Commercially pure titanium (CP-Ti) has received a great deal of attention in medical applications. Improvement of its mechanical properties plays a key role in enhancing the biomechanical compatibility of Ti implants, leading to avoid revision surgeries. Emerging advanced manufacturing technologies such as selective laser melting (SLM) is providing an ideal platform for producing components with almost no geometric constraints and is economically feasible down to a batch size of one. This study presents the results of using SLM to produce CP-Ti parts starting from powder with a wide grain size range up to 100 μm. Accurate manipulation of SLM manufacturing parameters were applied to produce nearly full dense (>99.5%) CP-Ti parts without any post-treatments. Compared with the properties of those manufactured by traditional processing technologies, the microhardness, compressive, and tensile strengths of SLM-processed CP-Ti parts have been improved to 261 Hv, 1136 MPa, and 757 MPa, respectively, due to the formation of refined martensitic α′ grains during SLM. The optimal manufacturing parameters could enhance the strength and hardness of CP-Ti and yet maintaining the ductility of titanium. Fractography study of the tensile-failed SLM-processed specimens showed that incompletely melted particles and porosities caused early fracture in porous sample. Mixture of dimples and minor quasi-cleavage facets covered most fracture surface of full dense sample.

Manufacture by selective laser melting and mechanical behavior of commercially pure titanium

Nanostructure formation mechanism of α-titanium using SMAT

Ultrafine-grained (UFG) Ti samples have been prepared using equal channel angular pressing followed by cold rolling and annealing. The deformation behavior of these materials, including strain hardening, strain rate dependence of flow stress, deformation/failure mode, and tensile necking instability, have been systematically characterized. The findings are compared with those for conventional coarse-grained Ti and used to explain the limited tensile ductility observed so far for UFG or nanocrystalline metals.

Deformation behavior and plastic instabilities of ultrafine-grained titanium

Strain hardening of titanium: role of deformation twinning

Quasi-static and dynamic loading responses and constitutive modeling of titanium alloys

http://ceam.ucsd.edu/documents/papers/mechanicalproperties.pdf

Mechanical properties and deformation mechanisms of a commercially pure titanium

http://www-ceam.ucsd.edu/documents/papers/amodel.pdf

A model for experimentally-observed high-strain-rate dynamic strain aging in titanium

A unified constitutive model for strain-rate and temperature dependent behavior of molybdenum

The proportion of the coal and rock masses in different areas of surrounding rocks is quite different when a large-section coal roadway is excavated in gently inclined soft coal seams. Different creep failure occurs in coal and rock masses under high stress, which results in uneven deformations of roadways and difficulties in maintenance. This work studied the belt grooves of the 2103 working face in the lower coal group of the Wulihou Coal Mine. Theoretical analysis and measured geomechanical evaluation were used to analyze the failure causes of the surrounding rocks of the roadway. The failure law of large-section roadways in the gently inclined soft coal seams was studied using finite-difference numerical simulation software. Combined with the results of mathematical analysis, surrounding rocks were divided into regions. Surrounding-rock control schemes for different areas, such as grouting reinforcement, strengthening support, and pressure-relief grooving, were proposed separately and verified by numerical simulations. Strengthening the supports could reduce the deformations of area I, and pressure-relief grooving could control the deformations of area IV. The roadway and support system formed an anchored composite supporting body after grouting reinforcement, which greatly improved the bearing capacity and controlled the deformations of surrounding rocks. The fine on-site application effect and the improved non-symmetrical deformation verified the theoretical analysis, numerical simulations, and control technologies. The results provide a scientific basis and useful reference for similar projects.

/pdf/the-failure-law-and-control-technology-of-large-section-1cbxg2ps.pdf

The Failure Law and Control Technology of Large-Section Roadways in Gently Inclined Soft Coal Seams

Measuring the straightness of the scraper conveyor, which is an indispensable piece of equipment in a fully mechanized coal face, can prevent accidents such as derailment of the shearer and is also important for the precise positioning of the shearer and the accurate control of the hydraulic support. The existing scraper conveyor straightness measurement methods have the disadvantages of inconsistent measurement cost, accuracy, and reliability as well as low dimension of straightness description. To this end, this paper proposes a method for monitoring the three-dimensional straightness of a scraper conveyor based on binocular vision. Trapezoidal window matching technology was used to realize the image acquisition of multiple stations and multiple sensors. The bit pose acquisition model of binocular vision 3D reconstruction was used to obtain the 3D coordinates of the feature points on the sign board in each local coordinate system and the bit pose information of each sign board. The pose relay videometric method was used to convert the straightness in each local coordinate system to the global coordinate system to realize the 3D reconstruction of the scraper conveyor. Finally, the straightness measurement test of the preset scraper conveyor was carried out, and the error analysis was carried out by comparing with the manual measurement results, which showed that the measurement errors were all within ±30 mm. At the same time, the standard deviation of errors in both directions was small, which indicates that the straightness measurement method for the scraper conveyor in this paper has high reliability. In addition, the visual measurement process is independent of each other, so there is no error accumulation in the visual straightness measurement method. The analysis shows that the method of measuring the straightness of a scraper conveyor based on binocular vision can realize continuous and real-time monitoring of the scraper conveyor.

https://www.mdpi.com/2227-7390/10/19/3545/pdf?version=1665646680

Jingyi Cheng

Papers

Mechanical properties and deformation mechanisms of a commercially pure titanium

A model for experimentally-observed high-strain-rate dynamic strain aging in titanium

A unified constitutive model for strain-rate and temperature dependent behavior of molybdenum

The Failure Law and Control Technology of Large-Section Roadways in Gently Inclined Soft Coal Seams

Research on a Real-Time Monitoring Method for the Three-Dimensional Straightness of a Scraper Conveyor Based on Binocular Vision