Strength and Fracture Mechanism of an Ultrafine-Grained Austenitic Steel for Medical Applications

In this paper, we study the corrosion-resistant austenitic steel Fe-0.02C-18Cr-8Ni for medical applications. The microstructure and mechanical properties (tensile mechanical properties, torsional strength, impact toughness, and static and cyclic crack resistance) under different types of loading of the steel are investigated. The results are compared for the two states of the steel: the initial (coarse-grained) state and the ultrafine-grained state produced by severe plastic deformation processing via equal-channel angular pressing. It is demonstrated that the ultrafine-grained steel 0.08C-18Cr-9Ni has essentially better properties and is very promising for the manufacture of medical products for various applications that experience various static and cyclic loads during operation.     

Simulated and Experimental Investigation of Mechanical Properties for Improving Isotropic Fracture Strength of 3D-Printed Capsules

Three-dimensional (3D) printer-based self-healing capsules, embedded in cement composites, were proposed to heal cracks, as they allow for various structural designs of capsules, repeatable fabrication, and strength analysis. Out of many 3D printing methods, such as fusion deposition modeling (FDM), powder layer fusion, and PolyJet printing, FDM was used to design, analyze, and produce new self-healing capsules, which are widely used due to their high-speed, low-cost, and precise manufacturing. However, the PLA extruded in the FDM had low adhesion energy between stacked layers, which caused a degradation of the performance of the self-healing capsule, because it had different strengths depending on the angle between the stacked layers and the applied load within the concrete structure. Therefore, in this paper, specimens were produced, in accordance with ASTM specifications, using the FDM PLA method, and mechanical properties were obtained through tensile, shear, and compression tests. Additionally, the isotropic fracture characteristics of the four types of capsules were analyzed through finite element method analysis. Subsequently, the 3D-printed capsules were produced, and the fracture strength was analyzed in the x, y and z directions of the applied load through a compression test. As a result, the newly proposed capsule design was verified to have an isotropic fracture strength value of 1400% in all directions compared to conventional spherical thin film capsules     

Interface Joint Strength between SS316L Wrought Substrate and Powder Bed Fusion Built Parts

Metal powder bed fusion (PBF) additive manufacturing (AM) builds metal parts layer by layer upon a substrate material. The strength of this interface between the substrate and the printed material is important to characterize, especially in applications where the substrate is retained and included in the finished part. Ensuring that this interface between the original and the printed material has adequate material properties enables the use of this PBF AM process to repair existing structures and create new parts using both AM and conventional manufacturing. This paper studies the tensile and torsional shear strengths of wrought and PBF-built SS316L specimens and compares them to specimens that are composed of half wrought material and half PBF material. These specimens were created by building new material via PBF onto existing wrought SS316L blocks, then cutting the specimens to include both materials. The specimens are also examined using optical microscopy and electron backscatter diffraction (EBSD). The PBF specimens consistently exhibited higher strength and lower ductility than the wrought specimens. The hybrid PBF/wrought specimens performed similarly to the wrought material. In none of the specimens did any failure appear to occur at or near the interface between the wrought substrate and the PBF material. In addition, most of the deformation in the PBF/wrought specimens appeared to be limited to the wrought portion of the specimens. These results are consistent with optical microscopy and EBSD showing smaller grain size in the PBF material, which correlates to increased strength in SS316L due to the Hall–Petch relationship. With the strength at the interface meeting or exceeding the strength of the original wrought material, this process shows great promise as a method for adding additional features or repairing existing structures using metal PBF AM.     

Prediction of the Interface Shear Strength between Ultra-High-Performance Concrete and Normal Concrete Using Artificial Neural Networks

The bond strength between ultra-high-performance concrete (UHPC) and normal-strength concrete (NC) plays an important role in governing the composite specimens’ overall behaviors. Unfortunately, there are still no widely accepted formulas targeting UHPC–NC interfacial strength, either in their specifications or in research papers. To this end, this study constructs an experimental database, consisting of 563 and 338 specimens for splitting and slant shear tests, respectively. Moreover, an additional 35 specimens for “improved” slant shear tests were performed, which could circumvent concrete crushing and trigger interfacial debonding. Additionally, for the first time in our tests, the effect of casting sequence on UHPC–NC bond strength was identified. Based on the database, an artificial neural network (ANN) model is proposed with the following inputs: namely, the normal stress perpendicular to the interface, the interface roughness, and the compressive strengths of the UHPC and NC materials. Based on the ANN analyses, the explicit expression of UHPC–NC bond strength is proposed, which significantly lowers the prediction error. To be fully compatible with the specifications, the conventional shear-friction formula is modified. By splitting the total force into adhesion and friction forces, the modified formula additionally takes the casting sequence into account. Although sacrificing accuracy to some extent compared to the ANN model, the modified formula relies on a solid physical basis and its accuracy is enhanced significantly compared to the existing formulas in specifications or research papers.     

