NUMERICAL STUDY OF THE STRESS-STRAIN STATE OF THE PP-63 PNEUMATIC ROCK DRILL PISTON-STRIKER UNDER IMPACT LOADING

УДК 622.765:553.495

Abstract

Improving the reliability and energy transfer efficiency of pneumatic perforators is currently one of the most urgent and important problems in the mining industry. This scientific article investigates the complex dynamics of the impact process, as well as the stress-strain state during the interaction of the ПП-63 perforator striker, drill rod, and hard rock. Therefore, the primary objective of this research is to evaluate the stress concentration zones in the standard striker and scientifically justify the transition to a structurally optimized geometric profile capable of generating maximum energy pulses to enhance drilling productivity. The primary research work was performed using the method of numerical modeling in the modern ANSYS Explicit Dynamics software suite. During the work, the nature of the temporal and spatial distribution of the shock wave was deeply analyzed, and the phases of energy exchange were determined. The obtained results clearly showed that the maximum foci of equivalent elastic strain in the striker body are concentrated not on the impact surface itself, but in zones of abrupt change in geometric shape, namely in cylindrical stepped transitions. These dangerous zones strongly accumulate high-frequency cyclic stresses as a result of the interference of reflected waves, which over time can directly lead to fatigue failure of the detail. Conducted dynamic analyses scientifically and fully substantiate the need for targeted geometric optimization of the striker profile, namely the transition to a semi-catenoid shape, to reduce the amplitude of oscillations and ensure the smooth passage of the shock wave within the entire system.

Аннотация

Повышение надежности и эффективности передачи энергии пневматических перфораторов является сегодня одной из наиболее актуальных и важных задач горной промышленности. В данной научной статье детально исследуется сложная динамика ударного процесса, а также напряженно-деформированное состояние при взаимодействии поршня-ударника перфоратора ПП-63, буровой штанги и твердой горной породы. В связи с этим, основная цель данного исследования заключается в оценке зон концентрации напряжений в стандартном поршне-ударнике и научном обосновании перехода на конструктивно оптимизированный геометрический профиль, способный генерировать максимальные импульсы энергии для повышения производительности бурения. Основное исследование выполнено с использованием метода численного моделирования в современном программном комплексе ANSYS Explicit Dynamics. Был глубоко проанализирован характер временного и пространственного распределения ударной волны, определены фазы энергообмена. Полученные результаты наглядно показали, что максимальные очаги эквивалентной упругой деформации в теле ударника концентрируются не на самой ударной поверхности, а в зонах резкого изменения геометрической формы, то есть в цилиндрических ступенчатых переходах. Эти опасные зоны сильно аккумулируют высокочастотные циклические напряжения в результате интерференции отраженных волн, что со временем может напрямую привести к усталостному разрушению детали. Проведенные динамические анализы научно и полностью обосновывают необходимость целенаправленной геометрической оптимизации профиля ударника, а именно перехода на полукатеноидную форму, для снижения амплитуды колебаний и обеспечения исключительно плавного прохождения ударной волны внутри всей системы.

Keywords: Pneumatic perforator, Piston-striker, Shock wave, Equivalent elastic strain, Stress-strain state, Numerical modeling, ANSYS Explicit Dynamics, Geometric optimization,  Fatigue failure.

Ключевые слова: Пневматический перфоратор, Поршень-ударник, Ударная волна, Эквивалентная упругая деформация, Напряженно-деформированное состояние, Численное моделирование, ANSYS Explicit Dynamics, Геометрическая оптимизация.

Introduction

Currently, the use of modern computer technologies enables a deep and comprehensive investigation of impact processes. Compared to traditional experimental methods, numerical modeling and computational technologies offer high accuracy, time efficiency, and material resource savings, while also allowing for a detailed analysis of complex physical processes.

In the study of impact and high-velocity dynamic processes, software packages such as Abaqus (SIMULIA), SolidWorks Simulation, ANSYS LS-DYNA, and ANSYS Explicit Dynamics are widely applied. Based on specialized computational algorithms, these software tools ensure the simulation of complex dynamic processes occurring within extremely short time intervals and enable a comprehensive analysis of impact loads.

