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Inorganic ferroelectrics have long dominated research and applications, taking advantage of high piezoelectric performance in bulk polycrystalline ceramic forms. Molecular ferroelectrics have attracted growing interest because of their environmental friendliness, easy processing, lightweight, and good biocompatibility, while realizing the considerable piezoelectricity in their bulk polycrystalline forms remains a great challenge. Herein, for the first time, through ring enlargement, a molecular ferroelectric 1‐azabicyclo[3.2.1]octonium perrhenate ([3.2.1‐abco]ReO4) with a large piezoelectric coefficient d33 up to 118 pC/N in the polycrystalline pellet form is designed, which is higher than that of the parent 1‐azabicyclo[2.2.1]heptanium perrhenate ([2.2.1–abch]ReO4, 90 pC/N) and those of most molecular ferroelectrics in polycrystalline or even single crystal forms. The ring enlargement reduces the molecular strain for easier molecular deformation, which contributes to the higher piezoelectric response in [3.2.1‐abco]ReO4. This work opens up a new avenue for exploring high piezoelectric polycrystalline molecular ferroelectrics with great potential in piezoelectric applications. [ABSTRACT FROM AUTHOR]

The isothermal planar‐biaxial fatigue behavior was studied for two different disk batches of nickel‐base superalloy Inconel 718 using cruciform specimens at 400°C and 630°C under equi‐biaxial and shear loading. Additionally, non‐proportional tests were performed. The planar‐biaxial test results were compared with uniaxial reference tests using the von Mises equivalent strain hypothesis, a shear strain parameter of the critical plane, and a modified crack‐opening‐displacement strain range approach. Additionally, the crack initiation mechanism was analyzed. Using a modified crack‐opening‐displacement strain range approach, the low‐cycle fatigue lifetimes of the proportional planar‐biaxial tests (i.e., lifetimes up to 40,000 cycles) were described within a scatter band of two. Thus, it was better than using the equivalent strain of von Mises or a shear strain parameter. The fatigue crack initiation took place at oxidized primary carbides at the surface. The crack paths were presented. Highlights: IN718 showed cyclic softening and final stabilization, also for planar‐biaxial loading.A modified COD strain range approach showed a good correlation in the LCF regime.Crack initiation occurred on the surface at oxidized primary carbides in the gauge area.The crack paths were monitored for the different planar‐biaxial loading conditions. [ABSTRACT FROM AUTHOR]

Much progress has been witnessed in exploring host–guest type ferroelectrics represented by ammonium‐crown ether compounds. However, the major obstacles in expanding their promising applications in nonvolatile memory elements, capacitors, and sensors are relatively low Curie temperature (Tc) and uniaxial attribute. Herein, by screening different organic cations and inorganic anions to assemble with 18‐crown‐6 molecule, it is found that a new ammonium‐crown ether inclusion ferroelectric 1, [(ATHTP)(18‐crown‐6)]BF4 (ATHTP = protonated 4‐aminotetrahydrothiopyran), undergoing a ferroelectric phase transition at a much higher Tc of 392 K which is comparable to BaTiO3 (Tc = 393 K). Notably, the distinct symmetry breaking, that is, 4/mmmFmm2, leads to a biaxial ferroelectric with four equivalent directions of polarization. Such high Tc and multiaxial nature are rare in existing crown ether‐based ferroelectrics. This work can help the exploration of high‐Tc multiaxial ferroelectrics toward further device applications. [ABSTRACT FROM AUTHOR]

Hematite carries magnetic signals of interest in tectonic, paleoclimatic, paleomagnetic, and planetary studies. First‐order reversal curve (FORC) diagrams have become an important tool for assessing the domain state of, and magnetostatic interactions among, magnetic particles in such studies. We present here FORC diagrams for diverse hematite samples, which provide a catalog for comparison with other studies and explain key features observed for hematite. Ridge‐type signatures typical of uniaxial single‐domain particle assemblages and "kidney‐shaped" FORC signatures, and combinations of these responses, occur commonly in natural and synthetic hematite. Asymmetric features that arise from the triaxial basal plane anisotropy of hematite contribute to vertical spreading in kidney‐shaped FORC distributions and are intrinsic responses even for magnetostatically noninteracting particles. The dominant FORC distribution type in a sample (ridge, kidney‐shaped, or mixture) depends on the balance between uniaxial/triaxial switching. The identified signals explain magnetization switching and anisotropy features that are intrinsic to the magnetic properties of hematite and other materials with multiaxial magnetic anisotropy. Plain Language Summary: First‐order reversal curve (FORC) diagrams have become a standard method for identifying the domain state of magnetic materials. It has recently been demonstrated that the magnetic anisotropy type can also be identified using FORC diagrams. The magnetic domain state and anisotropy type of a magnetic mineral control the fidelity of recording of magnetic information, so identifying these features is fundamental to paleomagnetic, rock magnetic, and environmental magnetic studies. Hematite is a naturally abundant magnetic mineral that is encountered commonly in such studies, so it is important to have extensive FORC reference data for this mineral. We present the most comprehensive available FORC study of diverse natural and synthetic hematite samples, including numerical simulation results, to seek to explain key domain state and anisotropy signals for hematite. Key Points: FORC diagrams are presented for diverse natural and synthetic hematite samples to demonstrate domain state and anisotropy signaturesKidney‐shaped FORC distributions are indicative of multiaxial anisotropy and central ridge‐type distributions reflect uniaxial anisotropyThe dominant FORC distribution type depends on the balance between uniaxial and triaxial switching mechanisms [ABSTRACT FROM AUTHOR]

