Fatigue Life Assessment of Tower Crane Based on Neural Network to Obtain Stress Spectrum

In order to reduce the probability of crane safety accidents, a method based on radial basis neural network is proposed to quickly obtain the stress spectrum and calculate the remaining life of the crane. Firstly, taking an in-service tower crane as an example, an ANSYS finite element model is established based on actual parameters, and the finite element model is statically analyzed to obtain the location of the dangerous point. Secondly, the typical operating conditions of the crane are simulated. The position of the trolley and the lifting load are used as the input layer while the equivalent stress value at any point is used as the output layer to train the radial basis neural network model. Using the trained radial basis neural network model can obtain time-stress curve at any point quickly. Finally the remaining life is assessed based on the fracture mechanics method. The results show that this method that using the radial basis function neural network model to obtain the time-stress curve at any point can greatly save the cumbersome process and a lot of investment in the field measurement of the crane, and also provides a reliable basis for the long-term safe use and later maintenance of the crane.

Study of Allowable Interlaminar Normal Stress Based on the Time–Temperature Equivalence Principle in Automated Fiber Placement Process

Automatic fiber placement (AFP) is a type of labor-saving automatic technology for forming composite materials that are widely used in aviation and other fields. In this process, concave surface delamination is a common defect, as existing research on the conditions for this defect to occur is insufficient. To predict the occurrence of this defect, the concept of allowable interlaminar normal stress is proposed to define its occurrence conditions, and based on this concept, probe tests are carried out using the principle of time–temperature equivalence. Through the laying speed/allowable normal stress curve measured in the probe experiment, the physical meaning of allowable normal stress is discussed. At the same time, the measured curve is quantitatively analyzed, combined with viscoelastic theory and the molecular diffusion reptation model, and the dominating effect in the formation of a metal/prepreg layer and prepreg/prepreg layer is determined. Finally, the experimental data are used to guide the parameter selection in an automatic placement engineering case and prove its correctness.

A comparison between constitutive models for the municipal solid waste

This paper compares the behavioural models of municipal solid waste (MSW) using the corresponding experimental data. To do so, the proposed models are first reviewed and, then, the algorithms and codes of different models are written. After obtaining each model’s algorithm, the same experimental data are considered as input, and the strain–stress curve is plotted for each model. In the first method, the total strain in the waste is obtained based on the summation of the elastic, plastic, biological, and creep strains. Afterward, the equivalent stress is obtained. In this method, using biological changes over time, the age of the waste is calculated as an effective parameter in MSW behaviour. Moreover, the effect of creep on the waste is considered independently. In the second algorithm, MSW is considered as fibre and paste material, and the strain–stress curve is obtained. In this method, the waste is considered as a soil model, and the effect of different parameters are calculated. Due to the complexity of the MSW behaviour and considering various parameters, such as the age of the waste, E changes over time, creep, and biological changes, the Krase model has less error than the other models. Using the soil behaviour model for the waste has a significant error, indicating the difference between the results for the behaviours of the two substances.

Fatigue Property of Welded T-Shaped Joints Using the Structural Stress Method

Various types of welded joints are of wide application in industrial and productional regions, including T-shaped, butt, and fillet joints of steel, stainless steel, and cast steel. Under cyclic fatigue load, the fatigue performance of welded joints is significant for the engineering design and it’s of interest to investigate the fatigue property of the welded joints using the recommended prediction methods. In this paper, the fatigue performance of welded T-shaped joints is investigated. The mesh-insensitive property of the structural stress method is validated with the comparison of various prediction methods. The fatigue cyclic life of welded T-shaped joints under tensile loads is analyzed. The structural stress curve of T-shaped joints with various base metal thicknesses is determined for the engineering design.

The identification of strain-stress curve for 5049 aluminum based on tube hydraulic bulging test

Tube hydraulic bulging tests with fixed-end conditions are carried out to explore tubular material characteristics for 5049 aluminium. Tube diameter at the center of specimen and pole thickness under different internal pressures are recorded during forming process. Based on experimental data, two types of theoretical models using membrane mechanics and total strain theory are applied to determine the flow stress curve of tubular specimens. A tension specimen is cut from the same tube along longitudinal direction and strain-stress curve is fitted by a universal tensile test. In order to test their accuracy, obtained material parameters from three methods are imported into a finite element model (FEM) and its predicted results are compared with bugle height measured from experiments. The comparison shows that the flow stress curve of 5049 aluminium tube can be identified by these three methods and simulated results from total strain model has a better agreement with experimental measures compared with the other two methods.

Process Signature for Laser Hardening

During many manufacturing processes for surface treatment of steel components heat will be exchanged between the environment and the workpiece. The heat exchange commonly leads to temperature gradients within the surface near area of the workpiece, which involve mechanical strains inside the material. If the corresponding stresses exceed locally the yield strength of the material residual stresses can remain after the process. If the temperature increase is high enough additionally phase transformation to austenite occurs and may lead further on due to a fast cooling to the very hard phase martensite. This investigation focuses on the correlation between concrete thermal loads such as temperature and temperature gradients and resulting modifications such as changes of the residual stress, the microstructure, and the hardness respectively. Within this consideration the thermal loads are the causes of the modifications and will be called internal material loads. The correlations between the generated internal material loads and the material modifications will be called Process Signature. The idea is that Process Signatures provide the possibility to engineer the workpiece surface layer and its functional properties in a knowledge-based way. This contribution presents some Process Signature components for a thermally dominated process with phase transformation: laser hardening. The target quantities of the modifications are the change of the residual stress state at the surface and the position of the 1st zero-crossing of the residual stress curve. Based on Finite Element simulations the internal thermal loadings during laser hardening are considered. The investigations identify for the considered target quantities the maximal temperature, the maximal temperature gradient, and the heating time as important parameters of the thermal loads.