Investigation on Residual Strength and Failure Mechanism of the Ceramic/UHMWPE Armors after Ballistic Tests

In this paper, the ballistic damage mechanism and residual bearing capacity of ceramic/backing plate armor were investigated. First, a series of lightweight armors were prepared, consisting of ceramic and ultra-high molecular weight polyethylene fiber-reinforced resin matrix composite (UHMWPE) plates, and were wrapped in a high-strength fabric. Then, the ceramic/UHMWPE armors were hit by one or two bullets, and finally subjected to compression testing. The results showed that the main failure mode of integral ceramic/UHMWPE armors was ceramic brittle fracture. Many zigzag patterns on the compression curve indicated that the specimens had undergone the stages of crack propagation, ceramic fragment reorganization, plastic deformation of UHMWPE backing plate, interlaminar tearing, and overall fracture. The failure of spliced ceramic/UHMWPE armors was mainly due to the dislocation between ceramic sheets; the smooth compression curves indicated that there was no recombination of ceramic fragments and obvious interlayer debonding during the compression. Under the maximum load, each ceramic/UHMWPE armor with ballistic damage did not suddenly break and fail. The structure and thickness of ceramic plates all had an impact on residual strength: under the same structure, the greater the thickness, the greater the residual strength, but the relationship between them was not linear; under the same thickness, the residual strength of the spliced ceramic/UHMWPE armor was higher. The residual strength was also related to the number of shots: after two bullets hit, its value was only one-third of that after one bullet hit.     

Progressive Damage Numerical Modelling and Simulation of Aircraft Composite Bolted Joints Bearing Response

Finite element numerical progressive damage modelling and simulations applied to the strength prediction of airframe bolted joints on composite laminates can lead to shorter and more efficient product cycles in terms of design, analysis and certification, while benefiting the economic manufacturing of composite structures. In the study herein, experimental bolted joint bearing tests were carried out to study the strength and failure modes of fastened composite plates under static tensile loads. The experimental results were subsequently benchmarked against various progressive damage numerical modelling simulations where the effects of different failure criteria, damage variables and subroutines were considered. Evidence was produced that indicated that both the accuracy of the simulation results and the speed of calculation were affected by the choice of user input and numerical scheme.     

Structural,Optical and Mechanical Properties of Nanocrystalline Molybdenum Thin Films Deposited under Variable Substrate Temperature

Molybdenum (Mo), which is one among the refractory metals, is a promising material with a wide variety of technological applications in microelectronics, optoelectronics, and energy conversion and storage. However, understanding the structure–property correlation and optimization at the nanoscale dimension is quite important to meet the requirements of the emerging nanoelectronics and nanophotonics. In this context, we focused our efforts to derive a comprehensive understanding of the nanoscale structure, phase, and electronic properties of nanocrystalline Mo films with variable microstructure and grain size. Molybdenum films were deposited under varying temperature (25–500 °C), which resulted in Mo films with variable grain size of 9–22 nm. The grazing incidence X-ray diffraction analyses indicate the (110) preferred growth behavior the Mo films, though there is a marked decrease in hardness and elastic modulus values. In particular, there is a sizable difference in maximum and minimum elastic modulus values; the elastic modulus decreased from ~460 to 260–280 GPa with increasing substrate temperature from 25–500 °C. The plasticity index and wear resistance index values show a dramatic change with substrate temperature and grain size. Additionally, the optical properties of the nanocrystalline Mo films evaluated by spectroscopic ellipsometry indicate a marked dependence on the growth temperature and grain size. This dependence on grain size variation was particularly notable for the refractive index where Mo films with lower grain size fell in a range between ~2.75–3.75 across the measured wavelength as opposed to the range of 1.5–2.5 for samples deposited at temperatures of 400–500 °C, where the grain size is relatively higher. The conductive atomic force microscopy (AFM) studies indicate a direct correlation with grain size variation and grain versus grain boundary conduction; the trend noted was improved electrical conductivity of the Mo films in correlation with increasing grain size. The combined ellipsometry and conductive AFM studies allowed us to optimize the structure–property correlation in nanocrystalline Mo films for application in electronics and optoelectronics.     

