Strength Σ0 Research Articles

Strength characterization and lifetime prediction of dental ceramic materials

ObjectiveTo determine the Weibull modulus m, the characteristic strength σ0,the subcritical crack growth (SCG) parameters (n &A*) as well as the lifetime durability of three dental ceramic materials in water: a polycrystalline yttria-stabilized zirconia (Zenostar MT O, YSZ, Ivoclar Vivadent/Wieland, Germany), a lithium disilicate glass ceramic (IPS e.max CAD, LD, Ivoclar Vivadent, Liechtenstein), and a zirconia-containing lithium silicate glass ceramic (Celtra Duo, ZLS, Dentsply Sirona Inc, USA). Methods30 specimens (Ø12 mm × 0.9 mm thickness) of each material were fabricated. The biaxial ring-on-ring bending tests at four stress rates σ˙ (100, 10, 1, 0.1 MPa/s) were performed in water for all three ceramics. The results were used to determine the Weibull and SCG parameters, and to plot the Strength-Probability-Time (SPT) diagram. ResultsYSZ showed the highest m (12.5) and highest σ0 (542 MPa), while the values for the glass ceramic materials were lower: for LD m = 4.7, σ0 = 407 MPa, and for ZLS m = 2.7, σ0 = 279 MPa. The n for YSZ, LD and ZLS in water were 31.1, 13.7 and 16.6, respectively. The strength of YSZ decreased by 50% within a simulated period of 10 years, and for the glass ceramic materials the decrease was up to 80%. SignificanceDetermining the Weibull and SCG parameters from the constant stress rate testing is an efficient methodology for ranking materials in terms of durability and longevity.

Choosing the Rational Heat Treatment Conditions for High-Strength Cold-Resistant Weldable Steel with Yield Strength of more than 600 N/mm2

Rational heat treatment conditions for the new weldable cold-resistant steel grade 20G2SMRA ensuring a guaranteed yield strength σ0,2 ⩾ 600 N/mm2 combined with the lowtemperature impact strength KCV-60 ⩾ 50 J/cm2 have been searched. The effect of various quenching and tempering conditions on the steel microstructure parameters, hardness, and impact strength at a temperature of -60 °C has been studied. The dependencies of the microstructure parameters, hardness (HV1), and impact strength (KCV-60) on the quenching and subsequent tempering temperature are represented. Rational heat treatment conditions have been found for a new weldable cold-resistant steel with high yield strength.

Deformation Behavior of C15E + C Steel under Different Uniaxial Stress Tests

In this paper, the mechanical properties of the material that define its mechanical behavior are experimentally investigated. All performed experimental tests and analyzes are related to C15E + C steel. The tested material was delivered as cold drawn round bar. It is usually used in mechanical engineering for design of low stressed components. Experimentally obtained results relate to the maximum tensile strength, yield strength, creep behavior, and uniaxial fully reversed high cyclic fatigue. Results representing mechanical properties are shown in the form of engineering stress–strain diagrams, while creep behavior of the material at different temperatures and different stress levels is displayed in the form of creep curves. Tests representing uniaxial cyclic fully reversed mechanical fatigue at constant stresses and room temperature in air are shown in the form of fatigue-life (S−N) diagram. Some of the experimental results obtained are as follows: ultimate tensile strength (σm(20 °C/500 °C)=(598/230) MPa), yield strength (σ0.2(20 °C/500 °C)=(580/ 214 ) MPa ), modulus of elasticity (E(20 °C/500 °C)=(213/106) GPa), and fatigue limit (σf(20 °C, R=−1)=250.83 MPa). The fatigue tests were performed at frequency of 40 Hz and at room temperature (20 °C) in air, with stress ratio of R=−1.