Numerical Analysis of the Welding Behaviors in Micro-Copper Bumps

In this study, three-dimensional simulations of the ultrasonic vibration bonding process of micro-copper blocks were conducted using the finite element method. We analyzed the effects of ultrasonic vibration frequency on the stress field, strain field, and temperature field at the copper bump joint surface. The results showed that the bonding process is successfully simulated at room temperature. The stress curve of the bonding process could be divided into three stages: stress rising stage, stress falling stage, and stress stabilization stage. Moreover, it was found that the end of the curve exhibited characteristics of a solid solution phase at higher frequencies. It is hypothesized that the high-density dislocations formed at this stage may result in conveyance channels that facilitate the atomic diffusion at the contact surface. The simulation results indicated that copper micro-bump bonding occurs at an ultrasonic frequency of 50 kHz or higher.

Investigation of fiber slippage in the chopping process of carbon fiber tows under rigid support

As an important application form of carbon fiber (CF), short CFs and their production process have self-evident research value. In this work, the chopping process of CF tows under rigid support and the essential cause of high cutting forces were explored. Large-tow CFs containing 1–3000 single filaments were chopped, and the fracture processes were observed and described. It was found that obvious fiber slippage phenomena and intermediate fracture behaviors occurred during the chopping process. These factors not only increased the cutting force but also caused an uneven distribution of the cutting force along the width. A mechanical model was established to explain the fiber slippage and intermediate fracture. Based on material mechanics and analytical mechanics, the real process of fiber slippage and intermediate fracture was described by Hamilton’s principle. Moreover, a width constraint experiment was designed to indirectly verify fiber slippage phenomena and intermediate fracture behaviors. Through the analysis of the stress curve, it was proven that a reasonable width constraint could effectively limit fiber slippage and improve the uniformity of the distribution of the cutting force along the width of the tool, thus reducing the cutting force. This work can be used as an excellent guide for the chopping process in CF production.

Methods for measuring friction-independent flow stress curve to large strains using hyperbolic shaped compression specimen

The accurate measurement of flow stress curve to large strains using cylindrical compression specimen is always a great challenge due to the influence of friction. Recently, the present authors designed a hyperbolic shaped compression (HSC) specimen which can yield an average true stress- strain curve independent of friction and proposed a stress correction function for fast estimation of flow stress curve to large strains. The aim of this paper is threefold. Firstly, to investigate whether the analytical method for stress correction of tensile necking can, or cannot, be extended to HSC specimen for correcting average true stress into flow stress. Secondly, to develop an inverse method based on Kriging surrogate model for identifying the optimal parameters of modified Voce model using HSC specimen. Lastly, the advantages and disadvantages of these three methods were compared and the recommendations for application were also discussed. The results show that the analytical method is more suitable to the stress correction for material with higher n-value but shows worse capability for correcting flow stress related to large strains for material with lower n-value. For Q420 steel, the maximum strain achieved by HSC specimen (0.8) is far higher than that achieved by cylindrical tension specimen (0.55). The analytical method can correct the flow stress in the strain range of 0–0.5 effectively but underestimating the flow stress in the strain range of 0.5–0.8 due to its low n-value. Both inverse method and stress correction function can determine the flow stress in the strain range of 0–0.8 successfully. Thus, for isotropic material with tension–compression yield symmetry, it is recommended to use the HSC specimen instead of conventional tension and compression tests of cylindrical specimens to determine the flow stress curve to large strains.

Helmet chinstrap protective role in maxillofacial blast injury

BACKGROUND: The protective role of helmet accessories in moderating stress load generated by explosion shock waves of explosive devices is usually neglected. OBJECTIVE: In the presented study, the protective role of the helmet chinstrap against the impulse and overpressure experienced by the maxillofacial region were examined. METHODS: The explosion shock wave and skull interaction were investigated under three different configurations: (1) unprotected skull, (2) skull with helmet (3) skull with helmet and chinstrap. For this purpose, a 3D finite element model (FEM) was constructed to mimic the investigated biomechanics module. Three working conditions were set according to different explosive charges and distances to represent different load conditions. Case 1: 500 mg explosive trinitrotoluene (TNT), 3 cm, case 2: 1000 mg TNT, 3 cm, and case 3: 1000 mg TNT and 6 cm distance to the studied object. The explosion effect was discussed by examining the shock wave stress flow pattern. Three points were selected on the skull and the stress curve of each point position were illustrated for each case study. RESULTS: The results showed that the helmet chinstrap can reduce the explosive injuries and plays a protective role in the maxillofacial region, especially for the mandible.