Measurement of Shear Strengths of Cu Films Using Precise Chip Forming

The mechanical properties of thin films are under-researched because of the challenges associated with conventional experimental methods. We demonstrate a technique for determining the intrinsic shear strength and strain of thin films using a nano-cutting technique based on an orthogonal cutting model with precise control of the cutting system. In this study, electroplated Cu films with thicknesses of 1.5 μm and 5 μm and a sputtered Cu film with a thickness of 130 nm were fabricated to evaluate the mechanical strength. Experiments revealed a shear strength of approximately 310 MPa with a shear strain of 1.57 for the electroplated Cu film and a shear strength of 389 MPa with a shear strain of 2.03 for the sputtered Cu film. In addition, X-ray diffraction analysis was performed to correlate the experimental results.     

Tensile and Compressive Responses of Ceramic and Metallic Nanoparticle Reinforced Mg Composites

In the present study, room temperature mechanical properties of pure magnesium, Mg/ZrO₂ and Mg/(ZrO₂ + Cu) composites with various compositions are investigated. Results revealed that the use of hybrid (ZrO₂ + Cu) reinforcements in Mg led to enhanced mechanical properties when compared to that of single reinforcement (ZrO₂). Marginal reduction in mechanical properties of Mg/ZrO₂ composites were observed mainly due to clustering of ZrO₂ particles in Mg matrix and lack of matrix grain refinement. Addition of hybrid reinforcements led to grain size reduction and uniform distribution of hybrid reinforcements, globally and locally, in the hybrid composites. Macro- and micro- hardness, tensile strengths and compressive strengths were all significantly increased in the hybrid composites. With respect to unreinforced magnesium, failure strain was almost unchanged under tensile loading while it was reduced under compressive loading for both Mg/ZrO₂ and Mg/(ZrO₂ + Cu) composites.     

A Comparative Study on Hygric Properties and Compressive Strength of Ceramic Bricks

This article analyzes the results of capillary rise, compressive strength and water absorption tests on solid ceramic bricks from existing structures and demolition materials taken from 11 different structures. In addition (for more extensive interpretation and evaluation of porosity), tests were performed for the selected series of bricks using a mercury porosimeter (MIP) and a micro computed tomography (micro-CT). Contemporary bricks (2 series) were also evaluated for comparison purposes. The conducted tests indicate that bricks obtained from different sources are characterized by “individual” relation of compressive strength and porosity, and “individual” relation of water absorption coefficient and porosity. In addition, on the basis of the results obtained in the study, compared with the literature data, it can be deduced that ceramic bricks with a water absorption coefficient of less than 50 g/m²s^0.5 are characterized by a compressive strength of more than 80 MPa. As the research shows, the properties of bricks even from a single building can differ one from another, which can result in varying durability even within a single building. When choosing a material during the renovation or restoration of facilities, it is important to perform tests on the physical and mechanical properties of the original material, which will be reused.     

Experimental and Numerical Study on Interface Bond Strength and Anchorage Performance of Steel Bars within Prefabricated Concrete

This study investigates the interface bond strength and anchorage performance of steel bars within prefabricated concrete. Twenty-two specimens were designed and manufactured to study the interface bond behavior of deformed and plain steel bars under a larger cover thickness. Diameter of steel bars, strength grade of concrete, and anchorage length were considered influential factors. The finite element method (ABAQUS) was used for the validation of experimental results. The interface bond’s failure mechanism and the anchorage length in the prefabricated concrete under different concrete strength levels were explored and compared to national and international codes. A suitable value of the basic anchoring length for the prefabricated structure was recommended. The results show that the interface bond strength of prefabricated bridge members is directly proportional to the strength grade of the concrete, inversely proportional to the reinforcement diameter, and less related to anchorage length. The effect of the cover thickness of the surrounding concrete is negligible. Conversely, the bearing capacity of prefabricated bridge members depends on the strength of the concrete, the diameter of the steel bar, and the anchorage length. Furthermore, it is concluded that the mechanical bond strength accounts for 88% of the bond strength within prefabricated concrete.     

