The 7th International Conference on Material Strength and Applied Mechanics
(MSAM 2024)

Abstract: Fatigue damage is usually defined as ∑n_i / N_i , i.e., the sum of the ratios of stress cycle number to fatigue life under different stress levels. When fatigue life needs to be treated as a random variable, such definition will result in complex cumulative damage calculation. Besides, different definition on fatigue damage implies different critical damage for fatigue failure criterion. This paper defines and discusses different fatigue damage definitions and corresponding issues about failure probability prediction under variable amplitude stress histories. It shows that in the situation of fatigue life following the three-parameter Weibull distribution, the fatigue damage defined based on the location parameter, i.e., the threshold of the random life, is appropriate for cumulative fatigue damage calculation and probabilistic fatigue life prediction.

Keywords: Fatigue damage, critical damage, fatigue life, Weibull distribution, failure probability.

Abstract: To be updated

Abstract: As one of the principals supporting platforms and key technologies of the "Materials Genome Initiative", high-throughput experimental technology has drastically transformed the landscape of material development by substantially reducing both the development time and associated costs. One area where this impact is particularly evident is in the development of materials for aeroengines and gas turbine blades, where creep testing is a vital component of the development process. Traditionally, tensile creep testing methods have been utilised, but these are both time-consuming and expensive. In response to this challenge, this study introduces a novel approach of a rapid compression creep technique. This innovative method facilitates simultaneous testing of eight samples, thus significantly reducing the time and cost compared to traditional methods. Crucially, this study has successfully utilized the compression creep data to establish a quantitative correlation with tensile creep data, leading to accurate predictions of stress rupture life. Furthermore, this new testing method can also be employed for the rapid screening of creep properties during the development of new materials, allowing for a swift determination of creep stress exponents. This technique also offers the capability to screen the chemical composition of engineering materials. Thus, the rapid compression creep technique represents a significant advance in the field, offering a new method for the rapid evaluation of high-temperature performance in superalloys.

Keywords: High-throughput experimental technology, compressive and tensile creep, evaluation of creep behavior.

Abstract: Flexible and transparent antimicrobial touch/tactile sensors have received considerable attention on account of their wider applicability in personal electronic devices. For electronic devices, coated films should have an enough mechanical strength because of many touches in the case of smart phone applications. Herein, SZO-PTFE and ZnO-PTFE composite thin films with sensorial capabilities and high mechanical strengths are developed via a co-sputtering technique. Mechanical strengths of the composite films were investigated via micro-indenter. Their mechanical strengths showed similar results to that of the glass substrate. Elastic modulus and hardness of the ZnO-PTFE composite films showed almost 90 GPa (that of glass: 70 GPa) and 5.5 GPa (that of glass: 6.1 GPa), respectively. They showed a good adhesion between composite films and glass substrate via adhesive tape test. Furthermore, the linear response of the TENG to driven pressure indicates its excellent pressure-sensing ability, with an unprecedented sensitivity of 75.31 V/kPa and a touch sensitivity of 31.36 V/kPa. Further, the real-time application of ZnO-PTFE as display coating and self-powered touch sensor is demonstrated. This work demonstrates a simple route towards the design of smart coatings with high mechanical strengths.

Abstract: Since the beginning of the structural optimization field, the optimal design was characterized by the least-weight configuration. In this sense, all the researchers agreed on adopting the minimum-weight optimization statement as the most promising approach to achieve an optimized employment of material. However, especially for steel structures, this approach completely fails the primary goal of encouraging standardization of pieces during the production phase and reducing constructability issues at the assembly and erection phase. Except for rare cases, increasing diversity among structural elements (i.e. different lengths, different cross-sections and/or materials) leads to a dramatic increase in the financial cost as well as the environmental impact of the structure because of the material waste generated during the cutting procedure.

In this research, a Genetic Algorithm (GA) has been developed and the well-known one-dimensional bin packing problem (BPP) has been implemented within the structural optimization process. The Objective Function formulation lies in a marked change of the paradigm in which the target function is represented by the amount of steel required by the factory instead of the structural cost (e.g. weight). The proposed approach is tested on different steel structures with an increasing number of pieces moving from 2D truss beams to 3D domes. The best design is obtained by varying the size and the overall layout ensuring optimal stock of existing elements.

Finally, comparisons between the traditional minimum-weight approach and the proposed one have been provided for each case study, and economic and environmental benefits deriving from the latter have been discussed.

