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Logs are valuable information for oil and gas fields as they help to determine the lithology of the formations surrounding the borehole and the location and reserves of subsurface oil and gas reservoirs. However, important logs are often missing in horizontal or old wells, which poses a challenge in field applications. To address this issue, conventional methods involve supplementing the missing logs by either combining geological experience and referring data from nearby boreholes or reconstructing them directly using the remaining logs in the same borehole. Nevertheless, there is currently no quantitative evaluation for the quality and rationality of the constructed log. In this paper, we utilize data from the 2020 machine learning competition of the Society of Petrophysicists and Logging Analysts (SPWLA), which aims to predict the missing compressional wave slowness (DTC) and shear wave slowness (DTS) logs using other logs in the same borehole. We employ the natural gradient boosting (NGBoost) algorithm to construct an Ensemble Learning model that can predicate the results as well as their uncertainty. Furthermore, we combine the SHAP (SHapley Additive exPlanations) method to investigate the interpretability of the machine learning model. We compare the performance of the NGBosst model with four other commonly used Ensemble Learning methods, including Random Forest, GBDT, XGBoost, LightGBM. The results show that the NGBoost model performs well in the testing set and can provide a probability distribution for the prediction results. This distribution allows petrophysicists to quantitatively analyze the confidence interval of the constructed log. In addition, the variance of the probability distribution of the predicted log can be used to justify the quality of the constructed log. Using the SHAP explainable machine learning model, we calculate the importance of each input log to the predicted results as well as the coupling relationship among input logs. Our findings reveal that the NGBoost model tends to provide greater slowness prediction results when the neutron porosity (CNC) and gamma ray (GR) are large, which is consistent with the cognition of petrophysical models. Furthermore, the machine learning model can capture the influence of the changing borehole caliper on slowness, where the influence of borehole caliper on slowness is complex and not easy to establish a direct relationship. These findings are in line with the physical principle of borehole acoustics. Finally, by using the explainable machine learning model, we observe that although we did not correct the effect of borehole caliper on the neutron porosity log through preprocessing, the machine learning model assigned a greater importance to the influence of the caliper, achieving the same effect as caliper correction.

The analysis of the main factors of brittleness is an important basis for the selection of engineering desserts in shale oil reservoirs. In this study, with the shale oil reservoir of the Liushagang Formation in the X Depression of the Beibuwan Basin as the research object, a characterization and analysis of the main factors of brittleness of the reservoir was performed in order to further reveal the brittleness of shale reservoirs in the study area. The brittleness of reservoirs in the study area was controlled by both internal and external factors, and the main factors of brittleness in the target section included the maturity of organic matter, horizontal stress difference, and brittle minerals. As the maturity of organic matter increased, the density, elastic modulus, and hardness of casein increased and the differentially hardened internal structure occurred and significantly affected brittleness. The mineral composition of the reservoir was characterized by complex mineral types and high contents of brittle minerals, and the minerals determining brittleness were mainly quartz, feldspar, calcite, and dolomite. The horizontal stress difference of the shale oil section was relatively small and contributed to fracturing and reforming. This study clarified the brittleness characteristics of E2l shale and its main factors, and provided a basis for the selection of shale formation geo-engineering dessert layers in the study area.

A systematic study of the pore structure characteristics of Lower Cambrian shales in the southeastern Upper Yangtze Platform, was conducted using organic geochemistry, mineralogy, nitrogen adsorption, physical property analysis, and scanning electron microscopy. The results indicate that: 1) The Total organic carbon (TOC) content shows a strong correlation with quartz and clay minerals. Shales with low TOC content and rich in clay minerals primarily exhibit slit-shaped and narrow slit-like inter-clay particle pores with pore size distribution is dominated by mesopores and macropores. Shales with high TOC content predominantly feature narrow slit-like and ink bottle-shaped pores with pore size distribution dominated by micropores and mesopores. 2) Shale pore structures vary significantly under different gas content and preservation conditions. Shales under favorable preservation conditions exhibit a relatively “high porosity, low permeability, and high gas content” pattern, with well-developed organic pores and a strong pore-permeability correlation. In contrast, shales under unfavorable preservation conditions appear dense, with excessively developed fractures increasing both average pore size and local permeability. The pore-permeability correlation is weak, presenting a relatively “low porosity, high permeability, and low gas content” pattern. 3) TOC content plays a crucial role in controlling pore structure, showing overall positive correlations with pore volume, specific surface area, and porosity, and negative correlations with pore size. High TOC content enhances shale plasticity, resulting in lower pore diameters. Factors such as compaction and unfavorable preservation conditions lead to the shrinkage, collapse, and closure of some narrow pore throats, negatively impacting pore volume, specific surface area, brittleness, and fractal dimension, exhibiting a negative correlation with TOC content. 4) The pore structure of Lower Cambrian shales is complex, with fractal dimensions D1 and D2 exhibiting negative correlations with average pore size and positive correlations with TOC, specific surface area, and total pore volume. A high D1 value indicates well-preserved nanoscale pore surface structures with low complexity, suggesting minimal alteration by external fluids and better shale gas preservation. D1 serves as an indicator for shale gas content and preservation conditions. D2 shows better correlations with various pore structure parameters, making it suitable for characterizing pore structures.