In this paper, the ANSYS Explicit Dynamics software package was utilized to analyze the impact processes. This software product is designed for modeling high-velocity impacts, collisions, and contact problems, providing calculations under conditions that closely replicate real physical processes. With its assistance, the following main results can be obtained:

• time-dependent stress and strain distribution during the impact process;
• the shape and amplitude of the impact pulse;
• energy transmission, absorption, and reflection processes;
• maximum and critical stresses arising within structural elements;
• the formation of elastic and plastic deformation zones in materials [3,4].

Using the ANSYS Explicit Dynamics software package, the interaction processes between the ПП-63 rock drill piston-striker, drill rod, bit, and rock, as well as the characteristics of energy exchange and the development of the stress-strain state, were investigated in detail. This software package serves as an efficient tool for the scientifically grounded analysis of impact systems, optimization of design parameters, and enhancement of the operating efficiency of piston-strikers.[1]

To perform numerical modeling of the pneumatic perforator impact system in the ANSYS Explicit Dynamics software suite, the following initial physical, mechanical, and structural parameters were defined:

Piston-Striker: The geometric dimensions were synchronized with the technical specifications of the commercial ПП -63 pneumatic perforator. The striker material was modeled with a density of ρ= 7800 kg/m³ Under the nominal operating regime of the perforator, the initial impact velocity of the striker hitting the drill rod was set to v= 8 m/s.

Drill Rod: The construction corresponds to the ШБШ-25 hexagonal drill steel with a total length L = 1000 mm, a shank size of 25 mm, and a 7⁰ tapered cone connection at the bit end. The rod is composed of U7 tool steel with a material density of ρ = 7830 kg/m³.

Drill Bit (Corona): Structural models utilized drilling bits made of advanced chromium-cobalt and silver-palladium alloys to represent realistic wear-resistant interfaces.

Rock Medium: Granite was selected as the target rock medium for the simulation. The justification for choosing granite is its predominance in the geological profiles of most underground mines and shafts in Uzbekistan. The physical and mechanical properties of the granite medium were defined as follows: density ρ= 2600 kg/m³, Mohs hardness scale value of 5, Protodyakonov rock strength coefficient f = 15, Young's modulus ranging between E =21 – 70 GPa, and Poisson's ratio varying from μ = 0,04 – 0,27 [11].

To address the gaps in previous studies, the main aim of this research is the numerical simulation and scientific justification of optimizing the geometric shape of a pneumatic perforator striker. In particular, this work uses ANSYS Explicit Dynamics to evaluate stress concentration zones and justifies adopting optimal pulse-generating shapes to improve both reliability and drilling efficiency.

Materials and methods

Within the framework of the study, the numerical modeling results obtained in ANSYS Explicit Dynamics allowed for determining the dynamics of strain variations during the contact interaction between the pneumatic rock drill piston-striker, the drill steel, and the rock (Fig. 1). The motion and deformation of the system elements were studied as a function of time (t=0…0,01 sec).

Initial impact and contact phase (t = 0…0,0025 sec): During the initial impact of the striker against the drill steel (at approximately 1,5·10-3 sec), the first peak of kinetic energy conversion into elastic strain energy is observed. At this moment, the rock deformation (green line) makes a sharp jump, reaching 1,04·10^-2 m. In the striker material (blue line), local strains of medium amplitude also arise due to inertial motion and the impact pulse. Notably, the drill steel (red line), acting as a transmitting element, undergoes virtually no longitudinal deformation (values are close to zero) owing to its high rigidity modulus. This confirms that the energy is transmitted directly to the rock with practically no losses due to the deformation of the tool itself [6,7].

Figure 1. Stress-strain state of the striker-drill steel-rock system during the impact process

System stabilization and rock fragmentation phase (t =0,003…0,01 sec): After the reflection of the primary shock wave (around t = 0,003), the rock deformation briefly decreases to a minimum value of 2,41∙10^-4 m. Following this short recovery phase, the system enters a stable operating regime, and the rock deformation begins to increase sharply according to a linear law. By 0.01sec, the total rock deformation reaches its maximum value of 5,021∙10^-2 m. This state indicates the full development of microcracks within the structure and the intensification of the actual rock mass fragmentation process. The striker also demonstrates a consistent growth dynamic along the sliding trajectory of the operating cycle [8,10].

