF alloy bullets suggests their potential to improve the ballistic performance and durability of small arms ammunition. The reduced tool wear and favorable machining parameters highlight WNF alloy's advantages for military and defense applications. A ballistic impact analysis using a finite element method (FEM) model in Abaqus software further supports the potential of WNF alloy bullets, providing a solid foundation for future advancements in bullet manufacturing technologies.

Optimization of transparent conductive properties of magnetron sputtered Sb-doped SnO2 films by RF power: Towards application in polymer-dispersed liquid crystal (PDLC) films

Sb-doped SnO2 (ATO) films were prepared with different RF powers (PRF) under two O2 flow rates (FO2) by magnetron sputtering, and then subjected to rapid thermal annealing (RTA) treatment. The effects of PRF, FO2, and RTA on the crystallinity, stress, surface morphology, conductive properties, transmittance in visible-light range (TVis), and energy gap (Eg) of the films were investigated. As the PRF increases, the film crystallinity improves or first improves and then slightly degrades, and the compressive stress decreases. With increasing PRF, the surface changes from textured to granular morphology and from granular to honeycomb-like morphology under two FO2, respectively. Meanwhile, the conductive properties first enhance and then degrade, and the TVis and Eg tend to decrease, especially at higher PRF. Basically, the films prepared with higher FO2 have lower compressive stress, inferior conductive properties, and larger TVis and Eg compared with the films prepared with lower FO2. After RTA, the film crystallinity obviously improves, the compressive stress transforms into tensile stress, and the surface morphology has not undergone significant changes. Meanwhile, the conductive properties significantly enhance and Eg obviously increases. The TVis of the films prepared with lower FO2 can be increased by RTA. The influence mechanisms of the above factors on the structure and optoelectronic properties of the ATO films were explored, and ultimately, the ATO films have the TVis of 76.35–80.86%, sheet resistance of 51.7–91.9 Ω/sq., and quality factor of 1.03–1.67 × 10−3 Ω−1 within the optimized PRF range. Polymer-dispersed liquid crystal (PDLC) films were fabricated using optimized performance ATO films as electrodes, and their on-state transmittance, off-state transmittance, threshold electric field, and saturation electric field were 2.08–4.61%, 61.69–68.56%, 0.656–0.796 V/μm, and 1.68–2.108 V/μm, respectively. The current results indicate the potential application of ATO films in PDLC films as electrode.

Seismic performance improvement of liquid storage tank based on base-isolation and pendulum tuned mass damper

It is necessary to ensure the safety of liquid storage tanks under earthquakes, but the damage probability of the non-damping liquid storage tanks is higher under earthquakes. Based on the damping principle of tuned mass damper (TMD) and the characteristics of the liquid storage tank, a new pendulum TMD (PTMD) system is proposed. Considering the material nonlinearity, the fluid–structure interaction and liquid sloshing characteristics, the three-dimensional numerical calculation models of the non-damping, PTMD, base-isolation (BI) and BI-PTMD liquid storage tanks are established, respectively. The seismic responses of different types of liquid storage tanks under the action of near-field pulse-like earthquakes are investigated, the damping performance of the hybrid control system with the isolation and the PTMD is analyzed, and the influence laws of the mass ratio of PTMD-structure and base-isolation period on the dynamic responses of the liquid storage tanks are discussed. The results show that the BI-PTMD hybrid control system has a significant damping effect on the seismic responses of the liquid storage tank. The damping rate of the base shear is the largest, reaching 86.0%, and the control rate of the PTMD on the displacement of the isolation layer is about 20.0%. The hoop stress, effective stress, liquid pressure and displacement of isolation layer decrease with the increase of the mass ratio of PTMD to structure. With the increase of base-isolation period, the hoop stress, axial compressive stress, effective stress and liquid pressure decrease, and the control effect of PTMD on the liquid storage tank is weakened.