Microstructure evolution and mechanical properties of AlxCoCrFeNi high-entropy alloys by laser melting deposition

AlxCoCrFeNi (x = 0, 0.2, 0.45, 0.7 and 1) high entropy alloys (HEAs) have been successfully synthesized by laser melting deposition (LMD). It is found that the microstructure of LMD-CoCrFeNi HEA with increasing the content of Al has been transformed from a single face-centered cubic (FCC) phase to mixture of FCC + BCC duplex phases, and then to body-centered cubic (BCC/B2) phases. The addition of Al (Al0.2, Al0.45 and Al0.7) remarkably improved the yield strength σ0.2 (from 138 MPa to 185 MPa, 262 MPa and 771 MPa) and the tensile strength σt (from 634 MPa to 675 MPa, 863 MPa and 1171 MPa) of the samples, with the prize of plasticity decrease from 46% to 45%, 41% and 11% in tension. This work provides an approach of LMD-fabricated CoCrFeNi-based HEAs with different Al addition to accommodate the microstructure and mechanical properties, and insights into the correlation of mechanical properties with the solid solution strengthening or/and the precipitation of hardening phase.

High ductility and strong work-hardening behavior of Zn modified as-hot-rolled Al–Mg sheets

High ductility combining with relative high strength is of great significance for the application of Al–Mg alloys. In this study, excellent ductility and moderated strength are obtained in the as-hot-rolled Al-9.2Mg-0.5Zn sheet, with ultimate tensile strength (σb), yield tensile strength (σ0.2) and elongation (δ) are respectively 434 ± 5 MPa, 228 ± 2 MPa and 48 ± 2%. High ductility of the as-hot-rolled Al-9.2 Mg-xZn (0-1.5 wt%) sheets can be ascribed to their strong work-hardening abilities, which increase firstly and then decline with higher Zn content. The highest work-hardening component (n), work-hardening capacity (Hc) and the initial work-hardening rate (θ0) in the Al-9.2Mg-0.5Zn sheet are 0.428, 1.793 and 3496 MPa, respectively. The microstructures of the Al–Mg–Zn sheets are characterized by electron backscattered diffraction (EBSD), transmission electron microscope (TEM), X-ray diffraction (XRD) and scanning electron microscope (SEM). Low density of pre-existing dislocations (PDs), random grain orientations and reduced stacking fault energy (SFE) contribute to the strong work-hardening capacity and lead to desirable ductility in the as-hot-rolled Al–Mg–Zn sheets. However, numerous precipitates with an uneven distribution are harmful for work-hardening and thus lead to the reduced ductility in the Al–Mg sheet with high Zn content.

Improvement in irradiation resistance of FeCu alloy by pre-deformation through introduction of dense point defect sinks

The irradiation resistance of pre-deformed FeCu alloy was studied using a 3 MeV Fe ion irradiation experiment at room temperature in comparison with that of the as-received sample. Nanoindentation and atom probe tomography (APT) were used to characterize the mechanical properties and solute distribution. The stress–strain curve obtained by nanoindentation shows that the yield strength (σ0.2) of the pre-deformed sample is unexpectedly reduced with an increase in the irradiation dose to five displacements per atom (dpa). We suggest that it results both from the decrease in the dislocation density and the suppression of defects during irradiation. APT shows that the nucleation of the Cu cluster is suppressed; however, its growth is promoted in the pre-deformed sample, resulting in the formation of sparse and coarse clusters at 1 dpa irradiation. These coarse Cu clusters were then unexpectedly refined to finer grains with an increase in the irradiation dose to 5 dpa. Theoretically, the improvement in the resistance to irradiation in the pre-deformed sample is attributed to the dense point-defect sinks, that is, the dislocations and grain boundaries introduced by pre-deformation. In addition, the contributions of the dislocations and grain boundaries to the sink strength are estimated for both the as-received and pre-deformed samples. The results indicate that dislocations, rather than grain boundaries, play a major role after deformation.

