Key Engineering Materials Vols. 525-526

Abstract: Laser cladding act as a remanufacturing technology used more and more but the study of the fatigue properties of such products falls relatively behind. To work out the influence fatigue damage and thermal damage have on the fatigue life of laser cladding remanufactured products, this paper deals with the study of the characteristic of metal magnetic memory (MMM) signals of components experienced with fatigue test and a succeeding laser surface burning. The MMM signals was acquired for three times, that is before fatigue test, after fatigue and after laser treatment, respectively. Statistic investigation of the experiment result showed that the magnetic signal was closely related to the state of fatigue damage and thermal damage of the specimen. Based on such result, it is expected to quantify the study by statistical analysis of large samples so as to find a correlationship with the last fatigue life.

Abstract: Corrosion fatigue is a form of degradation subjected to combined damage of mechanical stress and corrosive medium, which is an issue in aircraft industry. Experimental investigations on prior corrosion fatigue cracking behavior of LY12CZ were conducted with scanning electron microscope (SEM). Results indicate corrosion damage is important for the fatigue small cracking behavior of LY12CZ aluminum alloy. The effect of corrosion pit on fatigue crack can be characterized by the depth of corrosion pit. Based on small crack, another way to evaluate crack growth rate for AALY12CZ is proposed.

Abstract: In order to solve the problem how to calculate the stress intensity factor for a cracked flattened Brazilian disk under mode I loading, the finite element method was employed to analyze the stress intensity factor for the cracked flattened Brazilian disk under mode I loading, based on the closed-form expression of the stress intensity factor for a cracked Brazilian disk subjected to pressure. The analyzed result shows that within the certain range of the load distribution angle, the formula of the stress intensity factor for the cracked Brazilian disk can be directly used to calculate the stress intensity factor for the cracked flattened Brazilian disk under mode I loading.

Abstract: This paper presents a new method to conveniently calculate the stress intensity factors for the cracked flattened Brazilian disks under mixed-mode loading. The finite-element method is employed to confirm an assumption that the formula of the stress intensity factors for the cracked Brazilian disk subjected to pressure can be directly used to calculate the stress intensity factors for the cracked flattened Brazilian disk. The calculated results show that the assumption is valid and reliable. The calculated results also confirm that the Saint-Venant’s principle is still valid in fracture mechanics. In addition, the present paper proposes a concept of optimum load distribution angle.

Abstract: A super wedge tip element for application to a bi-material wedge is develop utilizing the thermo-mechanical stress and displacement field solutions in which the singular parts are numerical solutions. Singular stresses near apex of an arbitrary bi-material wedge under mechanical and thermal loading can be obtained from the coupling between the super wedge tip element and conventional finite elements. The validity of this novel finite element method is established through existing asymptotic solutions and conventional detailed finite element analysis.

Abstract: The spall fracture is a shock wave induced dynamic fracture phenomenon, it’s difficult to capture the features of the spall fracture when traditional finite element method based on continuum mechanics is applied. In this paper, a new and flexible meshless method, material point method, is used to study the spall fracture of metal material in the case of hypervelocity impact. Firstly, a computational process is given in which Johnson-cook plasticity model, Mie-Grüneisen equation of state and several failure models including hydrodynamic tensile failure model, effective plastic strain model and Johnson-cook failure model are considered. Then a 3D simulation of spall fracture of an armco iron target under impact loads by a 2024-T351aluminum projectile is carried out. At last, the numerical results show that the material point method can accurately capture important features of spall fracture such as the arrival times, magnitudes and shapes of both the compressive waves and tensile reflections in the spall region, and it’s proven that material point method is suitable to simulate the spall fracture in engineering applications.

Abstract: in this paper, the asymptotic expression of the buckling critical load coefficient of the thin cylindrical shell with local axial symmetry initial defects under the axial loads is deduced by used the Karman-Donnel Equation. The buckling safety margin equation of the cylindrical shell with initial defects is constructed. Furthermore, the buckling reliability index is solved by used AFOSM (Advanced First-Order Second Moment) method. In the end, a numerical example is given to analyze the influence of the band width and amplitude of local axial symmetry initial defects on the structural buckling reliability index.

Abstract: The residual stress distributions of 7075 aluminum alloy rectangular thick plates after quench-hardening had been simulated firstly, then all the results were presented and compared with each other. Some deep theoretical analyses were also carried out. The results show that complicated residual stress distribution regularities in aluminum alloy thick plates can be obtained by the finite element analysis successfully.

Abstract: Underwater explosive load calculation and numerical simulation is the key issues of the design of underwater conventional weapons and protection of ships and submarine. Underwater explosion involves strong nonliner problems and multi-material coupling problems. The method of underwater explosion calculation base on the material point method (MPM) is presented. The MPM takes the advantages of the both Euler and Lagrangian methods and overcomes the shortcomings of them. The problems in the underwater explosive simulation such as large deformation, moving material interfaces and deformable boundaries can be solved effectively by the MPM. At last, blast wave produced by TNT exploding under similar infinite water region is computed. The calculated results are in good agreement with the results of empirical formula of Cole and SPH. The simulation results show that the MPM is an effective tool for underwater explosion calculation.

Abstract: In this study, based on Goodman stress correction algorithm, four point bending fatigue behavior of brazed steel honeycomb sandwich panels at room temperature is simulated using Fe-safe emulation module. The cyclic load was sinusoidal with a frequency f= 10 Hz. The residual life and security coefficient are given in the condition of design fatigue lifetime of 10⁶ cycles. The results show that, in the local deformation, local maximum deformation occurs in the core wall under the load region, indicate that this region is the failure region of fatigue. And the residual life of the core wall in this region is less because of local stress concentration, the probability of failure becomes high, while the residual life in the region far away from the mid-span is high.