Performance Of Pervious Concrete as A Replacement for Road Curb

Pervious concrete is a well-known type of concrete characterized by its high porosity and permeability. It finds extensive use in road infrastructure, particularly in pavement construction, and offers cost-saving benefits due to the absence of fine aggregates in its mixture. While road curbs are still commonly built today, the utilization of pervious concrete as a substitute for curbs is rarely observed. Therefore, this study focuses on evaluating the compressive strength, flexural strength, and suitability of pervious concrete as a curb replacement. In this investigation, different water cement ratios (0.30, 0.33, 0.35, 0.38, and 0.40) were employed during the mixing of pervious concrete to determine the most optimal ratio and achieve the highest compressive and flexural strength for the road curb. To obtain the results, compressive and flexural tests were conducted on ten curb samples after a curing period of 28 days. The study aimed to examine the diverse effects of the various water cement ratios. The findings indicate a decrease in compressive stress as the water cement ratio increased. Furthermore, the compressive strength of the concrete mix was significantly stronger at a water cement ratio of 0.30 but exhibited a decline with higher ratios. Similar results were obtained in the flexural test, where a water cement ratio of 0.30 recorded the highest value of flexural strength. However, a water cement ratio of 0.40 yielded the second-highest flexural strength. These results emphasize that a lower water cement ratio leads to higher concrete strength. To further enhance the strength of the concrete, several recommendations are proposed, including the use of coating reinforcement bars, adjustment of coarse aggregate size, and the addition of admixtures to the pervious concrete mixture.

Effect of dislocation and residual stress on etching performance of 12 μm thick rolled copper foil during pre-stretching

With the rapid development of new electronic information industry in 5G era, the development of various electronic components towards high speed and multi-functionality, and higher requirements have been put forward on the precision of circuit boards, the quality and rate of signal transmission. The 12 μm thick rolled copper foil is the thinnest rolled copper foil that can be stably produced, which is essential for the manufacture of high-end Flexible Printed Circuit (FPC) boards. The different microstructure and stress states of 12 μm thick rolled copper foil was obtained through different degrees of pre-stretching. And then the effect of dislocation and residual stress on the etching performance of copper foil was systematically investigated. The results show that the etching rate of copper foil increases and then decreases with the increasing of pre-stretching strain. And the etching rate of copper foil increases rapidly when the pre-stretching strain increases from 0.67% to 0.83%. For the dislocation, the rolled copper foil has higher dislocation density, and the dislocation density gradually increases with the increasing of pre-stretching strain. For the residual stress, the rolled copper foil has higher residual compressive stress. The residual compressive stress decreases and then turns into residual tensile stress with the increasing of pre-stretching strain. The residual compressive stress and dislocation reduce the etching rate of copper foil, and the residual tensile stress increases the etching rate of copper foil within a certain range. The four stages of etching rate variation of copper foil during pre-stretching were clarified, and the calculating model of etching rate was constructed when the dislocation density or residual stress acts as a single factor or dual factors.

Effect of gas pressure on microstructure and mechanical properties of TC11 titanium alloy during supersonic fine particle bombardment

The surface nanocrystallization of a Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) titanium alloy with a lamellar microstructure was carried out by supersonic fine particle bombardment (SFPB). The effect of SFPB gas pressure on its surface integrity, microstructural evolution and mechanical properties was systematically investigated. The results showed that gradient nanostructures on the surface of the TC11 alloy were successfully created after SFPB with different gas pressures. The grain size of the surface’s lamellar microstructure was completely refined to the nanometer scale. And the grain size of nanocrystals decreased with the increase of gas pressure. Meanwhile, the subsurface retained initial lamellar microstructure morphology. Surface roughness was minimized after SFPB with a gas pressure of 1.0 MPa, while microcrack formed at a higher gas pressure of 1.5 MPa, resulting in a decrease of compressive residual stress. With the increase of SFPB gas pressure, the surface microhardness and the depth of hardened layer gradually increased, and yield strength and tensile strength was improved. Nevertheless, the elongation was not greatly changed. The fracture morphology changed from typical ductile fracture to quasi-cleavage and ductile mixed fracture.

Study on the fundamental factors of the property evolution of a 300 mm polycrystalline trap-rich layer

The geometry and resistivity of the trap-rich layer are key parameters for 300 mm trap-rich silicon-on-insulator (TR-SOI) wafers. In this paper, the evolution of the warpage and resistivity of poly-Si layers grown by atmospheric chemical vapor deposition with deposition temperature has been studied. The ability to quantify the surface grain size of undoped poly-Si was evaluated using scanning electron microscopy, electron backscattering diffraction, and transmission Kikuchi diffraction (TKD). With a resolution scale of several nanometers, the fine grains on the surface of poly-Si are accurately identified by TKD. It is confirmed that the decrease in compressive stress with deposition temperature is caused by the lower ratio of (110) grain orientation and the reduction of fine grains on the surface. However, when stress is released, the random grain boundaries (GBs) of poly-Si change into coincidence site lattice low-Σ GBs with low recombination activity, which greatly lowers the film bulk resistivity and reduces its capacity to trap charges. Thus, a process window for the manufacturing of 300 mm TR-SOI wafers is created by balancing the degradation of resistivity in the process of using deposition temperature to seek improvements in poly-Si warpage.