Passive vibration isolation techniques with low-frequency characteristics have been a hot topic in the aerospace field. A hydraulic inertial vibration isolator is a highly effective type of isolator for controlling low-frequency vibrations. It typically consists of a main spring, a minor spring, an inertial mass, and a fluid domain. Due to its multi-domain nature, analyzing the isolation mechanism of this type of isolator is challenging. The bond graph method is employed to establish the dynamic model of the isolator. Subsequently, the state equations of the isolator are derived, and the energy equations of both the mechanical and the fluid parts of the isolator are obtained. Based on this, the energy transfer characteristics between the mechanical and fluid domains inside the isolator under external excitation are discussed. The time-domain response of the forces transmitted to the foundation is analyzed. It is shown that the anti-resonance frequency occurs when the forces transmitted to the foundation generated by the main spring and the fluid pressure are equal to that of the minor spring. To verify the proposed method’s correctness, a prototype of the isolator is designed and a carefully designed experiment is conducted. The acceleration transmissibility of the isolator is used to conduct a comparative study. The results show that the theoretical results are in good agreement with the experimental results. To depict the dynamic characteristics of the isolator under large amplitude vibration, the nonlinear dynamic model of the isolator is developed, and the corresponding force transmissibility of the isolator is formulated. The energy flow between the mechanical and the fluid domains under this condition is also analyzed. The results indicate that the energy flow responses exhibit a similar change tendency to the force transmissibility. However, the peak of the energy ratio between the mechanical subsystem and the fluid is the same as the linear condition, suggesting that this value is determined by the amplification ratio of the isolator. This research provides enhanced physical insight to understand the dynamic characteristics of this type of isolator and will help to shorten the design cycle of the isolator.

The exploration and comprehensive assessment of fractured-vuggy reservoir information have perennially constituted focal points and challenges within the domain of oil and gas reservoir evaluation. The verification of geological phenomena, identification of various fracture and hole types, and the quantitative characterization thereof currently present pressing challenges. This study meticulously examines the deep carbonate reservoirs within the Dengying Formation in the Penglai gas region of the Sichuan Basin. The Core Rolling Scan images reveal five discernible features: unfilled holes, filled holes, filled fractures, open fractures, and algae. The analysis pinpoints three primary challenges in semantic segmentation recognition: the amalgamation of feature scales, class imbalance, and the scarcity of datasets with substantial sample sizes. To address these challenges, this paper introduces a Multi-Scale Feature Aggregation Pyramid Network model (MFAPNet), achieving a pixel accuracy of 68.04% in recognizing the aforementioned five types. Lastly, the model is employed in calculating core porosity, exposing a scaling relationship between wellbore image porosity and core porosity ranging from 1.5 to 3 times. To a certain extent, it reveals the correlation between the wellbore image logging data and the actual formation of the Dengying Formation in the Penglai Gas Field of the Sichuan Basin, and also provides a basis for the subsequent logging evaluation of the formation. The partial code and CHA355 dataset are publicly available at https://github.com/zyng886/MFAPNet.