Bond strength between concrete substrate and repair mortar: Effect of fibre stiffness and substrate surface roughness

This study investigated the effects of fibre stiffness, substrate surface roughness, and surface angle on the bond strength between concrete substrate and repair mortar. The substrate surface was repeatedly treated with high-pressure water to obtain various roughness values. Steel and carbon fibres played the role of rigid and flexible fibres, respectively, in the repair mortar. The bond strength (including both adhesion and friction components) was evaluated via slant shear tests with various slant shear angles. Adhesion was examined using the Mohr–Coulomb approach to reflect pure bond behaviour. The results indicate that bond strength (σ0,av, fibre type 0) increased as the roughness increased; further, removing the floating pulp layer can improve adhesion. However, after removal and with increasing substrate surface roughness (fibre type 0), there was no significant change in adhesion. As the roughness increased, the number and length of exposed steel fibres increased. The steel fibres maintained their original shape in the mixture and significantly enhanced adhesion because of the dowel and second-order dowel effects. In contrast, carbon fibres were severely deformed in the mixture and showed decreased adhesion owing to pores existing at the interface. The synergy between steel and carbon fibres can enhance the ultimate load capacity of steel fibres under axial compression. This enhances the dowel effect, thereby improving adhesion.

Electronic structure characteristics of Fe-6.5 wt%Si alloy doped with rare earth elements and its effect on mechanical properties

Effects of rare earth RE (Y, La, Ce) element doping on electronic structure of Fe-6.5 wt%Si alloy and the influence mechanisms of RE doping on mechanical properties of the alloy were studied via first-principles calculation based on density functional theory (DFT). The results show that there exists significant electron transfer between solid solution RE atom and Fe, Si atoms, which leads to a significant change on the gain/loss quantity of electrons and the bonding properties of atoms, thus changing the covalent interaction of Fe–Fe bonds and Si–Fe bonds, reducing the ordered degree and improving the deformability of Fe-6.5 wt%Si alloy. With an increase of RE content, the tensile deformability at 400 °C of as-cast alloy specimens presented a change rule of first increasing and then decreasing, and the elongation to failure increased from about 7% of non-RE-doped specimens to a maximum of about 22–23% of RE doped specimens. The content of Y, La, and Ce is about 59 ppm, 38 ppm, and 75 ppm respectively (atom fraction, called reasonable content) when the deformability improvement effect of RE is better, the RE exceeding reasonable content tended to enrich near grain boundaries and caused inter-granular brittleness. Through a comparative study between non-RE-doped alloy and RE (Ce) doped alloy, it was found that there was no significant difference in microstructure and crystal structure between the warm-rolled samples of two alloys, but Ce doping reduced tensile yield strength σ0.2 from 1618.5 MPa to 1515.3 MPa and increased elongation to failure from 0.67% to 0.80% at room temperature of warm-rolled samples by weakening covalent interaction of some bonds, which helps to improve cold rolling deformability of samples, and Ce doping caused no obvious damage to magnetic properties of the thin sheet after cold rolled.

Comparison of in situ nanocrystals, Sr and nanocrystals + Sr manipulating microstructures and mechanical properties of eutectic Al–Si13.0–Cu5.0–(Ni2.0)–Mg0.6 alloy

Trace in situ nanocrystals crystallized from metallic glasses as innovative microstructure manipulation agents were proposed to manipulate the multilevel microstructure configuration of eutectic Al–Si13.0–Cu5.0–Mg0.6 alloy. And the manipulation effect by nanocrystals for different times was compared with Sr, nanocrystals + Sr and Ni alloying. The calculations indicated that NiTi nanocrystals had an ideal mismatch with α-Al and silicon; thus, nanocrystals can stimulate their nucleation and hinder their growth. Sr and Ni alloying were found to only refine the silicon phases, but nanocrystals refined both α-Al and silicon phases. Moreover, the inhibition of nanocrystals and Sr was verified. After the manipulation by nanocrystals for 20 min, the optimum microstructure configuration and mechanical properties were realized. The results showed that the size of α-Al was reduced by 86.7%, and the size and aspect ratio of eutectic silicon were decreased by 27.7% and 50.0% compared with that of the unmanipulated alloy. Primary silicon was distributed more evenly and reduced in number. In addition, the size of Al2Cu and Mg2Si was decreased by 57.7% and 90.6%. Accordingly, a prominent microstructure configuration comprised of refined α-Al, silicon phases and precipitations was established successfully via nanocrystals. Moreover, the ultimate tensile strength (UTS) and fracture strain (FS) were increased by 17.8% and 73.3% compared with that of the unmanipulated alloy at ambient temperature, and the yield strength (σ0.2) and UTS were increased by 21.5% and 14.4% at 250 °C. The specific strengthening mechanisms were revealed, as well. Therefore, in situ nanocrystals have great application potential and developmental value.