The compressive strength of concrete under biaxial dynamic compression The compressive strength of two concretes under biaxial dynamic compressive stress was investigated. A biaxial split Hopkinson bar was used, that applied the dynamic load to the test specimen in the form of two load waves perpendicular to each other. For reference, the static compressive strengths under biaxial load with different stress ratios of the two load axes were determined in a triaxial testing machine. The results indicate a partially superposition of the two strength‐increasing effects of multi‐axial compressive stress and increased strain rate. In particular, clear differences can be seen in the fracture and crack pattern for the different load types. [ABSTRACT FROM AUTHOR]

Important components such as gears, rollers, or bearings operate in rolling‐sliding contact loading conditions. Determination of their fatigue lives remains a challenging task due to complex states of stress and strain in the contact region, as well as complex contact conditions such as variable loading amplitude and complex geometry of contact. A mathematical model of rolling‐sliding line contact combined with a multiaxial fatigue life calculation model based on the Fatemi‐Socie critical plane crack initiation criterion is proposed. The developed model was applied to gears' teeth in mesh and compared with fatigue lives of gears reported in the literature. Good agreement was determined confirming the validity of the proposed model. A further advantage is obtaining locations of initiated cracks and the orientation of critical plane(s), which can subsequently be used for the estimation of crack shapes in initial phases of their growth and the damage type that they can be expected to develop into. [ABSTRACT FROM AUTHOR]

The damage estimation for a structure under random loading is a challenge in fatigue assessment, especially when the loading is multiaxial. The comparison of the effect of different spectra on fatigue damage is essential when the structure can be subjected to different types of loadings. Therefore, in the present paper, the expected fatigue damage produced on metallic structures by combined bending and torsion stationary proportional and nonproportional loading is evaluated varying the shape of spectra of the normal and shear stress tensor components. [ABSTRACT FROM AUTHOR]

This paper presents an overview on the experimental investigation of the response of composite materials under multiaxial cyclic loading, starting from the pioneering works in the early 1970s to arrive to the research activities run in these days by the scientific community and concluding with the areas still open. The experimental techniques and sample geometries are compared, illustrating advantages and drawbacks of each solution, also with reference to the outcomes of the research. The influence of the main design parameters are illustrated, taking advantage of experimental results from the extensive investigation carried out in the last years at the University of Padova. Needs of future research are eventually addressed. [ABSTRACT FROM AUTHOR]

Calculations of creep damage under conditions of strain control are often carried out using either a time fraction approach or a ductility exhaustion approach. In practice, calculations of creep damage are further complicated by the presence of multiaxial states of stress. In the case of the time fraction approach, there are a number of models that can be used to predict the effect of state of stress on creep rupture strength. In particular, Huddleston developed a model from data on stainless steels. The R5 procedure uses a ductility exhaustion approach to calculate creep damage and includes a model for use under triaxial states of stress. The aim of this paper is to describe the development of this model, which is based on considerations of cavity nucleation and growth and was developed from multiaxial creep data on Type 304 and 316 steels. [ABSTRACT FROM AUTHOR]

Simulations of the nucleation of dislocations, glide and annihilation ahead of a fatigue crack growing along a localized slip band (a ‘long’ Stage I crack or a Stage II crack with a K value close to the threshold) are performed for the case of push–pull or reversed torsion loadings, ignoring, in a first approach, the effect of grain boundaries. The crack growth rates are deduced from the dislocation flux at the crack tip. An influence of the normal stress on the friction between the crack flanks as well as on the condition for dislocation emission is introduced. A slower Stage I growth rate is then predicted for reversed torsion, consistent with experimental data. [ABSTRACT FROM AUTHOR]