AbstractThe reservoir property of tight sandstones is closely related to the provenance and diagenesis, and multiprovenance system and complex diagenesis are developed in Hangjinqi area. However, the relationship between provenance, diagenesis, and physical characteristics of tight reservoirs in Hangjinqi area has not yet been reported. The Middle Permian Lower Shihezi Formation is one of the most important tight gas sandstone reservoirs in the Hangjinqi area of Ordos Basin. This research compared the diagenesis-porosity quantitative evolution mechanisms of Lower Shihezi Formation sandstones from various provenances in the Hangjinqi area using thin-section descriptions, cathodoluminescence imaging, X-ray diffraction (XRD), scanning electron microscopy (SEM), and homogenization temperature of fluid inclusions, along with general physical data and high-pressure mercury intrusion (HPMI) data. The sandstones mainly comprise quartzarenite, sublitharenite, and litharenite with low porosity and low permeability and display obvious zonation in the content of detrital components as a result of multiprovenance. Pore space of those sandstone mainly consists of primary pores, secondary pores, and microfractures, but their proportion varies in different provenances. According to HPMI, the order of the pore-throat radius from largest to smallest is central provenance, eastern provenance, and western provenance, which is consistent with the change tend of porosity (middle part>northern part>western part) in Hangjinqi region. The diagenetic evolution path of those sandstones is comparable, with compaction, cementation, dissolution, and fracture development. The central provenance has the best reservoir quality, followed by the eastern provenance and the western provenance, and this variation due to the diverse diagenesis (diagenetic stage and intensity) of different provenances. These findings reveal that the variations in detrital composition and structure caused by different provenances are the material basis of reservoir differentiation, and the main rationale for reservoir differentiation is varying degrees of diagenesis during burial process.

Brittleness is important in the evaluation of the fracturing ability of shale reservoir and has a significant impact on shale gas exploration and development. This paper discusses the characteristics and controlling factors of brittleness of continental shale in the Da’anzhai Member of the Ziliujing Formation of Lower Jurassic age in the northeast Sichuan Basin. Continental shale lithofacies and their associations were grouped into four main rock types: clayey shale, silty shale, shell calcareous clayey shale, and silty clayey shale, characterized by the high clay content and local enrichment of carbonate minerals as a whole. Compared with the marine shale, the continental shale contained a low content of siliceous minerals, a high content of carbonate minerals, and a large number of shell limestone interlayers. Carbonate minerals play an important role in controlling the brittleness of continental shale. The shale interlayers were mainly shell limestone interlayers with a thickness of several centimeters and a large number of shell laminates with thicknesses of several millimeters were also observed. The shell laminates were mainly filled with calcite. Due to the dissolution process, a large number of bedding joints and corrosion joints were formed in the calcite shell layers. In the interlayers with a high shell content, a large number of microfractures developed. The energy consumption required for maintaining fracture expansion was lower after fracturing; the fractures greatly improved the reservoir’s brittleness.

The marine shale of southern China is characterized by old sedimentary formations, multiple tectonic activities, and poor preservation conditions. The fracture system in this shale reservoir is extraordinarily complex, greatly adding to difficulties for shale gas exploration and development. Based on field surveys, drilling cores, seismic data interpretation, and experimental tests, we try to characterize the developmental characteristics of shale fractures at different scales and delineate the stages of fractures in the Cen’gong block. The results show that the Cen’gong block is a saddle-shaped structure formed by the northeast-oriented Banxi anticline and the southwest-oriented Lannigan anticline. There are four types of core fractures developed in the study area, namely, pyrite-filled fractures, fibrous veins, subvertical fractures, and slip fractures, and the forming time of these fractures are later in turn based on the intersecting relationships and analysis of filling minerals. The fracture rose diagram and the paleomagnetic orientation experiments indicate that the fracture direction is mainly NNE and partly NW, consistent with the direction of faults identified in the seismic data. Quantitative statistics have been conducted for fracture aperture, length, and density distribution. The fracture abundance has a close relationship with buried depth and regional faults in the study area.

Tight sandstone reservoirs are affected by various factors such as pore structure, formation water salinity, and siliceous cementation, which lead to the abnormal phenomenon of high-resistivity water layers and increase the difficulty in identifying gas and water layers by conventional logging. In this study, the pore types and pore size distribution characteristics of tight sandstone reservoirs were firstly determined by NMR and high-pressure mercury injection experiments, and then the iterative least-square method was used to automatically optimize the inversion method of pseudo-capillary pressure curve and search for the optimal conversion coefficient. Finally, the apparent free water porosity was inversed and the fluid identification standard was obtained and applied. The results showed that the reservoirs mainly developed intergranular pores, cutting solution pores, and intergranular pores. The pore throats were poorly sorted, and the displacement pressure was high. The median radius ranged from 0.01 to 0.48 μm, and the main peak range was from 0.02 to 0.06 μm. Pores were of mainly small-hole fine throat type. In the inversion results of the optimal conversion coefficient, the correlation coefficient between the aperture parameters and the results of high-pressure mercury injection experiments was greater than 0.93. According to the fluid property identification standard based on nuclear magnetic apparent free water porosity, the high-resistivity water layers were effectively identified and its coincidence rate with the final field test was 10.7% higher than that of the conventional method. This identification method can be used to identify complex fluids in tight sandstone reservoirs.