Determination of surface mechanical property and residual stress stability for shot-peened SAF2507 duplex stainless steel by in situ X-ray diffraction stress analysis

In this study, SAF2507 duplex (austenite–ferrite) stainless steel was processed by shot peening. The depth–profile variations of the stress state and work hardening in the shot-peened layer were investigated by X-ray diffraction and microhardness tests. The evolutions of surface morphology and microstructure were investigated using scanning and transmission electron microscopy. The stress–strain relations of the shot-peened surface and surface residual stress relaxation caused by cyclic stresses were experimentally determined by in situ X-ray diffraction stress analysis combined with tensile tests. Results showed that shot peening (SP) has induced severe plastic deformation in the surface layer, with the attendant work hardening and high compressive residual stresses (CRS). Nevertheless, there were incompatibilities in plastic deformation between the phases, and more property improvements represented by higher CRS, peak breadth and microhardness were conferred into austenitic phases. SP notably enhanced the surface yield strength of this two-phase alloy. The surface yield strength σ0.2 of ferrite and austenite were around 780 and 1100MPa after SP, which were 59% and 104% respectively higher than that of the untreated surface. The surface stress relaxation under cyclic tensile loadings consisted of a two-stage process. The surface residual stresses relaxed dramatically within the first cycle (N=1), then decreased linearly with the logarithm of loading cycles (N>1). The more severely deformed microstructures in austenite resulted in higher surface yield strength and contributed to higher cyclic stability of residual stress.

Microstructure evolution and mechanical properties of Al0.4CoFeNiTi0.6 dual-phase high entropy alloy

The influence of annealing treatment on the microstructure evolution and mechanical properties of a new multi-principal component high entropy alloy (HEA) with dual-phase, Al0.4CoFeNiTi0.6, prepared by arc-melting, was investigated in detail. The as-cast alloy was composed of simple BCC and FCC phases which were further confirmed to be B2 and L12 structures. The yield strength (σ0.2), fracture strength and plastic strain of the as-cast alloy are 2085 MPa, 2136 MPa and 10.3%, respectively. Following annealing treatment, a large number of shortly rod-like phases are precipitated from the ordered BCC phase. The as-annealed alloy projects a decrease of ~33% in yield strength and a decrease of ~8% in fracture strength. However, the plastic strain is increased from 10.3 to 21%. The hardness increased from 467 HV to 548 HV, indicating that the alloy exhibits excellent temper-resistant softening properties.

Length-scale dependent deformation, strengthening, and ductility of fcc/fcc Ni/Al nanolaminates using micropillar compression testing

The deformation and strengthening behaviors of face-centered cubic/face-centered cubic (fcc/fcc) nickel (Ni)/aluminum (Al) nanolaminates were systematically investigated in uniaxial compression tests using micropillars with a varied range of individual layer thickness h from 5 nm to 100 nm. The deformation behavior of micropillar samples of Ni/Al nanolaminates was strongly dependent on the individual layer thickness of Ni and Al, where at larger h the deformation of micropillars took place first by plastic deformation of the Al layers and proceeded to dislocation pileup–based Hall–Petch (H-P) strengthening, which further nucleated in the Ni layers. The deformation behavior of the Ni/Al nanolaminates transitioned from dislocation-dominated homogeneous co-deformation with multiple shearing in Ni and Al layers and grain boundary–mediated massive fractures in the Ni layers at larger h to stress-concentrated broken interfaces and valleys with plastic barreling due to layer shearing and smaller fractures in the Ni and Al layers at smaller h. With decreasing h from 100 nm down to 5 nm, the Ni/Al micropillars exhibited a gradual transition from lower to higher strain hardening, and the strain-hardening rate reached a peak at h = 20 nm; while it started declining with further decreasing of h. The yield strength (σ0.2%) and flow strength (σ8%) of the Ni/Al micropillars reached the peak of ~1.93 GPa and ~2.35 GPa, respectively, with decreasing h to 10 nm. The confined layer slip (CLS) strengthening mechanism operated well at h = 10 nm, whereas H-P strengthening model was applicable for h = 20–100 nm, and surprisingly the strengthening at h = 5 nm was independent of h. Interestingly, significant strain softening was observed at h = 5 nm due to the severe plastic deformation at the broken interfaces, interfacial sliding of layers, and defects related to the presence of intermixed Ni and Al layers at the interface, and valleys between the islands of stacked constituent layers.

