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• The relationship between non-uniform deformation and residual stress was analyzed, and the fundamental equations of residual stress were established. • The concept of the "non-coordination coefficient" was introduced, revealing the physical mechanism behind residual stress caused by non-uniform deformation. • The appearance of residual stress is essentially to force the inconsistent deformation of various parts inside the object to maintain its integrity and continuity. • The difference in the severity of "penetrability" induced by different temperature gradients determines the difference in residual stress between rolled and quenched rings. • Under the same process conditions, 2219 Al-Cu alloy larger rings have higher and more non-uniform residual stress than smaller rings. The large-scale ring components, as thin-walled structures, are prone to unpredictable machining deformation due to the initial residual stresses introduced by rolling and quenching, which seriously affect the dimensional accuracy and service life of the ring components. Therefore, the relief and homogenization of residual stress inside large-scale ring components is crucial. However, the existing studies rarely involve the essential causes and the evolution laws of residual stresses during the manufacturing of ring components, which are indispensable for understanding the failure mechanisms of components caused by residual stresses and specifying relevant protective measures. Therefore, the evolution and distribution laws of stress-microstructure-property non-uniformity during the hot forming (ring rolling) and heat treatment (quenching) of 2219 Al-Cu alloy rings were precisely and deeply explored using scaled experiments in this paper. The relationship between non-uniform deformation and residual stresses was analyzed, and the basic equation that residual stresses must satisfy was established. Furthermore, the concept of the "non-coordination coefficient" was proposed, revealing the physical mechanism of residual stresses induced by non-uniform deformation. In addition, the influencing factors and formation mechanisms of residual stresses in the rolled and quenched state of rings were studied, and the essential reasons for the differences in residual stresses between the rolling and quenching processes were obtained. The experimental results indicate that the circumferential and axial residual stresses increased from 1.48 and 0.51 MPa to −142.68 and −122.31 MPa, respectively. The standard deviation changed from 13.47 and 33.52 MPa to 63.42 and 61.61 MPa, respectively. The maximum range of tensile strength, yield strength and elongation rates of the rolling and quenched state is 12.82 and 20.16 MPa, 17.49 and 22.14 MPa, and 8.62 % and 7.56 %, respectively. All fractures are microporous aggregation ductile, including dimple transgranular fracture and intergranular fracture. The quenched state exhibits a significantly larger grain size compared to the rolled state. The appearance of residual stress is essentially to force the inconsistent deformation of various parts inside the object to maintain its integrity and continuity, which leads to a local mismatch of micro-elements inside the ring and further induces non-uniform strain and stress. The difference in the severity of "penetrability" induced by different temperature gradients determines the difference in residual stress between rolled and quenched rings, larger rings have higher and more non-uniform residual stress than smaller rings under the same process conditions. The above results deepen the theoretical understanding of residual stress formation mechanisms and lay a theoretical foundation for the comprehensive evaluation of performance degradation and service failure analysis of large ring components. [ABSTRACT FROM AUTHOR]

This article proposes a consistent and general approach to train physics-augmented neural networks with observable data to enrich and represent nonlinear history-dependent material behaviors in terms of both state equations and evolution laws. In this learning strategy consistent with thermodynamics, the constitutive model is expressed using two potentials (free energy and dissipation potential) which are represented by input-convex neural networks, thus automatically satisfying the principles of thermodynamics. The neural network is trained thanks to an unsupervised procedure that does not rely on strain–stress pairs but needs only partial strain or displacement measurements inside the structure, moreover with uncertain boundary conditions. This method is based on the minimization of the modified Constitutive Relation Error functional, and it extends previous works on this error measure for neural networks to the case of history-dependent behaviors, which requires to design a specific minimization procedure. Given that neural networks for typical structural health monitoring applications often need to be trained online, there is here a significant emphasis placed on automatically and adaptively tuning crucial hyperparameters such as learning rate or weighting between losses. The method is evaluated on elastoplastic and elastoviscoplastic test cases with synthetic data collected from optic fiber or full-field measurements. It is shown that the method can properly learn hidden behaviors, achieves high robustness to noise level, and low sensitivity to user-defined hyperparameters. • A consistent hybrid approach is proposed to learn complex history-dependent constitutive laws. • The unsupervised learning integrates a performance criterion related to modeling error. • An automatic adaptive tuning of hyper-parameters is derived within this strategy. • A specific algorithm is introduced to tackle admissibility constraints and nonlinearities. • The interest and robustness of the approach are validated on several nonlinear constitutive laws. [ABSTRACT FROM AUTHOR]

A new method for calculating the parameters of the hypoid pitch cone, which simplifies the calculation process, is proposed. The method can easily obtain the evolution laws of hypoid pitch cones. The evolution limits of the hypoid pitch cone can be obtained by calculation. The pinion pitch cone evolves from cylinder to cone, and the gear pitch cone evolves from plane to cylinder. In the evolution process, all pitch cones can meet the preset values of key parameters. The variation law of the values representing lubrication and contact characteristics on the whole tooth surface during the evolution of pitch cone is studied. • A single equation containing relationships determines the tangent cones is found. • The feasible region of the hypoid gear pitch cone is found. • The evolution process of the pitch cone is studied in the feasible region. • The characteristics evolution laws on the tooth surface are found. [ABSTRACT FROM AUTHOR]