In this study, the creep properties of cylindrical metal rubber (MR) specimen under static compression at elevated temperatures were investigated by a series of creep experiments. The cylindrical MR specimen has a good symmetrical property, and the mechanical properties are consistent in its different axial section. The failure determination parameters of MR under the coupling of thermal and mechanical static load of the forming direction were proposed in four aspects: the overall height, the average stiffness, the energy dissipation, and the variation of the loss factor. The variation patterns of the properties of the MR specimens were investigated with a static load at different temperatures for 324 h. The analytical equipment, including the simultaneous thermal analyzer (TGA/DSC), X-ray diffractometer (XRD), and scanning electron microscope (SEM), were used for material characterization and failure analysis. Based on the results, it is found that there are significant differences in the MR property variations subjected to creep tests at different elevated temperatures. The results indicated that an appropriate heat treatment for MR specimens would improve the creep resistance at elevated temperatures. In addition, the overall height and energy dissipation of the MR specimens were increased, and the average stiffness and the loss factor were decreased under the creep tests at 200 °C and 250 °C. However, under the creep tests at 25 °C, 300 °C, 350 °C, and 400 °C, the overall height, the energy dissipation and the loss factor were decreased, but the average stiffness was increased.

The purpose of this paper is to investigate the fatigue properties of C17200 alloy under the condition of quenching aging heat treatment at high temperatures, and to provide a design reference for its application in a certain temperature range. For this purpose, the tensile and rotary bending fatigue (RBF) tests were carried out at different temperatures (25 °C, 150 °C, 350 °C, and 450 °C). The tensile strength was obtained, and relationships between the applied bending stress levels and the number of fatigue fracture cycles were fitted to the stress-life (S-N) curves, and the related equations were determined. The fractured surfaces were observed and analyzed by a scanning electron microscopy (SEM). The results show that the RBF fatigue performance of C17200 alloy specimens is decreased with the increase in test temperature. When the temperature is below 350 °C, the performance degradation amplitudes of mechanical properties and RBF fatigue resistance are at a low level. However, compared to the RBF fatigue strength of 1 × 107 cycles at 25 °C, it is decreased by 38.4% when the temperature reaches 450 °C. It is found that the fatigue failure type of C17200 alloy belongs to surface defect initiation. Below 350 °C, the surface roughness of the fatigue fracture is higher, which is similar to the brittle fracture, so the boundary of the fracture regions is not obvious. At 450 °C, due to the further increase in temperature, oxidation occurs on the fracture surface, and the boundary of typical fatigue zone is obvious.

In this paper, the responses of machined surface roughness and milling tool cutting forces under the different milling processing parameters (cutting speed v, feed rate f, and axial cutting depth ap) are experimentally investigated to meet the increasing requirements for the mechanical machining of T2 pure copper. The effects of different milling processing parameters on cutting force and tool displacement acceleration are studied based on orthogonal and single-factor milling experiments. The three-dimensional morphologies of the workpieces are observed, and a white-light topography instrument measures the surface roughness. The results show that the degree of influence on Sa (surface arithmetic mean deviation) and Sq (surface root mean square deviation) from high to low level is the v, the f, and the ap. When v = 600 m/min, ap = 0.5 mm, f = 0.1 mm/r, Sa and Sq are 1.80 μm and 2.25 μm, respectively. The cutting forces in the three directions negatively correlate with increased cutting speed; when v = 600 m/min, Fx reaches its lowest value. In contrast, an increase in the feed rate and the axial cutting depth significantly increases Fx. The tool displacement acceleration amplitudes demonstrate a positive relationship. Variation of the tool displacement acceleration states leads to the different microstructure of the machined surfaces. Therefore, selecting the appropriate milling processing parameters has a positive effect on reducing the tool displacement acceleration, improving the machined surface quality of T2 pure copper, and extending the tool’s life. The optimal milling processing parameters in this paper are the v = 600 m/min, ap = 0.5 mm, and f = 0.1 mm/r.