Optimization of Heat Treatment of Steel with Enhanced Thermal Resistance

The work is dedicated to the development of the optimal technological process for the manufacture of hot stamping dies and die casting molds made of steel grade 4X5MF1С, in order to ensure the required performance characteristics. The mode of hardening heat treatment of this steel grade was established, which allows to recommend it as a heat-resistant structural material for metal products with the required yield strength σ0.2 within 750 to 1000 MPa.

Effect of pre-annealing on microstructure, mechanical properties and current-carrying properties of Bi-2212 wires

Abstract In order to solve the problem of excessive porosity of Bi-2212 Cable in Conduit Conductor (CICC) after the overpressure heat treatment, which leads to a significant decrease of mechanical stability of the conductor, a pre-annealing of Bi-2212 wires with a total pressure of 50 bar has been carried out in this paper. After the pre-annealing, the density of oxide cores of Bi-2212 wires was close to the theoretical density, which avoided the problem of diameter reduction of the wires in Bi-2212 CICC during overpressure heat treatment. At the same time, the mechanical properties, microstructures and current carrying properties of pre-annealed wires have been also analyzed. It showed that after pre-annealing, the Bi-2212 wires had not only high yield strength σ0.2, which reached 167 Mpa, but also great tensile strainse, which reached 7.4 %. High yield strength of the wires could effectively avoid serious scratches on the surface of wires during the preparing process of Bi-2212 CICC. Large tensile strain of the wires could prevent the crack of the wires caused by large compressive deformation or twisting deformation of the wires during preparation of Bi-2212 CICC, so that the conductors with smaller pitch and low hysteresis loss could be prepared. In addition, the phase composition of oxide cores in Bi-2212 wires did not change obviously during the pre-annealing process, but the crystallinity of Bi-2212 powder of the cores increased significantly, which was beneficial to the simultaneous melting of Bi-2212 powder of the cores during the overpressure heat treatment and the improvement of the content of Bi-2212 phase of the final wires. As a result, the current carrying capacity of the wires was slightly improved, and its engineer critical current density (Je) reached 825 A/mm2 (4.2K, 12T), which could meet the requirements of future fusion systems. In summary, it is expected that Bi-2212 CICC with less surface defects of the wires, low hysteresis loss, high filling ratio and excellent current-carrying performance can be obtained by the pre-annealing method.

Enhanced mechanical properties of ZrO2-Al2O3 dental ceramic composites by altering Al2O3 form

ObjectivesThis study evaluates the difference in physical and mechanical properties of ZrO2 ceramics, commonly used in dental applications, altered by three different forms of Al2O3 content; microparticles (m), nanoparticles (n), and microfiber (f). MethodsThree different types of ZrO2–Al2O3 composites were formed using microparticle (m), nanoparticle (n), or microfibre (f) forms of Al2O3. The physical and mechanical properties such as sintering shrinkage, relative density, Vickers hardness, fracture toughness, and biaxial strength were evaluated. A Weibull analysis was performed to assess the strength reliability of the specimens. All data were calculated using the t-test and ANOVA. ResultsThe sintering shrinkage and relative density of all ceramic composite groups were decreased with the addition of Al2O3. The mechanical properties of ZrO2–Al2O3 (f) composite were higher than that of ZrO2–Al2O3 (m) composite and ZrO2–Al2O3 (n) composite. The maximum hardness, fracture toughness, and biaxial flexural strength were observed for 10 vol% of Al2O3 fibre. When the content of Al2O3 fibre in the matrix was increased above 20 vol%, agglomeration occurred and resulted in a decrease of hardness and toughness. The Weibull modulus value of the ZrO2–Al2O3 (f) composite was the lowest compared to that of other groups. However, characteristic strength (σ0) of ZrO2–Al2O3 (f) the highest value. SignificanceThe current study demonstrated that the addition of right amount of Al2O3 microfibre into the ZrO2 matrix enhanced the mechanical properties of ZrO2-Al2O3 (f) composite, which would be favourable for dental applications.