Abstract: Wear is a key factor that significantly limits the survival of total knee arthroplasties (TKAs). While it is known that this phenomenon is influenced by the applied load and the kinematic conditions between the prosthesis parts, it is unknown how the geometry of the TKA react on wear. This article has investigated, by means of multibody models, how different TKA sizes and TKA-related geometric parameters affect wear during gait motion. It has been demonstrated that wear rate increases, closely linearly, as a function of TKAs size, while the influence of TKA-related geometric parameters on wear propagation can be described by either linear or quadratic functions. These results, together with the newly introduced dimensionless parameters, demonstrate that the wear rate of TKAs can be reduced by choosing the right dimensions.

Abstract: The hot forged Ti-6Al-4V alloy demonstrates well constructured microstructure and balanced mechanical properties, which promotes its widely application in aviation field. However, its relative poor resistance to wear and foreign object impact usually leads to the cumulative damage, causing sudden failure and serious accident. Though the conventional coating technology could improve the surface damage resistance, the interface always becomes the origin of failure. Comparatively, Laser shock peening (LSP) has attracted significant interest, due to its controlled processing accuracy and great surface plastic deformation capability, which could form gradient grain structure with the gradient strengthening effect. Nevertheless, the specific mechanism of microstructure evolution and mechanical properties enhancement of LSP processed hot forged Ti-6Al-4V alloy is still obscure. In present research, the hot forged Ti-6Al-4V alloy was processed by LSP to regulate its superficial microstructure and improve mechanical properties, helping to understand the inner mechansim. The results reveal that LSP could simultaneously result in the merging of ultra-fine α-Ti grains and refinement of coarse α-Ti grains, which reconstruct the dual-size grain structure. The crystal tilting and transformation promoted by the generation and movement of dislocations benefit the merging of ultra-fine grains. Due to the different slip systems in dual phases, β-Ti phases exhibit much greater response to slip under surface plastic deformation, which are enforced to deform and construct the shell structure by sliding and phase transformation, while the α-Ti phases act as the core to synergistically construct ‘core-shell’ like structure. The increase of LSP number promotes the well wrapping of the ‘core-shell’ like structure and strengthens it by abundant dislocations, which also forms the gradient grain structure from surface to inner. Since the microstructure regulation and crystal defects engineering, the LSP improves the surface damage resistance and mechanical properties of the hot forged Ti-6Al-4V alloy obviously, which indicates a new method to increase properties of the hot forged Ti-6Al-4V alloy component further.

Keywords: Ti-6Al-4V alloy, laser shock peening, microstructure, core-shell structure, wear properties, tensile properties.

Acknowledgements: This work was supported by the Shenzhen Basic Research Project (JCYJ20210324120001003 and JCYJ20200109144608205).

Abstract: Lithium-metal batteries (LMBs) are promising energy storage devices due to the high capacity and minimum negative electrochemical potential. Nevertheless, their concrete applications remain disturbed by unbalanced electrolyte-electrode interfaces, limited electrochemical window, and high-risk. Herein, a novel strategy to obtain dual ceramic-based electrolytes that possess great potential in energy storage due to their higher level of energy densities in LMBs. Electrolyte film developed via the curable system, aimed to prepare flexible Li⁺ interpenetrating network film to integrate the two ceramic structures with polyethylene oxide to yield the free-standing electrolytes film for better battery safety and desired interfacial stability. The films presented a satisfactory electrochemical performance, including, good ionic conductivity, large transference number, and wide electrochemical stability window (ESW) at room temperature. Most importantly, the fundamental function of fillers is to support building a stable solid-electrolyte-interphase (SEI) and limits the growth of dendrites. Thus, prepared dual ceramic-based electrolytes effectively renders to inhibit lithium dendrite growth in a symmetrical cell test during charge/discharge at a current density of 2 mA/cm² and 0.25 mA/cm² above 2000 h without short-circuiting occurrence at room temperature. Besides, the battery assembled of exhibits superior cyclic stability with high columbic efficiency. This research recommends that the binary network structures of Li-ion conductor help to design a prime solution of promising electrolyte for high-performance LMBs applications.

Keywords: Electrolytes, PEO, PVP, lithium-metal batteries, Li-dendrites.

Abstract: High thermal-dimensional stability is crucial for high-precision applications, e.g., unmanned monitoring of Moon surface environment, etc. This study designs a novel 3D carbon fibre reinforced plastic (CFRP) composite lattice with high thermal-dimensional stability. First, the planar CFRP composite lattice was designed with a continuous carbon fibre reinforced polyamide (PA) central cross-lattice interlocked with four short carbon fibre reinforced PA outer-strips, fabricated via fused filament fabrication. Second, a novel three-dimensional (3D) composite lattice structure was developed and calculated, exhibiting a negative effective CTE at −0.18×10⁻⁶/℃, based on the planar composite lattices. Third, lightweight optimisation was conducted for high thermal-dimensional-stability.

Keywords: Continuous carbon fibre, finite element analysis, coefficient of thermal expansion, FFF, thermal-dimensional stability.