The wave propagation and vibration transmission in metamaterial-based elastic rods with periodically attached multi-degree-of-freedom (MDOF) dynamic anti-resonant vibration isolator (DAVI) resonators are investigated. A methodology based on a combination of the transfer matrix (TM) method and the Bloch theorem is developed, yielding an explicit formulation for the complex band structure calculation. The bandgap behavior of the periodic structure arrayed with single-degree-of-freedom (SDOF) DAVI resonators and two-degree-of-freedom (2DOF) DAVI resonators are investigated, respectively. A comparative study indicates that the structure consisting of SDOF DAVI resonators periodically jointed on the metamaterial-based elastic rod can obtain an initial locally resonant band gap 500 Hz smaller than the one given in the published literature. The periodic structure containing 2DOF DAVI resonators has an advantage over the periodic structure with SDOF DAVI resonators in achieving two resonance band gaps. By analyzing the equivalent dynamic mass of a DAVI resonator, the underlying mechanism of achieving a lower initial locally resonant band gap by this periodic structure is revealed. The parameters of the 2DOF DAVI resonator are optimized to obtain the lowest band gap of the periodic structure. The numerical results show that, with the optimal 2DOF DAVI parameters, the periodic structure can generate a much lower initial locally resonant band gap compared with the case before the optimization.

The shale oil reservoir of the Lucaogou Formation in the Jimsar Sag has undergone tectonic movement, regional deposition and complex diagenesis processes. Therefore, various reservoir space types and complex combination patterns of pores have developed, resulting in an intricate pore throat structure. The complex pore throat structure brings great challenges to the classification and evaluation of reservoirs and the efficient development of shale oil. The methods of scanning electron microscopy, high-pressure mercury injection, low-temperature adsorption experiments and thin-slice analysis were used in this study. Mineral, petrology, pore throat structure and evolution process characteristics of the shale oil reservoir were analyzed and discussed qualitatively and quantitatively. Based on these studies, the evolution characteristics and formation mechanisms of different pore throat structures were revealed, and four progressions were made. The reservoir space of the Lucaogou Formation is mainly composed of residual intergranular pores, dissolved pores, intercrystalline pores and fractures. Four types of pore throat structures in the shale oil reservoir of the Lucaogou Formation were quantitatively characterized. Furthermore, the primary pore throat structure was controlled by a sedimentary environment. The pores and throats were reduced and blocked by compaction and cementation, which deteriorates the physical properties of the reservoirs. However, the dissolution of early carbonate, feldspar and tuffaceous minerals and a small amount of carbonate cements by organic acids are the key factors to improve the pore throat structure of the reservoirs. The genetic evolution model of pore throat structures in the shale oil reservoir of the Lucaogou Formation are divided into two types. The large-pore medium-fine throat and medium-pore medium-throat reservoirs are mainly located in the delta front-shallow lake facies and are characterized by the diagenetic assemblage types of weak compaction–weak carbonate cementation–strong dissolution, early medium compaction–medium calcite and dolomite cementation–weak dissolution. The medium-pore fine throats and fine-pore fine throats are mainly developed in shallow lakes and semi-deep lakes. They are characterized by the diagenetic assemblage type of strong compaction–strong calcite cementation–weak dissolution diagenesis. This study provides a comprehensive understanding of the pore throat structure and the genetic mechanism of a complex shale oil reservoir and benefits the exploration and development of shale oil.

Increasing load requirements and harsh operating conditions have worsened the wear of drive shafts in special field vehicles. In this paper, the evolution of the microstructure and fretting wear behaviors of 25CrNi2MoVE torsion shaft steel and their influence on the wear mechanisms were investigated as a function of tempering temperature. The results showed that the coarse grain size, low matrix hardness and non-metallic inclusions in the as-received state lead to a high wear rate and serious adhesive wear. The grain refinement after normalizing and the formed M5C2 carbide and bainite helped to improve the wear resistance and worn surface quality. Low temperature tempering is conducive to further improve the wear resistance of normalized samples, and the wear rate and worn surface roughness are increased gradually after tempering temperature increases. For quenching, although martensite structure can achieve a lower wear rate, the coefficient of friction is much higher; the wear mechanisms are primarily fatigue wear and adhesive wear. Although the adhesive wear degree and worn surface roughness were increased, the optimal anti-wear performances are obtained under tempering at 350 °C with good continuity of the surface oxide film. Excessive tempering temperature will make the softened matrix unable to form a beneficial “third-body wear”.

