Research on pavement longitudinal crack propagation under non-uniform vehicle loading

The top-down crack (TDC) has become the major cracking mechanism in thick pavement structure, especially for the perpetual pavement. The heavy-vehicle load condition plays a key role in the fracture characteristics of pavement cracks. A three-dimensional finite element (FE) model of the tire tread rubber-block and the pavement is established to describe the stress–strain field of the pavement with TDC. The three-directional friction condition and non-uniform distribution between tire and pavement are especially considered. Then the orthogonal Design of Experiment method is applied to discuss the effect law of fracture characteristics for the longitudinal crack affected by the multiple loading parameters simultaneously. Based on the statistics and data analysis of the diverse test results, it is found there is a nonlinear relationship between the equivalent stress intensity factor of the pavement and the load parameters.The longitudinal distance (from the load location to the center of the crack port) has a great influence on the equivalent stress intensity factor. The equivalent stress intensity factor of the crack port is more than double the crack tip buried in pavement, which extends in II/III composite type mostly. The simulation results can be used as reference for the further study on the fracture mechanism of pavement cracks and their control technique.     

Augmented reality in informal learning environments: A field experiment in a mathematics exhibition

Recent advances in mobile technologies (esp., smartphones and tablets with built-in cameras, GPS and Internet access) made augmented reality (AR) applications available for the broad public. While many researchers have examined the affordances and constraints of AR for teaching and learning, quantitative evidence for its effectiveness is still scarce. To contribute to filling this research gap, we designed and conducted a pretest–posttest crossover field experiment with 101 participants at a mathematics exhibition to measure the effect of AR on acquiring and retaining mathematical knowledge in an informal learning environment. We hypothesized that visitors acquire more knowledge from augmented exhibits than from exhibits without AR. The theoretical rationale for our hypothesis is that AR allows for the efficient and effective implementation of a subset of the design principles defined in the cognitive theory of multimedia learning. The empirical results we obtained show that museum visitors performed significantly better on knowledge acquisition and retention tests related to augmented exhibits than to non-augmented exhibits and that they perceived AR as a valuable and desirable add-on for museum exhibitions.     

高压涡轮冷却外壳成形工艺及模具设计

分析了高压涡轮冷却外壳的成形工艺，并介绍了聚氨酯胀形模的结构设计和模具工作过程以及模具调试改进。     

Assessment of forming parameters influencing spring-back in multi-point forming process: A comprehensive experimental and numerical study

Like all sheet metal forming methods, one of the main characteristics of parts formed by multi-point forming is dimensional deviation caused by elastic recovery that is known as spring-back. In this paper the effects of material property, sheet thickness and anisotropy ratio along with process parameters such as elastic layer thickness, elastic layer hardness and number of punch elements on spring-back are studied utilizing finite element simulations and experimental tests. Experimental tests are carried out under various conditions by forming V-shaped and Sin-shaped geometries. Aluminum alloy 3105, stainless steel 304 and pure copper were used as sheet materials for experiments. Likewise, black rubber with shore A hardness of 50 and polyurethane with hardness of 65 and 85 were allocated as elastic layers. The Abaqus® commercial code is employed for finite element simulations. The definition of yield behavior of utilized sheet materials is fulfilled by using three yield criteria of Barlat-89, Hill-48 and Von-Mises. Since the Barlat-89 is not adopted in Abaqus, VUMAT and UMAT user defined subroutines are provided and integrated with explicit simulation of forming process and implicit simulation of spring-back phenomenon respectively. The results indicate that parameters such as material property, blank thickness and anisotropy affect spring-back in multi-point forming. Also the thickness and hardness of elastic layers are novel ideas that should be considered in order to minimize the spring-back. In general, using the elastic layer with minimum possible thickness and greater hardness beside the maximum number of pins leads to minimum spring-back.     

Comparing attack trees and misuse cases in an industrial setting

The last decade has seen an increasing focus on addressing security already during the earliest stages of system development, such as requirements determination. Attack trees and misuse cases are established techniques for representing security threats along with their potential mitigations. Previous work has compared attack trees and misuse cases in two experiments with students. The present paper instead presents an experiment where industrial practitioners perform the experimental tasks in their workplace. The industrial experiment confirms a central finding from the student experiments: that attack trees tend to help identifying more threats than misuse cases. It also presents a new result: that misuse cases tend to encourage identification of threats associated with earlier development stages than attack trees. The two techniques should therefore be considered complementary and should be used together in practical requirements work.     

响应面优化草石蚕多糖提取工艺研究

以草石蚕为原料，研究了草石蚕中多糖提取的工艺条件。在单因素试验基础上，通过响应面试验优化了草石蚕中多糖提取的工艺条件。结果表明，草石蚕中多糖的最佳提取工艺条件为：提取温度79．00℃，提取时间2．82h，乙醇体积浓度81．22％，料液比1g：18．49mL，此条件下草石蚕多糖提取率4．89％。     

Numerical simulation and design optimisation of an integrally-heated tool for composite manufacturing

Tooling design is crucial for the production of cost-effective and durable composite products. As part of the current search for cost reduction, integrally-heated tooling is one of the technologies available for ‘out-of-autoclave’ processing of advanced thermoset polymer composites. Despite their advantages, integrally-heated tools can suffer from uneven distribution of temperature, variability in heat flow rate and inconsistency in heating/cooling time. This research, therefore, investigates a number of design variables such as shape and layout of heating channels in order to improve the thermal performance of an integrally-heated tool. Design of Experiments (DoE) has been carried out using Taguchi’s Orthogonal Array (OA) method to set several combinations of design parameters. Each of these design combinations has been evaluated through numerical simulation to investigate heating time and mould surface temperature variation. The simulation results suggest that the layout of the channels and their separation play a vital role in the thermal performance. Signal-to-Noise (S/N) ratio and analysis of variance (ANOVA) have been applied to the results obtained to identify the optimal design combination of the integrally-heated tool. Statistical analysis reveals that the heating performance of an integrally-heated tool can be significantly improved when the channels’ layout is parallel. The shape of the channels has negligible effect and the distance between the channels should be determined based on the production requirement.     

汽车门框上条制件拉弯成形模具设计简

汽车门框、窗框多由各种复杂截面型材弯曲成形后焊接而成，型材截面复杂，并且形状多为空间三维曲面，该类复杂截面型材的高精度弯曲成形是制造汽车门框和窗框的关键技术。通过分析某汽车门框上条制件的成形工艺特点，综合比较各种弯曲方式后选取了张臂式拉弯成形工艺，并设计了拉弯成形模具、切断机构、冲孔及辅助成形装置，利用该模具可以成形出符合制件质量要求的车门框上条工件。     

Effect of material scatter on the plastic behavior and stretchability in sheet metal forming

Robust design of forming processes is gaining attention throughout the industry. To analyze the robustness of a sheet metal forming process using finite element (FE) simulations, an accurate input in terms of parameter scatter is required. This paper presents a pragmatic, accurate and economic approach for measuring and modeling one of the main inputs, i.e. material properties and its associated scattering.For the purpose of this research, samples of 41 coils of a forming steel DX54D+Z (EN 10327:2004) from multiple casts have been collected. Fully determining the stochastic material behavior to the required accuracy for modeling in FE simulations would require many mechanical experiments. Instead, the present work combines mechanical testing and texture analysis to limit the required effort. Moreover, use is made of the correlations between the material parameters to efficiently model the material property scatter for use in the numerical robustness analysis. The proposed approach is validated by the forming of a series of cup products using the collected material. The observed experimental scatter can be reproduced efficiently using FE simulations, demonstrating the potential of the modeling approach and robustness analysis in general.