Influence of minimal extended firing on dimensional, optical, and mechanical properties of crystalized zirconia-reinforced lithium silicate glass ceramic

This study should evaluate the influence of extended firing on the dimension, optical properties and flexural strength of a fully crystalized zirconia-reinforced lithium-silicate ceramic (ZLS) for single tooth restorations. Methods150 ZLS (Celtra Duo) and 30 lithium disilicate (LDS, IPS e.max CAD) specimens (17 × 4 × 1 mm) were milled in a standard device (Cerec MC XL). The ZLS specimens were distributed equally to five experimental groups (polished, standard firing [IFU], and three extended firings). LDS acted as a control group. The extended firings of ZLS addressed the first glaze firing (EF1) as well as the subsequent glaze firing (EF2) by a controlled overheating of +15 °C during the holding time. Color was measured with a digital spectrophotometer (Shadepilot), and dimensions with a digital calliper, before and after firing. A color change of ΔE ≥1.5 and a volume change of ±0.5% was regarded as clinical relevant.All specimens underwent a three-point-bending test to calculate flexural strength and Weibull statistics. ResultsThe color change after firing of ZLS (ΔE value; mean = 1.06; SD = 0.53) exceeded the perceptible threshold of ΔE ≥1.5 in 20% of IFU (mean = 1.18) and EF1+2 (mean = 0.95), 23% of EF1 (mean = 1.11), and 10% of EF2 (mean = 0.99) specimens with no statistical difference between the experimental groups. In 80% of IFU, 63% of EF2, 56% of EF1, and 33% of EF1+2 vol. change after firing exceeded ±0.5%. Characteristic Weibull strength σ0 and modulus m of polished ZLS specimen was affected by firing in IFU (σ0 = 314.35 MPa; m = 5.81), EF1 (σ0 = 324.68 MPa; m = 5.67), EF2 (σ0 = 326.4 MPa; m = 7.24), and EF1+2 (σ0 = 357.15 MPa, m = 3.69). LDS revealed σ0 = 405.7 MPa; m = 8.04, and polished ZLS σ0 = 219.3 MPa; m = 8.9 with statistical significant difference of the flexural strength between all fired ZLS experimental groups towards “as polished” as well as LDS. ConclusionFiring of ZLS led to changes in dimensions, color, and Weibull modulus. Firing increases flexural strength, but minimal temperature extension also increases materials inhomogeneity and risk of failure. The findings call for further investigations towards firing behavior of ZLS and its clinical relevance for restorations.

Double-side friction stir welding of thick magnesium alloy: microstructure and mechanical properties

ABSTRACTA two-step double-side friction stir welding (DS-FSW) technique was proposed to join 20 mm thick Mg–Y–Nd magnesium alloy plates. FSW was first carried out on one side of the butt joint, and then the plates were left-right reversed for the other side welding. The DS-FSW joint was free of defects and the weld nugget zone (NZ) showed fine equiaxial grains. An overlap zone with ultrafine grain (∼2.19 µm) and dispersive particles existed between the two welding tracks, beneficial to the integrity of the joint. The ultimate tensile strength (σUTS), yield strength (σ0.2), and elongation rate (δ) of the joint were 277. 6, 204.1 MPa, and 7.27%. A high joint efficiency (σUTS ratio between the joint and parent material) was achieved at ∼82.6%.

The Effect of Censoring on the Statistical Evaluation of Composite-to-Composite Bond Strength.