In this paper, the fretting wear properties of 20CrMnTi steel, a common material for a rocker bracket, was discussed for the first time after it was suffered carburizing treatment. Subsequently, the fretting wear behaviors of virgin, quenched, and carburized states were studied. The effect of loads (corresponding to different engine power output) and reciprocating frequencies (corresponding to different engine speed) on wear behaviors and mechanisms of carburized specimen were further discussed. The results showed that the coefficient of friction (CoF) and wear volume loss (WVL) of the carburized specimens were significantly lower than that of virgin and quenched states. During the wear test, the surface CoF decreased gradually with the increase of applied load, while the linear correlation trend was not observed with the increase of fretting frequency as it showed an increase first and then a decrease. It was observed that the WVL increased gradually with the increase of load and frequency. With an increase of the load, the wear mechanism gradually deteriorated from the initial adhesive wear to the mixed wear mechanism. When the load was high, the oxidative wear became more severe. However, no significant effect of frequency was observed on the wear mechanism.

Due to their design, hollow cavity and filled sodium, hollow head and sodium filled engine valves (HHSVs) have superior performance to traditional solid valves in terms of mass and temperature reduction. This paper presents a new manufacturing method for 42Cr9Si2 steel hollow head and sodium filled valves. An inertia friction welding process parameter optimization was conducted to obtain a suitable process parameter range. The fatigue strength of 42Cr9Si2 steel at elevated temperatures was evaluated by rotating bending fatigue test with material specimens. Performance evaluation tests for real valve components were then carried out using a bespoke bench-top apparatus, as well as a stress evaluation utilizing a finite element method. It was proved that the optimized friction welding parameters of HHSV can achieve good welding quality and performance, and the HHSV specimen successfully survived defined durability tests proving the viability of this new method. The wear resistance of the HHSV specimens was evaluated and the corresponding wear mechanisms were found to be those classically defined in automotive valve wear.

17Cr2Ni2MoVNb steel is a new type of gear steel in the automotive industry; the rolling contact fatigue behavior is not well documented. In this study, some microscopic analysis methods (optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), and energy dispersive X-ray analysis (EDS)) were used to characterize material microstructure and damage surface. In addition, rolling contact fatigue behavior was evaluated by Weibull curve. The results show that the size of austenite grain increased while the quenching temperature increased. Moreover, the samples with a quenching temperature of 1000 °C exhibited the maximum mean life of 7.33 × 105 cycles. In addition, the failure mode of quenched at 900 °C and 1100 °C were delamination, and pitting was the main failure mode of 1000 °C.

High-performance lightweight composites are developed by integrating metal rubber (MR) into a zinc alloy (ZA8) matrix via squeeze casting. MR, comprising 304 stainless steel wires (SSWs) with diameters of 0.15 mm, forms 3D network skeletons with volume fractions of 8.8 vol% (S1), 11.1 vol% (S2), and 13.4 vol% (S3), respectively. The preparation parameters of the composites are optimized, and their microhardness is investigated. Special attention is paid to the ultimate compression and shear performance at 25, 150, and 250 °C. The microstructure and failure analysis are performed via scanning electron microscopy. The results reveal a 48.0% increase in microhardness at composite interfaces relative to ZA8. At 25 °C, S2 possesses an ultimate compressive strength (UCS) of 401.4 MPa, which is 33.7% higher than that of ZA8. At 150 and 250 °C, S3 exhibits UCS values of 180.3 and 74.3 MPa, exceeding those of ZA8 by 61.7% and 110.5%, respectively. Meanwhile, the ultimate shear strength of composites slightly drops below that of the matrix: the corresponding value of S1 specimen (158.4 MPa) at 250 °C is 11.5% below that of ZA8. Therefore, compression and shear failure mechanisms of MR/ZA8 composites are quite intricate, involving SSW separation, necking, and ZA8 fractures. [ABSTRACT FROM AUTHOR]