Modulus matching strategy of ultra-soft electrically conductive silicone composites for high performance electromagnetic interference shielding

Electrically conductive silicone composites have made significant advancements in the field of electromagnetic interference (EMI) shielding due to their excellent conductivity, elasticity, sealability and environmental reliability. Notably, chips and other miniature electronic components with limited pressure-bearing capacity often require composites with both low compressive stress and high EMI shielding performance. Unfortunately, conventional conductive silicone composites often exhibit high compressive stress as a result of the high modulus and high loading contents of fillers, which prevents them from fitting perfectly with the package cavity under low package stress conditions, resulting in inadequate EMI shielding. Herein, the elastic modulus of the silver@polydimethylsiloxane (Ag@PDMS) conductive filler can be adjusted by controlling the crosslinking ratio, which enables the creation-of-Ag@PDMS/Silicone-(APS)-conductive-composites-with-remarkable compressibility, EMI shielding and sealing capabilities. The-APS-composites exhibit a compressive stress of only 0.3 MPa under 50 % compressive strain, which is essential for the packaging-of-precision electronic components. The APS composites show a significant decrease in compressive stress (54 %) and elastic modulus (80 %) under 50 % compressive strain, in comparison to conventional polymer composites with hard fillers. Meanwhile, the APS composites exhibit a-satisfactory-EMI-shielding-effectiveness-(SE)-of-71-dB and demonstrate excellent electromagnetic sealing capabilities in practical electronics. This study provides an effective approach for developing and constructing high-performance ultra-soft composites for precision electronic components packaging.

An experimental and computational investigation of embedded wrinkle’s impacts on the compressive responses of thick unidirectional glass fiber-reinforced composites

In thick unidirectional glass fiber-reinforced composites, the out-of-plane embedded wrinkle flaws have a major impact on compressive failure, which should be taken into account and assessed during the design, manufacturing, and inspection phases. The thick unidirectional coupons with embedded wrinkles of various severities were manufactured and tested. The deformation of the wrinkle region was captured by the Digital Image Correlation (DIC). As the wrinkle angle increased, the compressive failure stress decreases and the modulus does not change significantly, while the wrinkle amplitude has a negative effect on both the compressive failure stress and elastic modulus. The linear texture image regression approach is used to account for the path of fibers. The high-fidelity three-dimensional finite element (FE) models considering the real paths of the fibers are established. To reveal the interplay and impact of wrinkle severity parameters on the compressive failure behavior of composites, the progressive damage analyses and cohesive elements are also incorporated. Compared with the experiments, the FE studies accurately identify the dominant failure modes and failure stress values for various wrinkle severity parameters.

Application of laser-shock-wave processing in additive technologies

The patterns of occurrence of residual stresses with the simultaneous use of additive technologies and lasershock-wave processing (LSWP) are studied. The mechanisms of thermal decrease and increase, mechanical decrease and increase of compressive residual stresses during layer-by-layer build-up of the material and LSWP are described. Keywords: additive technologies, laser-shock-wave processing, hybrid additive technology, finite element method, compressive residual stresses. sakhvadze@mail.ru

Warpage Reduction and Thermal Stress Study of Dicing Process in Wafer-to-Wafer Bonding Fabrication

We successfully study the warpage after wafer-to-wafer (W2W) bonding by the experiments and the full wafer model simulation. Furthermore, the effect of the dicing process on the warpage reduction and the thermal stress of bonded wafer are investigated by varying the dicing pitch from a one pitch as chip size to a quarter pitch. When the dicing pitch decreases to a quarter pitch, the bonded wafer warpage is observed to decrease by 27.8%. A full wafer model is established with the representative volume element (RVE) method in simulation and validated by good agreement with the measured wafer warpage data. The radial stress distribution of bonded wafer indicates tensile stress for the dynamic random access memory (DRAM) layers and compressive stress for the DRAM/Si substrate interface of top and bottom wafers due to the shrinkage of the DRAM layers under the temperature decrease from its high fabrication temperature to the room temperature. The radial stress distribution after the dicing process with different pitches indicates a similar stress level after one-pitch dicing and half-pitch dicing. When the dicing pitch decreases to a quarter value, the compressive stress decreases, correspondingly resulting in a warpage reduction. The stress released by interrupting the continuity of the wafer with a small dicing pitch is revealed to be the origin of wafer warpage reduction. This study provides a guideline of dicing street pitch for warpage reduction and is useful for optimizing the device layout design.