Metallic Glass-Reinforced Metal Matrix Composites: Design,Interfaces and Properties

When metals are modified by second-phase particles or fibers, metal matrix composites (MMCs) are formed. In general, for a given metallic matrix, reinforcements differing in their chemical nature and particle size/morphology can be suitable while providing different levels of strengthening. This article focuses on MMCs reinforced with metallic glasses and amorphous alloys, which are considered as alternatives to ceramic reinforcements. Early works on metallic glass (amorphous alloy)-reinforced MMCs were conducted in 1982–2005. In the following years, a large number of composites have been obtained and tested. Metallic glass (amorphous alloy)-reinforced MMCs have been obtained with matrices of Al and its alloys, Mg and its alloys, Ti alloys, W, Cu and its alloys, Ni, and Fe. Research has been extended to new compositions, new design approaches and fabrication methods, the chemical interaction of the metallic glass with the metal matrix, the influence of the reaction products on the properties of the composites, strengthening mechanisms, and the functional properties of the composites. These aspects are covered in the present review. Problems to be tackled in future research on metallic glass (amorphous alloy)-reinforced MMCs are also identified.     

Comparison of Physical and Thermal Properties of Mulching Films Made of Different Polymeric Materials

The development of polymer materials causes their huge expansion into various areas of everyday life, as well as plant and animal production. Their chemical resistance, good physical properties, and ease of processing result in an increasing use of this group of materials. Outdoor plant production both in open plantations and greenhouses requires various types of materials supporting the vegetation process as well as protecting against pests and weeds. A large group here are various types of materials used for covers of field crops, the main role of which is to prevent uncontrolled and excessive growth of weeds and thus reduce the use of herbicides as plant protection products. Cover films also have other important functions, such as reducing direct water evaporation, better moisture retention around the root system, increasing soil temperature (faster vegetation), etc. However, as always, the problem of introducing new material into agriculture production and the difficulty of its disposal arises. In recent times, farmers’ interest in various forms of mulch to protect crops and increase yields has grown significantly. In the publication, the authors attempted to analyze selected commercial properties, but also mulch produced on a laboratory scale, based on biodegradable and petroleum-derived materials.     

The Relationship between Microstructure and Fracture Behavior of TiAl/Ti2AlNb SPDB Joint with High Temperature Titanium Alloy Interlayers

In this paper, spark plasma diffusion bonding technology was employed to join TiAl and Ti₂AlNb with high temperature titanium alloy interlayer at 950 °C/10kN/60 min, then following furnace cooling at cooling rate up to 100 °C/min. After welding, the joint was aging heat-treated at 800 °C for 24 h. The microstructure and the elements diffusion of the TiAl/Ti₂AlNb joint was analyzed by field emission scanning electron microscopy (FESEM) with EDS. Moreover, the tensile properties of the joint were tested at room temperature, 650 °C, and 750 °C. The results show that the spark plasma diffusion bonding formed a high quality TiAl/Ti₂AlNb joint without microcracks or microvoids, while also effectively protecting the base metal. Significant differences in the microstructure of the joint appeared from TiAl side to Ti₂AlNb side: TiAl BM (Base Metal) → DP(Duplex) and NG (Near-Gamma) → α₂-phase matrix with needle-like α-phase → bulk α₂-phase → needle-like α-phase → metastable β-phase → Ti₂AlNb BM. After heat treatment at 800 °C for 24 h, the microstructure of the TiAl side and the interlayer region did not change, but the density and size of the needle-like α-phase in region 3 increased slightly. The microstructure of Ti₂AlNb near the weld changed obviously, and a large number of fine O phases are precipitated from the metastable β phase matrix after heat treatment. Except for the Ti₂AlN near-interface region, the effect of heat treatment on the microstructure of the joint is not significant. The microhardness of the joint is in the shape of a mountain peak. The maximum microhardness at the interface is above 500 HV, and it is significantly reduced to 400 HV after heat treatment. The fracture of the joint occurred at the interface at room temperature, 650 °C, and 750 °C. with the tensile strength 450 MPa, 540 MPa, and 471 Mpa, respectively, and mainly showing brittle fracture.     

The Effect of Yttria Content on Microstructure,Strength, and Fracture Behavior of Yttria-Stabilized Zirconia

Yttria-stabilized zirconia (YSZ) is well-known as a material with perfect mechanical, thermal, and electrical properties. It is used for manufacturing various high-temperature components for aerospace and energy generation, as well as wear- and corrosion-resistant devices in medicine. This work investigated the effect of a Y₂O₃ addition to ZrO₂ on the microstructure and mechanical properties of YSZ ceramics produced by one sintering schedule. ZrO₂ ceramics doped with 3, 4, 5, 6, 7, and 8 mol% Y₂O₃ (designated 3YSZ through to 8YSZ) were prepared by using conventional sintering at 1550 °C for 2 h in argon. The effect of yttria content was analyzed with respect to grain size, morphology of the microstructural features, phase composition, parameters of fracture surface, and flexural strength. The 7YSZ ceramics sintered at 1550 °C for 2 h showed the highest level of flexural strength due to the formation of the fine-grained microstructure containing mainly the monoclinic and tetragonal zirconia phases. The fracture micromechanism in the studied YSZ ceramics is discussed.     