In order to evaluate the fatigue strength of the system elements and identify zones with a high risk of failure, the spatial plots of equivalent elastic strain within the drill steel and the striker were analyzed (Fig. 2 and Table 1).

Figure 2. Time-dependent dynamics of equivalent elastic strain within the piston-striker

Table 1. Strain values in the striker–drill steel–rock system under impact loading obtained via ANSYS

Stress concentration zones in the piston-striker: The 3D strain pattern of the striker revealed a critical issue in impact mechanics. The highest point of equivalent elastic strain (1,97·10^-4m/m) is located not on the impact surface, but in the zone of a sharp change in the component's geometric shape — just below the transition zone between the enlarged head and the cylindrical body. The compression wave generated during the impact travels inside the striker, and upon its reflection, the mass differential creates a severe stress concentration precisely in this cylindrical section. The upper part of the striker, possessing a larger mass, undergoes virtually no deformation (Fig.3) [5,8].

To evaluate the complex dynamic nature of the impact process, the time-dependent variation of the equivalent elastic strain within the piston-striker was analyzed.

Figure 3. Elastic strains arising in the "striker–drill steel–rock" system during impact. The green line indicates the deformation of the drill steel (rod); the blue line represents the deformation occurring in the rock; the red line shows the deformation of the piston-striker

Peak amplitudes and wave interference: The plot demonstrates that the maximum strain within the striker is not limited to a single sharp impact, but over time forms specific resonance oscillations. The first major peak occurs at t=2·10^-3 sec reaching 3,94·10^-4 m/m. Following this, at t=3,5·10^-3 sec, the wave forms a second peak with practically the same amplitude (3,93·10^-4 m/m). These successive amplitudes are the result of the superposition (interference) of shock waves reflected from the impact and rear surfaces of the striker. [2,10]

Results and discussion

The analytical results obtained within the ANSYS Explicit Dynamics software suite demonstrated that the stress-strain state under impact loading is significantly higher in standard cylindrical piston-strikers. A common characteristic observed for this geometric profile is that the maximum strains are localized in the central section of the piston and within the zones adjacent to the contact interface along the direction of the impact (Figure 2). This phenomenon is inherently driven by the propagation of longitudinal elastic waves through the striker body and their mutual superposition during dynamic loading.

At the same time, the quantitative evaluation of the stress-strain fields (as shown in Table 1) indicates substantial negative changes in the profile. In the standard stepped piston-striker, high-frequency cyclic stresses accumulate abruptly at the cylindrical transitions, with the maximum equivalent strain reaching 1,97⋅10^-4 m/m. This high concentration is caused by the sudden change in the cross-sectional area, which impedes the free propagation of the shock wave.

Optimizing the geometric shape of the piston-striker–specifically by transitioning to stepped configurations–enables the successful mitigation of reflected wave interference and reduces the maximum equivalent stress. Compared to the standard model, a uniform strain distribution prevents the localization of high-frequency dynamic stresses in hazardous zones. This scientifically proves that the optimized stepped piston-striker shape significantly lowers the risk of fatigue failure and enhances the operational reliability of the ПП-63 perforator under high-stress mechanical impacts.

Conclusion

Comparative analyses demonstrated that optimizing the geometric profile, as opposed to conventional configurations, significantly alters the localized stress-strain state. The methodology validated in this study provides a robust, scientifically grounded CAD/CAE foundation for predicting structural fatigue, preventing sudden operational failures, ensuring mining industrial safety, and substantially extending the service life of high-stress impact mechanisms and rock-drilling machinery.

Given the high susceptibility of conventional cylindrical piston-strikers to severe deformation, it is imperative to develop a comprehensive design methodology for modifying the structural profile of pneumatic rock drill strikers. Future research must focus on engineering optimized geometric configurations capable of generating maximum force impulses while minimizing localized strain energy accumulation.

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