The intrinsic mechanical properties of NbTaTiZr and the influence of alloying elements Mo and W: A first-principles study

The intrinsic mechanical properties of NbTaTiZr and NbTaTiZrX (X Mo, W) are studied by using a first-principles calculation in combination with special quasi-random structure. For NbTaTiZr RHEA, the ideal tensile strength (ITS) and compressive strength (ICS) along [001] direction is respectively calculated to be 5.64 GPa and −18.4Gpa at the strain 11% and −20%. For shear loading along (211)[111] slip system, the ideal shear strength (ISS) is 3.03 GPa as the strain is about 20%. With addition of Mo into NbTaTiZr, the ITS, ICS and ISS respectively increase up to 9.7, −19.3 and 4.73 GPa, and the addition of W enhances the ITS, ICS and ISS up to 10.5, −21.1 and 5.12 GPa, respectively. Hence addition of Mo or W can significantly improve the ideal strength, especially stronger impact of W element. The calculated elastic moduli E [001] and G [111] are in reasonable agreement with the initial slope of the stress-strain relationship. The derived dimensionless ITS and ISS from first-principle calculations is underestimated the ideal strength in comparison with the prediction by the universal empirical model. Then the microcosmic mechanism is further studied by examination of the detailed bond length variation of three HEAs during the corresponding deformation. Near the critical strain under of tension and shear, the slower descend of stress originates from the gradual breakage of atomic bonds, while the compressive stress decreases rapidly owing to all bond fracturing almost simultaneously. Finally, the ideal strength of three HEAs is further analyzed from electronic structure. • The ideal strength is studied using ab initio calculations based on special quasi-random model. • The ideal strength and critical strain show NbTaTiZr has good strength and ductility. • The dimensionless ideal strength is overestimated in the empirical model. • The slow descend of tensile/shear stress results from the gradual breakage of atomic bonds. • The rapid decrease of compressive stress is due to the almost simultaneous fracture of all bonds.

Spacing and strain during multiphase boudinage in 3D

Most models of brittle boudinage predict a dependency of fracture spacing on thickness of the boudinaged layer. This basic relationship can be distorted in the case of multiphase boudinage, where structural inheritance, possibly combined with time evolution of rheology affects boudin geometries, but is not recognized in 2D outcrops. Here we present analyses from a metre-scale, serially sectioned sample of marble from Naxos, Greece, containing a layer of amphibolite, which is known to have experienced two phases of ductile drawn boudinage followed by five generations of brittle boudinage. We show that brittle boudinage depends on the ratio of grain size and layer thickness of the amphibolite. In very thin layers (few grains across), strain is diffuse throughout the entire layer, leading to macroscopically homogeneous stretching. Strain localisation starts when layer thickness exceeds 5 grains: narrow tensile necks and shear zones (35–45° dip) develop where the layer is < 10–20 grains thick. Thicker layers (<30–40 grains) show extensional (mode 1) fractures while shear fractures form in even thicker layers. The absence of shear fractures in thinner layers may be explained by a geometry-related compressive stress decrease in the pinches. This results in localised shear evolving only in thicker layers. Complete delocalisation where layer thickness approaches the grain scale is expected as the typical shear bandwidth in granular media (10–20 grains) exceeds layer thickness. Successive fracture reactivation causes geometrical complexity in the form of splays and branches, and in addition the thickness-dependence of strain localisation governs fracture distribution in the layer. A second, temporal trend is recorded in the progressive embrittlement of the rocks as they cooled during exhumation, evidenced by increasing fracture density and a switch from shear to extensional fracturing. In the final stages, the marble was brittle enough to allow fracture propagation from the amphibolite across the material interface into the marble and, finally, the formation of brittle fractures affecting both the amphibolite and marble.