To determine the effect of Weibull analysis with censoring of cohesive failures on the evaluation of the effect of surface treatment and adhesive on the microtensile composite-composite bond strength. Surfaces of Filtek Z250 (3M Oral Care) specimens aged in distilled water for five months at 37°C were ground with SiC paper P320 or air abraded with Al2O3 and built up with the same composite using Optibond FL (OPF, Kerr), Clearfil SE Bond (CSE, Kuraray Noritake) and Gluma Comfort Bond (GLU, Kulzer) adhesives. After sectioning and trimming, the specimens were stored at 37°C in distilled water for 24 h and then tested in a microtensile bond strength setup. Complete datasets of all strength data and adhesive datasets containing adhesively failed specimens were analyzed with a one-way Welch ANOVA at α = 0.05 and compared with the results of Weibull analysis applied on complete and adhesive datasets as well as complete datasets right censored for cohesive failures. Weibull shape (m) and scale (σo) parameters were estimated using the maximum likelihood method and used to calculate bond strength (σ0.10) at 10% probability of failure as a measure of system performance. The surface morphology was studied using light and scanning electron microscopy. While ANOVA indicated a significant effect of surface treatment and non-significant effect of the adhesive, the Weibull analysis results depended on bond strength characteristics and censoring. The scale parameter of the complete dataset indicating a significant effect of surface treatment for all adhesives became statistically non-significant for CSE after censoring. When this effect was evaluated by σ0.10, the non-significant effect of surface treatment for OPF and GLU became statistically significant due to censoring. The effect of the adhesive evaluated by the scale parameter was non-significant both for surfaces as well as complete and censored datasets. On the other hand, s0.10 suggested significant differences between adhesives on the ground surface for complete datasets which became statistically non-significant for the censored datasets. This study indicates that the results of statistical evaluation of bond strength can be affected not only by the experimental set-up and statistical model but also the bond strength characteristics and the manner in which the strengths of cohesively failed specimens are included in calculations.

High-speed Deformation and Failure of Titan Alloy

The paper presents the results of a study of the dynamic properties of 3M titanium alloy under tension, carried out using the Kolsky method, as well as the results of determining the spall strength obtained using a VISAR laser interferometer. The experiments using the split Hopkinson pressure bar were carried out in the range of strain rates of 700 - 1500 s_1. In this experiments, dynamic strain diagrams were obtained, according to which the yield strength σ0.2 and the tensile strength were determined. The yield strength of the studied material increases with increasing strain rate from 700 MPa to 800 MPa. Since the 3M alloy does not experience hardening with increasing strain, fracture begins at stress close to yield strength. The tensile strength of this alloy under uniaxial tension (temporary tensile strength) also grows slightly from 700 MPa to 800 MPa with increasing strain rate. The ultimate plastic fracture characteristics of a titanium alloy (elongation and relative narrowing after rupture) are practically independent of the strain rate. In plane-wave experiments, spall strength was studied in the range of strain rates of 2 · 104 - 5 · 104s-1. The obtained values of spall strength lie in the range of 1.6 - 4 GPa, which significantly exceeds the values obtained under static loading and the values obtained in experiments using the Kolsky method, which is apparently associated with both the influence of the strain rate and the influence volumetric stress state in a plane-wave experiment.

Failure Prediction of AISI 420 Martensitic Stainless Steel Using the Theory of Critical Distances

This work aims to evaluate the capability of the theory of critical distances (TCD) to predict the static failure of U-notched AISI 420 martensitic stainless steel specimens with different geometric features under pure bending loading. Theoretical estimates of the stress intensity factor during fracture onset were calculated according to the line (LM) and point methods (PM), which consider the characteristic length L, inherent strength σ0, and notch tip radius ρ. Initially, L and σ0 were determined on the basis of the material’s properties (i.e., fracture toughness KIc and ultimate tensile strength σu,t), resulting in imprecise estimates. Conversely, L and σ0 determined using the appropriate analysis of linear–elastic stress fields ahead of notches with different sharpness provided highly accurate predictions. The microscopic study of fractured specimens ensured better comprehension of the results. Moreover, the accurate values of L and σ0 were used to predict the failure of V-notched specimens.