The Mechanism of Fracture and Damage Evolution of Granite in Thermal Environment

In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shear cracks steadily declined. Furthermore, it was found that when temperature rises, the number of early tensile cracks grows. This study develops a fracture prediction system for rock engineering in high-temperature conditions.     

Advanced Estimation of Compressive Strength and Fracture Behavior in Ceramic Honeycombs by Polarimetry Measurements of Similar Epoxy Resin Honeycombs

Finding a non-destructive characterization method for cellular ceramics’ compressive strength and fracture behavior has been a challenge for material scientists for years. However, for transparent materials, internal stresses can be determined by the non-destructive photoelastic measurements. We propose a novel approach to correlate the photoelastic stresses of polymer (epoxy resin) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs were 3D-printed via stereolithography with varying structure angles from −35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading revealed regions of excess stress, which directly corresponded to the initial fracture points of the ceramic honeycombs. These honeycombs were made by a combination of 3D printing and transfer molding from alumina. The photoelastic stress distribution was much more homogeneous for angles of a smaller magnitude, which led to highly increased compressive strengths of up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we showed that we could use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.     

Impact of Particle Size of Ceramic Granule Blends on Mechanical Strength and Porosity of 3D Printed Scaffolds

3D printing is a promising method for the fabrication of scaffolds in the field of bone tissue engineering. To date, the mechanical strength of 3D printed ceramic scaffolds is not sufficient for a variety of applications in the reconstructive surgery. Mechanical strength is directly in relation with the porosity of the 3D printed scaffolds. The porosity is directly influenced by particle size and particle-size distribution of the raw material. To investigate this impact, a hydroxyapatite granule blend with a wide particle size distribution was fractioned by sieving. The specific fractions and bimodal mixtures of the sieved granule blend were used to 3D print specimens. It has been shown that an optimized arrangement of fractions with large and small particles can provide 3D printed specimens with good mechanical strength due to a higher packing density. An increase of mechanical strength can possibly expand the application area of 3D printed hydroxyapatite scaffolds.     

Bonding Interface and Repairability of 3D-Printed Intraoral Splints: Shear Bond Strength to Current Polymers,with and without Ageing

This in-vitro study investigates the bonding interfaces reached by the conditioning of a splint material additively manufactured by digital light processing (AM base) as well as the shear bond strength (SBS) of resins bonded to these surfaces (repair material). Therefore, the AM base was either stored in dry for 12 h or wet environment for 14 days to simulate ageing by intraoral wear. The dry and wet group was bonded after physical and/or chemical conditioning to cylinders made from polymethylmethacrylate or four novel polymers allowing splint modifications. Blasted and methylmethacrylate (MMA)-conditioned Polymethylmethacrylate (PMMA) bonded to PMMA acted as the gold standard. The surface profiles revealed highest differences of Ra towards the gold standard in AM base conditioned with other than MMA after sandblasting. The adhesively bonded repair materials of the wet AM base were further aged in wet environment for 14 days. The SBS of the gold standard (25.2 MPa and 25.6 MPa) was only reached by PMMA bonded to blasted and MMA-conditioned AM base after dry (22.7 MPa) and non-conditioned after wet storage (23 MPa). Four repair materials failed to reach the threshold of 5 MPa after dry storage and three after wet storage, respectively. Non-conditioned AM base revealed the highest risk for adhesive fractures when using other resins than PMMA.     

Damage Evolution and Fracture Behavior of C/SiC Minicomposites with Different Interphases under Uniaxial Tensile Load

In this paper, the tensile damage and fracture behavior of carbon fiber reinforced silicon carbide (C/SiC) minicomposites with single- and multiple-layer interphases are investigated. The effect of the interphase on the tensile damage and fracture behavior of C/SiC minicomposites is analyzed. The evolution of matrix cracking under the tensile load of the C/SiC minicomposite with a notch is observed using the digital image correlation (DIC) method. The damage evolution process of the C/SiC minicomposite can be divided into four main stages, namely, (1) an elastic response coupled with partial re-opening of thermal microcracking; (2) multiple matrix microcracking perpendicular to the applied loading; (3) crack opening and related fiber/matrix, bundle/matrix, and inter-bundle debonding; and (4) progressive transfer of the load to the fibers and gradual fiber failure until composite failure/fracture. On the fracture surface, a large number of fibers pulling out of the samples with both single-layer and multi-layer interphases can be clearly observed.