Tribocorrosion and tribological behavior of Ti-DLC coatings deposited by filtered cathodic vacuum arc

In order to improve the tribological and tribocorrosion performance of Ti-DLC films, a series of Ti-DLC films were prepared by filtered cathodic vacuum arc technique by controlling C2H2 flow rate. The microstructure, mechanical properties, tribological and tribocorrosion performance of Ti-DLC films with different C2H2 flow rates were investigated. As the C2H2 flow rate increased from 10 to 140 sccm, the columnar cross-sectional structure of the Ti-DLC films transformed to dense and uniform structure. The increase in C2H2 flow rate also resulted in an initial increase followed by a decrease in hardness and compressive stress. The results showed that the Ti-DLC films on substrate can significantly improve its tribology, anti-corrosion and anti-tribocorrosion properties. Under dry friction condition, the film prepared at 20 sccm with hardness of 49.1 GPa showed low wear rate at a reciprocating frequency of 1 Hz under a load of 2 N (2 N/1 Hz), however, the film was worn through due to the high compression stress at 10 N/5 Hz. The film at 140 sccm showed great tribology performance with the lowest coefficient of friction of 0.017 and the lowest wear rate of 5.91 × 10−8 mm3/N·m at 10 N/5 Hz, which was attributed mainly to the formation of sp2-carbon rich transfer layers on the counterpart. The tribocorrosion properties test demonstrated that the coating prepared at 140 sccm exhibited the best tribocorrosion resistance with the lowest coefficient of friction of 0.055, the lowest wear rate of 3.56 × 10−7 mm3/N·m and high stable value of OCP of 0.116 V under the synergistic action of corrosion and friction.

Surface defects, stress evolution, and laser damage enhancement mechanism of fused silica under oxygen-enriched condition

Oxygen ions (O+) were implanted into fused silica at a fixed fluence of 1 × 1017 ions/cm2 with different ion energies ranging from 10 keV to 60 keV. The surface roughness, optical properties, mechanical properties and laser damage performance of fused silica were investigated to understand the effect of oxygen ion implantation on laser damage resistance of fused silica. The ion implantation accompanied with sputtering effect can passivate the sub-/surface defects to reduce the surface roughness and improve the surface quality slightly. The implanted oxygen ions can combine with the structural defects (ODCs and E′ centers) to reduce the defect densities and compensate the loss of oxygen in fused silica surface under laser irradiation. Furthermore, oxygen ion implantation can reduce the Si–O–Si bond angle and densify the surface structure, thus introducing compressive stress in the surface to strengthen the surface of fused silica. Therefore, the laser induced damage threshold of fused silica increases and the damage growth coefficient decreases when ion energy up to 30 keV. However, at higher ion energy, the sputtering effect is weakened and implantation becomes dominant, which leads to the surface roughness increase slightly. In addition, excessive energy aggravates the breaking of Si–O bonds. At the same time, the density of structural defects increases and the compressive stress decreases. These will degrade the laser laser-damage resistance of fused silica. The results indicate that oxygen ion implantation with appropriate ion energy is helpful to improve the damage resistance capability of fused silica components.

Compressive Behaviour of 3D-Printed PETG Composites

It is known that 3D-printed PETG composites reinforced with carbon or Kevlar fibres are materials that can be suitable for specific applications in the aeronautical and/or automotive sector. However, for this purpose, it is necessary to understand their mechanical behaviour, which is not yet fully understood in terms of compression. Therefore, this study intends to increase the knowledge in this domain, especially in terms of static behaviour, as well as with regard to creep and stress relaxation due to the inherent viscoelasticity of the matrix. In this context, static, stress relaxation and creep tests were carried out, in compressive mode, using neat PETG and PETG composites reinforced with carbon and Kevlar fibres. From the static tests, it was found that the yield compressive strength decreased in both composites compared to the neat polymer. Values around 9.9% and 68.7% lower were found, respectively, when carbon and Kevlar fibres were added to the PETG. Similar behaviour was observed for compressive displacement, where a reduction of 20.4% and 46.3% was found, respectively. On the other hand, the compressive modulus increased by 12.4% when carbon fibres were added to the PETG matrix and decreased by 39.6% for Kevlar fibres. Finally, the stress relaxation behaviour revealed a decrease in compressive stresses over time for neat PETG, while the creep response promoted greater compressive displacement. In both situations, the response was very dependent on the displacement/stress level used at the beginning of the test. However, when the fibres were added to the polymer, higher stress relaxations and compressive displacements were observed.