In this study, a visualizable experimental platform of steam ejector oriented towards MED-TVC desalination system is constructed, and the evolution laws of two-phase choking flow and ejector's entrainment performance under various operating parameters are obtained. Further, a matching double-choking theory with consideration of the condensing flow is developed to explain the inherent reason behind these evolution laws. Key results revealed that the formed two-phase choking flows have great effects on ejector's entrainment performance. The primary jet flow choking area linearly increases as the primary steam pressure raises, and the entrainment choking area experiences a small reduction, while the extended flow area marginally increases. Accordingly, the entrainment ratio significantly decreases, while the choking cross-section is slightly shifted upstream. In addition, the primary jet flow choking area considerably decreases with increasing entrainment pressure, but the entrainment choking area is nearly unchanged and the extended flow area increases by more than 8 times. As a result, the entrainment ratio remarkably increases, the choking cross-section migration distances are much larger than that in the case of primary steam pressure varies. A meaningful guide evolves from fact that priority should be given to restrain the condensing flow for achieving a higher energy efficiency of ejector. • Two-phase choking flow regimes inside the steam ejector are visualized and analyzed. • Evolution laws of ejector's choking flow and entrainment performance are obtained. • An improved double-choking theory is developed to explain these evolution laws. • Essential relation between choking flow and entrainment performance is established. • Adverse effects of the two-phase choking flow on ejector performance are discussed. [ABSTRACT FROM AUTHOR]

The aim of this paper is to develop a thermodynamically consistent micromechanical concept for the damage analysis of viscoelastic and quasi-brittle materials. As kinematical damage variables a set of scalar-, vector-, and tensor-valued functions is chosen to describe isotropic and anisotropic damage. Since the process of material degradation is governed by physical mechanisms on levels with different length scale, the macro- and mesolevel, where on the mesolevel microdefects evolve due to microforces, we formulate in this paper the dynamical balance laws for macro- and microforces and the first and second law of thermodynamics for macro- and mesolevel.Assuming a general form of the constitutive equations for thermo-viscoelastic and quasi-brittle materials, it is shown that according to the restrictions imposed by the Clausius–Duhem inequality macro- and microforces consist of two parts, a non-dissipative and a dissipative part, where on the mesolevel the latter can be regarded as driving forces on moving microdefects. It is shown that the non-dissipative forces can be derived from a free energy potential and the dissipative forces from a dissipation pseudo-potential, if its existence can be assured.The micromechanical damage theory presented in this paper can be considered as a framework which enables the formulation of various weakly nonlocal and gradient, respectively, damage models. This is outlined in detail for isotropic and anisotropic damage. [Copyright &y& Elsevier]

Recently, bionic thin-walled structures have attracted widespread attention in automotive safety design because of their excellent crashworthiness behavior and weight efficiency. In this paper, inspired by the evolution laws and microstructure of plant stems, a group of bionic tubes with m parts and n layers (PmLnBTs) are proposed and investigated by theoretical prediction and numerical analysis. Theoretical models of PmLnBTs are developed to predict the specific energy absorption. Finite element model is conducted with LS-DYNA and validated by a quasi-static axial crushing experiment. The accuracy of the theoretical model is verified by numerical analysis, and the maximum relative error is less than 7%. Furthermore, parametric studies are conducted to investigate the effects of geometric parameters on the energy absorption capability of PmLnBTs. The results indicate that the PmLnBTs exhibit superior crashworthiness performance compared to traditional bi-tubular circle tubes. Moreover, when designing such a bionic energy absorber, it can effectively improve the crashworthiness performance by appropriately increasing the number of layers, reducing the outermost circle diameter or avoiding innermost circle diameter value too large or too small. The findings of this paper provide a guidance for the design of energy absorber with excellent energy absorption performance. Image 1 • Inspired by the evolution laws and microstructure of plant steams, a group of bionic tubes namedPmLnBTs were proposed. • A theoretical model of PmLnBTs was established and validated to predict the energy absorption capability of PmLnBTs. • The PmLnBTs exhibit significant crashworthiness advantages than traditional bi-tubular circle tube (TBCT) with same mass. • The number of layers n and innermost circle diameter d have a significant effect on the crashworthiness of PmLnBTs. [ABSTRACT FROM AUTHOR]

• A double-choking theory is proposed. • A quantitative analysis of the entrainment choking flow has achieved. • The inherent reason behind the evolution law of ejector performance is illuminated. • The fundamental link between entrainment performance and choking flow is revealed. • The evolution laws under various operational and geometry parameters have explained. There are few systematic studies to investigate the inherent reason behind the evolution law of ejector performance, only some simple qualitative or roundabout analysis. In this paper, a double-choking theory is proposed to provide an in-depth explanation of the evolution laws of ejector performance. The systematic investigation and quantitative analysis focus on the influences of various operational and geometrical parameters on the ejector choking flows. Key results revealed that the flow area of the primary jet flow at the choking cross-section A py almost linearly increases with higher primary flow pressure p p0 , while the entrainment choking area A ey declines instead, and thus the entrainment ratio ε decreases. The mixing pressure p y significantly increases with entrainment pressure p e0 , and A py partly reduces. Consequently, A ey becomes larger and ε is accordingly with an over-double increase. A py undergoes a continuous decrease when the area ratio of primary nozzle λ t increases, and thus ε rises consistently although A ey1 eventually experiences a slight decrease. However, the choking state of the entrained flow would discontinue as λ t exceeds its critical value λ tc. Additionally, A ey increases substantially when the area ratio of the constant-area section λ 3 enlarges, while A py and p y always remain unchanged. Accordingly, ε follows the same increasing trajectory as A ey. These impactful results could serve as an essential guide for optimizing the ejector design, and also ensure a clearer perspective to understand the fundamental link between the ejector's entrainment performance and choking flow. [ABSTRACT FROM AUTHOR]